Qatar Highway Design Manual.pdf

;ir.1 ,11 ~.aLJI· ;Ai" . I :i~Luu doJ,f.JJ'" .. . ~H Jo:!J'Introduction by H.E. Minister for Municipal Affairs and Agriculture

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The State of Qatar is witnessing rapiddevelopment and the road constructionsector is most closely connected with thisdevelopment. It is highly important whendesigning roads to take into considerationthe latest international standards andspecifications which in turn conform toenvironmental requirements and the futureneed to link the road network with thedevelopment programme.

Therefore, the initiative of the CivilEngineering Department in the Ministry ofMunicipal Affairs and Agricultural to update the Qatar Highway Design Manual,which was published for the first time in1989, is the best evidence of its desire tokeep up with the progress that this countryis witnessing and emphasises thedetermination of this Ministry that itsachievements are proof of its work.

We ask God to guide our steps to therighteous path.

.J.:!J~I '.!*ut.,)-t~ALI BIN SAEED AL KHAYAREEN

;ir.IJjll, ~.a4l1 ~h;.HJ1 Jo:!j,MINISTER OF MUNICIPAL AFFAIRS AND AGRICULTURE

• :UJljJl9~~1 ~9;,;:;t1 dJ1j9~9/d~""d.obIntroduction by H.E. the Undersecretary of the Ministry of Municipal Affairs

and Agriculture

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The Road Network represents the arteriesfor traffic movement in the modern state.Street~ are not just for pedestrian andtraffic movement but contain electricityand telephone cables, and seweragenetworks.

Therefore, the information that should beavailable for the road designer should notbe confined to population density, thenature of land and its topography only.The designer has to coordinate withservice authorities and study thedevelopment progress of the area, itsenvironment and the effects of roadconstruction and the movement of traffic.

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The publication of the Qatar HighwayDesign Manual, in a new issue by the CivilEngineering Department, is undoubtedly astep in the right path, and is the fastestway to reach our objective.

God is behind our purpose and will guide . ~I <?~ JAJ ,,,'1\ ~I.JJ (}o '&IJus on the right path.

-p'JI¢d1 ~.,).f~ALI BIN 5AAD AL KUWARI

:UIJjJI9~~1 ~9;4il1 dJ1j9~9UNDERSECRETARY OF THE MINISTRY OF MUNICIPAL AFFAIRS

AND AGRICULTURE

• ;L.J~I ;Lu.Li.dJ1 d l.il 1.u.auJ1~.. J ..h!'*o ..Introduction by the Director of Civil Engineering Department

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This is the second issue of the QatarHighway Design Manual we present toengineers working in the roads andconstruction sector in the State of Qatar.

The first issue was published in December1989 and we have been eager that thisissue should contain more details of themethods and ideas which have developedduring this period regarding the design andconstruction of roads, especially thoseadopted in the USA, UK and othercountries in the last few years.

Whilst it is the intention of this Manual tobe used in the road construction sector,never the less, it should not be consideredthe only source; it is only a guide tohighway engineers. The engineer needs toresearch, review and be assisted by otherscientific sources. The Manual does notcover the area of traffic engineering andrelated matters such as planning andtransportation studies and issues of generalpolicy, We will welcome any observations,suggestion or additions for future issues.

The Civil Engineering Department whileworking earnestly to benefit from newengineering developments to keep up withthe times, requests all those specialising inroad design in the State of Qatar toimplement the specifications and standardscontained in this Manual.

May god gives us the fortune to carry outthe trust we bear and to do what benefitsthe Country.

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~I.:iJl jo13U .:H~ALI BIN NASSER AL THANI

d.! i.i.oll ;Lu.i..i..dJ1 djl.i!~.ioDIRECTOR OF CIVIL EN<5INEER.IN<5 DEPARTMENT

•QATAR HIGHWAY DESIGN MANUAL

DOCUMENT HISTORY

DOCUMENT HISTORY

The purpose of the Document History is to record changes to the Qatar Highway Design Manual. In theevent of a revision to the manual, CEO will issue the amended pages and re-issue the DocumentHistory.The Document History pages should contain a description of the change, the issue reference and thedate of issue as noted below. The updated Document History should replace the superseded historyand the revised pages of the manuai should be placed in the appropriate position in the manual.

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Description

Qatar Highway Design Manual

Qatar Highway Design Manual

January 1997

Issue

Original Issue

2nd Edition (Rev 0)

Date

December 1989

January 1997

Page DH/1

QATAR HIGHWAY DESIGN MANUAL ACKNOWLEDGEMENTS

• The Qatar Highway Design Manual draws on technical input and experience from a number ofrecognised international sources and applies these to the road system requirements for Qatar. Withinthe text there are references to publications where the engineer may seek further information on aspecific topic. The main reference sources are acknowledged below:

• Qatar Construction Specification• Qatar Traffic Manual• Design Manual for Road and Bridgeworks· British Government Highway Agency• Policy on Geometric Design of Highways . American Association of State Highway and

Transportation Officials.• Road Design Manual· National Association of Australian State Road Authorities.• Designing for Deliveries· Freight Transport Association .

•

Section 6 Copyright Acknowledgement

Section 6 of this manual contains text and diagrams which are based on material contained within the British Government'sHighways Agency publication the "Design Manual for Road and Bridges - Volume 6 Section 2.

Crown copyright material has been adapted with the permission of the controller of Her Majesty's Stationery Office and theHighways Agency who do not accept any responsibility for the accuracy or comprehensiveness of the contents this Manual.

January 1997 Page AK/1

QATAR HIGHWAY DESIGN MANUAL

CONTENTS

CONTENTS

Page No.

GLOSSARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G/1

ROAD SYSTEM IN QATAR.............................................. RSQ/1The Highway NetworkPrimary RoutesSecondary RoutesTertiary RoutesThe Route ClassificationQatar Area Zones

,.SECTION 1Clause 1.1Clause 1.2Clause 1.3Clause 1.4Clause 1.5Clause 1.6Clause 1.7Clause 1.8Clause 1.9

SECTION 2Clause 2.1Clause 2.2Clause 2.3Clause 2.4Clause 2.5Clause 2.6

DESIGN SPEEDGeneral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/1Design Speed Related Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . 1/1Selection of Design Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Posted Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Changeover of Design Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Changeover to Existing Roads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Selection of Parameter Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Relaxations and Departures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/2Special Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1/3

SIGHT DISTANCEGeneral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2/1Stopping Sight Distance. . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . 2/1Full Overtaking Sight Distance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2/1Obstructions to Sight Distance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2/2Effect of Horizontal Curves on Sight Distance. . . . . . . . . . . . . . . . 2/2Special Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2/2

SECTION 3Clause 3.1Clause 3.2Clause 3.3Clause 3.4Clause 3.5Clause 3.6Clause 3.7Clause 3.8

SECTION 4Clause 4.1Clause 4.2Clause 4.3Clause 4.4Clause 4.5Clause 4.6Clause 4.7

SECTION 5Clause 5.1Clause 5.2Clause 5.3Clause 5.4Clause 5.5Clause 5.6

January 1997

HORIZONTAL ALIGNMENT .General .Minimum Curvature .Transition Curves .Camber and Superelevation .Widening on Curves .Harmonising the Alignment .Horizontal Clearances .Special Considerations .

VERTICAL ALIGNMENTGeneral Controls .Maximum and Minimum Grades .Vertical Curves .Harmonising the Vertical Alignment .Phasing Horizontal and Vertical Alignment .Vertical Clearances .Special Considerations .

CROSS SECTIONAL ELEMENTSRoad Reservations .Lane Widths .Lane Capacity .Shoulders , .Edge Strips and Shy Distances .Medians .

3/13/13/13/23/63/83/103/12

4/14/14/24/34/54/94/10

5/15/115/125/125/135/13

Page C/1

QATAR HIGHWAY DESIGN MANUAL . CONTENTS

Clause 5.7Clause 5.8Clause 5.9Clause 5.10Clause 5.11Clause 5.12Clause 5.13Clause 5.14Clause 5.15Clause 5.16Clause 5.17Clause 5.18Clause 5.19

Verges .Parking Bays and Lanes .Side Slopes .Auxiliary Lanes .Service Roads .Pedestrian Facilities .Utilities .

. Use of Kerbs .Safety Fences .Crash Cushions .Fencing .Road Closure .Landscaping .

5/145/155/165/175/175/185/195/195/205/265/275/275/30

SECTION 6Clause 6.1

Clause 6.2

Clause 6.3

Clause 6.4Clause 6.5Clause 6.6

Clause 6.7

January 1997

JUNCTIONSGeneral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/16.1.1 Junction Spacing6.1 .2 Traffic Flows6.1.3 Design Vehicles6.1.4 Siting of JunctionsTypes of Junction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . 6/66.2.1 T-Junction6.2.2 Simple Crossroads6.2.3 Staggered Junction6.2.4 Skew or Y·Junction6.2.5 Roundabout6.2.6 Grade Separated Interchange6.2.7 Traffic SignalsJunction Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/76.3.1 Status of Intersecting Roads6.3.2 Continuity of Standard6.3.3 Junction CapacityMajor/Minor Junctions - General. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/9Safety At Major/Minor Junctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/9Major/Minor Junction Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/96.6.1 The Simple T-Junction6.6.2 T-Junction with Ghost Island6.6.3 T-Junction with Single Lane Dualling6.6.4 T-Junction on a Dual Carriageway with Median

Opening (Signalized)6.6.5 T-Junction on a Dual Carriageway with Carriageway

Separation6.6.6 Crossroads6.6.7 Staggered Junction6.6.8 Right and Left Hand Skew JunctionMajor/Minor Junction Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/146.7.1 General6.7.2 Design Speed6.7.3 Visibility6.7.4 Corner Radii6.7.5 Carriageway Widths6.7.6 Central Islands - Major Road6.7.7 Central Island Tapers6.7.8 Turning Length in Median6.7.9 Direct Taper Length6.7.10 Left Turning Lanes6.7.11 Median Openings6.7.12 Traffic Islands6.7.13 Nearside Diverging Tapers and Auxiliary Lanes6.7.14 Merging Tapers

Page C/2

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Clause 6.8

Clause 6.9

Clause 6.10

Clause 6.11Clause 6.12Clause 6.13

Clause 6.14Clause 6.15

Clause 6.16

January 1997

CONTENTS

6.7.15 Stagger Distances6.7.16 Skew Junctions6.7.17 T-Junction with Carriageway Separation6.7.18 Channelizing Islands6.7.19 Splitter/Right Turn Islands6.7.20 Drainage and Crossfall6.7.21 Traffic Signs and Road Markings6.7.22 Road LightingRoundabouts· General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/336.8.1 General Principles6.8.2 Types of RoundaboutSafety at Roundabouts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/356.9.1 General6.9.2 Two Wheeled Vehicles6.9.3 Large Goods VehiclesRoundabout Elements ..: , " 6/386.10.1 Definitions6.10.2 Entries6.10.3 Entry Width6.10.4 Flare Design at Entry6.10.5 Entry Angle6.10.6 Entry Radius6.10.7 Entry Kerbing6.10.8 Entry Deflection6.10.9 Achieving Entry Deflection6.10.10 Visibility6.10.11 Circulatory Carriageway6.10.12 Inscribed Circle Diameter (ICD)6.10.13 Exits6.10.14 Crossfall and Longitudinal Gradient6.10.15 Segregated Right Turning Lanes6.10.16 Road MarkingsU-Turns - General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/60Safety At U-Turns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/60U·Turn Elements. .. . .. .. .. . . . . . ... .... ... . . . ... . . . . . . . . . . 6/606.13.1 .General6.13.2 Direct Taper Length6.13.3 Width of Physical Islands in the Median6.13.4 Left Turn Lane6.13.5 Median Openings6.13.6 Storage/Queuing length6.13.7 Merging Length6.13.8 Pavement Construction6.13.9 Road Lighting6.13.10 Traffic Signs and Road Markings6.13.11 Drainage and CrossfallUrban Road· Service Road Diverge/Merge , . 6/63Special Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/656.15.1 Residential Areas6.15.2 Older Residential Areas6.15.3 Other Road UsersSignalized Junctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6/686.16.1 Introduction6.16.2 Basic Requirements6.16.3 Typical Layout Features

Page C/3


SECTION 7Clause 7.1Clause 7.2

Clause 7.3

Clause 7.4

Clause 7.5

. SECTION 8Clause 8.1

Clause 8.2

Clause 8.3

Clause 8.4

Clause 8.5

January 1997

CONTENTS

INTERCHANGESIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7/1Types of Interchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7/17.2.1 General7.2.2 Full Interchange7.2.3 Compact Interchange

Selection of Junction Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7/67.3.1 General7.3.2 Traffic Flows and Design Year7.3.3 Junction Spacing within the Network7.3.4 Initial Information Requirements and Decisions7.3.5 Types of Interchange for Preliminary Design7.3.6 Preliminary DesignsDesign Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7/87.4.1 Definitions7.4.2 Design Speed7.4.3 Lane Provision and Capacity7.4.4 Hard Shoulders and Edge Strips7.4.5 Merges and Diverges at Interchanges7.4.6 Slip Roads7.4.7 Link Roads7.4.8 Loop Roads7.4.9 Weaving SectionsOther Design Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7/167.5.1 Clearance and Headroom7.5.2 Superelevation7.5.3 Safety Fencing7.5.4 Signing7.5.5 Lighting7.5.6 Utilities7.5.7 Emergency Vehicles7.5.8 Maintenance Provisions7.5.9 Environmental Issues

DRAINAGEIntroduction. ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/18.1.1 Functions of Highway Drainage8.1 .2 Minor and Major SystemsDesign Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/28.2.1 Hydrological Data8.2.2 Design Return Period8.2.3 Design MethodUrban Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/148.3.1 Introduction8.3.2 Urban Catchment8.3.3 Positive Drainage8.3.4 Drainage of the Carriageway8.3.5 Drainage of Medians, Footways and Verges8.3.6 Emergency Flood Area (EFA)8.3.7 Maintenance StrategyRural Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/188.4.1 Introduction8.4.2 Rural Catchment8.4.3 Drainage of the Carriageway8.4.4 Drainage of Medians and Verges8.4.5 Natural Surface DrainageJunction Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/228.5.1 Introduction8.5.2 Drainage at Junctions

Page C/4

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SECTION 9Clause 9.1

Clause 9.2

Clause 9.3

Clause 9.4

Clause 9.5

Clause 9.6

Clause 9.7Annex 9A

CONTENTS

Subsurface Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8/258.6.1 Introduction8.6.2 Subsurface Drainage Methods

PAVEMENTIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9119.1.1 General9.1.2 Typical Pavement Structures9.1.3 Road Deterioration9.1.4 Variability in Materials and Road PerformanceTraffic Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9/29.2.1 Introduction9.2.2 Design Life9.2.3 Traffic Forecasting9.2.4 Traffic Counts9.2.5 Standard Axles9.2.6 Determination of Cumulative Standard Axles9.2.7 Design Traffic ClassesPavement Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9/69.3.1 Qatar Construction Specification (QCS)9.3.2 SUbgrade9.3.3 Granular Material for Sub-base and Roadbase9.3.4 Roadbase - Asphalt Concrete9.3.5 Cement Bound Material9.3.6 Wearing Course9.3.7 Concrete for Rigid Pavements9.3.8 Precast Paving BlocksDesign Charts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9/89.4.1 General9.4.2 Asptialt Concrete Roadbase9.4.3 Asphalt and Granular Roadbase9.4.4 FleXible-Composite Roadbase9.4.5 Reinforced Jointed Concrete Slabs9.4.6 Precast Block PavingSpecial Pavement Sections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9/159.5.1 Staged Construction (Single Layer Construction)Pavement Evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9/159.6.1 Introduction9.6.2 Routine Monitoring9.6.3 Detailed Survey9.6.4 Detailed Investigation9.6.5 Interpretation and Design of Remedial WorksReferences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9118Basis of the Design Method for Asphalt Roadbase . . . . . . . . . . . . 9/199A.1 Design Methods9A.2 Design Strategy9A.3 Applicable Methods9A.4 Specific Method for Qatar9A.5 Weak Subgrades9A.6 References

SECTION 10Clause 10.1

Clause 10.2

January 1997

ROADWAY LIGHTINGIntroduction .10.1.1 Reasons for Lighting10.1.2 Justification10.1 .3 Scope10.1.4 Complementary StandardsPerformance Requirements .10.2.1 Summary of Road Classifications in Qatar10.2.2 Lighting Performance Recommendations10.2.3 Limitation of Glare and "Light Pollution"

10/1

10/1

Page CIS


GUIDANCE NOTES TO PREPARE A BRIEF FOR GEOTECHNICALSITE INVESTIGATIONSIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B/1Initial Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B/1Preparation of the Brief. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B/2B3.1 Geotechnical Investigation WorksB3.2 Field TestsB3.3 Laboratory TestsEngineering Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B/7B4.1 Methods of InvestigationB4.1.1 Trial PitsB4.1.2 BoreholesB4.1.3 SamplesB4.2 TestingB4.2.1 In Situ TestingB4.2.2 Laboratory TestingB4.3 EarthworksB4.4 Retaining StructuresB4.5 Geo-syntheticsSample Pro Forma for Quantifying Geotechnical Site Investigations B/14

Clause 10.3

Clause 10.4Clause 10.5

Clause 10.6

APPENDIX AClause A1CiauseA2

Clause A3

CiauseA4CiauseA5

APPENDIXB

Clause B1Clause B2Clause B3

Clause B4

Clause B5

Recommended Practice .10.3.1 Decisions Prior to Design10.3.2 Standard Lighting Geometries for Different Road Profiles10.3.3 Lighting Columns as Hazards10.3.4 Typical Lighting Layouts at JunctionsSpecification of Equipment .Electrical Distribution .10.5.1 Supply10.5.2 Feeder Piliars10.5.3 Cables10.5.4 Ducts10.5.5 Earthing Systems10.5.6 Safety StandardsMaintenance and Operation .10.6.1 Design Implications10.6.2 Quality of Equipment10.6.3 Inventory and Fault Reports10.6.4 Cleaning and Lamp Replacement10.6.5 Frequency of Inspections10.6.6 Hours of Operation

SURVEYSIntroduction .Survey in Qatar .A2.1 Centre for GiS - Mapping and Positioning ServicesA2.2 Land Information Centre - General Survey Section (GSS)A2.3 Planning DepartmentA2.4 CEO Survey UnitSurvey Work Procedures .A3.1 Topographical SurveysA3;2 Services SurveysA3.3 As-built SurveysApproved Survey Companies .Specification for Topographical Survey .A5.1 Features to be ObservedA5.2 Preparation of Survey DataA5.3 SpecificationsA5.4 Checking and Verification

CONTENTS

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10/710/7

10/8

Al1AI1

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Al6Al6

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January 1997 Page C/6


GLOSSARY OF TERMS USED

GLOSSARY

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AADT(Average Annual Daily Traffic) - Totalyearly two-way traffic volume divided by thenumber of days in the year.

Acceleration Lane - A speed change lane toenable a vehicle entering a roadway to increaseits speed to merge with through traffic.

Access Road - Road providing access to alocal area or individual properties from adistributor road.

ADT (XX) (Average Daily Traffic) - The currentor projected average two-way.daily traffic for theyear 19xx or 20xx used to define the traffic forthat year in the Gregorian Caiender.

At-grade Intersection - An intersection whereall carriageways join or cross at the same level.

Auxiliary Lane - The portion of the carriagewayadjoining the travelled way for weaving, truckclimbing, speed change, or for other purposessupplementary to through traffic movement.

Axle Load - The total load transmitted by allwheels on a single axle extending across thefull width of the vehicle. Tandem axles 1marless apart shall be considered as a single axle.

Backslope - In cuts, the slope from the bottomof the ditch to the top of the cut.

Berm - (1) A raised and elongated area of earthintended to direct a flow of water, screenheadlight glare. (2) Embankment widening toprovide lateral support for the roadway.

Braking Distance - The distance required tostop the vehicle from the instant brakeapplication begins.

Braking Reaction Distance - The distancetraversed by the vehicle from the instant thedriver sights an object necessitating a stop, tothe instant the brakes are applied.

Bridge - Structure supporting road orpedestrian walkway over an area to be crossed.

Broken Back Curve - An arrangement ofcurves in which a short tangent separates twocurves in the same direction.

January 1997

Buffer Zone (Buffer Strip) - Land adjacent toa highway acquired by the highway authority forthe purpose of preventing development thatwould be adversely affected by traffic noise, orfor erecting noise barriers.

Business District - That portion of amunicipality or an area within the influence of amunicipality in which the dominant land use isoffices, banks, hotels and government bUildings

California Bearing Ratio (CBR) - The ratio ofthe force required to penetrate a soil mass witha circular piston of 5cm diameter to the forcerequired to penetrate a mass of high qualitycrushed stone with the same piston. The rate ofpenetration in both cases is 1.27mm perminute. Refer BS 1377.

Camber - (1) A slight arch designed or built intoa structure to compensate for the naturardeflection after loading. (2) Siope on a singlecarriageway road from the centre to the edgesto aid drainage.

Capillary Break Layer - The layer of specifiedor selected material placed on the subgrade tobreak the capillary rise of water and salts.

Capping Layer - Layer replacing existingmaterial under the pavement.

Carriageway - The part of a highway, includingshoulders, for vehicular use. Singlecarriageway or dual carriageway.

Catchment - Area feeding rainfall to a specificpoint.

Centreline - (1) For a two-lane highway thecenterline is the middle of the travelled way,and for a divided highway the centreline may bethe centre of the median. For a dividedhighway with independent roadways, eachroadway has its own centreline. (2) The definedand surveyed line shown on the plans fromwhich the highway construction is controlled.

Cloverleaf Interchange A four-leginterchange with loops for left turns, and otherconnections for right turns. A full cloverleaf hasramps for two turning movements in eachquadrant.

Page G/1


Commercial Area - That portion of amunicipality or an area within the influence of amunicipality in which the dominant land use isshops and commercial business.

Crash Barrier - See Safety Fence

Crest Vertical Curve - A vertical curve havinga convex shape in profile.

Crossfall - (1) A pavement superelevatedtoward the right or left shoulder on appreciablecurves. (2) On divided highways on straightsor flat curves, each one-way pavement mayhave a unidirectional slope across the entirewidth of pavement, usuaily downward towardthe outer edge.

Culvert - A closed conduit, other than a bridge,which conveys water carried in a naturalchannel or waterway from one side of ahighway to the other side. Culverts may beprefabricated pipes of concrete, steel, or vitrifiedclay, or they may be cast-in-place structures ofreinforced concrete, such a box culverts or archculverts.

Curve Widening - The widening of the highwaytraveiled way on sharp curves to compensate

. for the fact that the rear wheels of a vehicle donot foilow exactly in the tracks of the frontwheels.

Deceleration Lane - A speed-change lane thatenables a vehicle to slow to a safe exit speedwhen making an exit turn.

Desert Road - A graded track to access a farmor small group of properties.

Design Hour Volume (DHV) - Th.e future twoway hourly traffic volume for use in design,usuaily the 30th highest hourly volume of thedesign year (30 HV).

Design Lane - The lane on which the greatestilumber of equivalent 8-tonne, standard axleloads is expected. Normaily, this will be eitherlane of a two-lane highway (single carriageway)or the outside lane of a multilane highway (dualcarriageway).

Design Life - The number of years of intendedservice life of a facility before the first majorrehabilitation.

Design Speed - A speed selected for purposesof design and correlation of the geometricfeatures of a highway and a measure of thequality of service offered by the highway. It is

January 1997

GLOSSARY

the highest continuous speed where individualvehicles can travel with safety upon a highwaywhen weather conditions are favourable, trafficdensity is low and the geometric designfeatures of the highway are the governingconditions for safe speed.

Design Vehicles - Selected motor vehicles withthe weight, dimensions, and operatingcharacteristics used to establish highway designcontrols for accommodating vehicles ofdesignated classes.

Design Year - The future year used to estimatethe probable traffic volume for which a highwayis designed. A time 10 to 20 years from thestart of construction is usually used.

Diamond Interchange - A four-leg interchangewith a single one-way ramp in each quadrant.Ail left turns are made directly on the minorroadway.

Distributor Road - A type of road serving twodistinct functions. It provides a traffic servicebetween primaries, arterial-coilectors, otherlocal roads, a town, viilage, industrial orcommercial deveiopment, or a recreationalarea. it also provides direct vehicular access toprivately owned properties. Land service is thefirst consideration, but traffic service may havemore than incidental significance.

Ditch - A trench dug in the earth for drainagepurposes.

Diverging - The dividing of a single stream oftraffic into separate streams.

Dual Carriageway - A highway with separatedcarrlageways for traffic in opposite directions.

Eighty-fifth Percentile Speed - The speed ator below which 85 percent of the vehicles arebeing operated.

Elevated Highway - A highway on fiil orstructure above the level of the adjacentground.

Embankment - A raised earth structure onwhich the road is placed.

Emergency Vehicle - A vehicle belonging tothe armed forces, civil defence, police, fireservice or ambulance service, or otherdesignated vehicle used for answeringemergency calls for assistance.

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Emergency Flood Area (EFA) - Area set asideto store flood water during heavy rainfall.

ESA (Equivalent Standard Axle) - The effecton pavement performance of any combinationof axle loads of varying magnitude, equated tothe number of reference single-axle loadsrequired to produce an equivalent number ofrepetitions of an 8-tonne single axle.

Exit - The point where traffic leaves to travel toan intersecting road.

Fencing· Item placed next to the road to definethe edge of reservation or restrict animalaccess.

Foreslope - The slope from the edge of thesurfaced shoulder to the top of the subgrade, orthe bottom of the ditch in cuts.

Formation - Graded surface above sUbgrade orcapping layer on which the pavement structureis laid.

Formation Drain - Porous or perforated pipe,or graded aggregate installed under a roadwayor shoulder to provide subsurface drainage.

Footpath - That portion of a street or highwaybetween the kerb line or edge of the roadway,and the adjacent edge of reservationconstructed specifically for pedestrians(sometimes referred to as sidewalk).

Full Overtaking Sight Distance (FOSD) - Theminimum sight distance that must be availableto enable a driver of one vehicle to passanother vehicle safely without interfering withthe speed of an oncoming vehicle travelling atthe design speed.

Gantry - Signal or sign support above acarriageway.

Ghost Island - Painted or hatched marking onthe road surface to gUide traffic.

Gradient - The profile of the centre of thecarriageway, or its rate of ascent or descent.

Grade - To shape or reshape earth by means ofcutting or filling.

Grade Separation - A structure that providesfor highway traffic to pass over or under anotherhighway.

Gully - Collection and distribution point forsurface water along a gutter.

January 1997

GLOSSARY

Gutter - A paved and generally shallowwaterway provided for carrying surfacedrainage.

Headwall - A vertical or inclined wall at the endof a culvert to prevent earth from spilling intothe channel.

Hierarchy Classification - The grouping ofindividual highways in a highway system,according to their purpose or function, the typeof traffic they serve, and their maintenancerequirements. The main functional classes arePrimary, Secondary, and Tertiary, thoughsubclasses are also used.

Highway - see Road.

Horizontal Alignment - Horizontal geometry ofthe highway.

Horizontal Curve - A circular curve or transitionby means of which a highway can changedirection to the right er left.

Independent Alignments - Each carriagewayof a dual carriageway is designed and locatedto take full advantage of the terrain. Themedian need not be of uniform width, and thetwo carriageways need not be at the samelevel.

Industrial Area - That portion within amunicipality in which the dominant land use islight or heavy industry.

Inside Lane - the first lane of a dualcarriageway, commonly referred to as the slowlane or nearside lane.

Interchange - A system of interconnectingroads in conjunction with one or more gradeseparations, providing for the movement oftraffic between two or more roads on differentlevels.

Intersection - The connection of two or moreroads is called a intersection.

Intervisibility - The requirement of a vehicledriver to see approaching vehicles and also forhis vehicle to be seen by approaching vehicles.

Junction - Treatment of the intersection of tworoads.

Kerb - A structure with a vertical, horizontal orsloping face placed along the edge of apavement or shoulder forming part of a gutter,and strengthening or protecting the edge..

Page G/3


Lane - A portion of the travelled way providingfor a single line of traffic in one direction.

Left Lane - On a two-lane, two-way road, thetraffic lane that is to the left of the centreline andnormally used by traffic moving in the oppositedirection; or on a multiiane road, the extremeleft traffic lane of those avaiiable for traffictravelling in the same direction, ie: adjacent tothe median.

Left-Turn Lane - A traffic lane within the normalsurfaced width of a roadway or an auxiliary laneadjacent to or within a median, reserved for leftturning vehicles at an intersection.

Median - The portion of a divided highwayseparating the travelled ways of traffic travellingin opposite directions.

Median Barrier - A longitudinal system used toprevent an errant vehicle from crossing themedian of a dual carriageway.

Median Opening - A gap in a median providedfor crossing and turning traffic.

Merging - The converging of separate streamsof traffic into a single stream.

Moisture Content - The percentage, by weight,of water contained in soil or other material,usually based on the dry weight.

Motorway - A multiiane, dual carriagewaydesigned to move large volumes of traffic athigh speeds under free-flow conditions.Motorways have full control of access withinterchanges incorporating grade separationand junctions.

Network - A group of roads of varied hierarchyin a defined area.

Noise Barrier - A barrier of earth, stone,concrete, or wood placed adjacent to thehighway to reduce the noise level on abuttingproperty.

One-way Highway - A highway or roadwayhaving one or more lanes on which all vehiculartraffic must go in the same direction.

Outer Separator - A separator between aservice road and the carriageway of a highwayor major street.

Outside Lane - The lane nearest the median ona dual carriageway, commonly referred to asthe fast lane or off-side lane.

January 1997

GLOSSARY

Overpass - A grade separation where thehighway passes over an intersecting highway.

Parking Lanes - Additional width outside thetravelled way of a highway or street that isdesignated for the temporary storage ofvehicles.

Pavement - Structure on which vehicles travel.

Pedestrian Crossing - Any portion of a road atan intersection or elsewhere distinctly indicatedfor pedestrian crossing by signs, lights and bylines or other markings on the road surface.

Perception Time - The time required by adriver to perceive that he must change speed orstop.

Primary Road • Principle road within thenetwork.

Profile - A longitudinal section of a highway,drainage course, etc.

Ramp - A short carriageway, usually one way,to accomplish transfer movements within aninterchange from the arterial highway ormotorway to the minor road. Commonlyreferred to as a slip road.

Reaction Time - The time required for a driverto apply foot pressure to the brake after heperceived that he must stop.

Refuge Island - An island in a wide intersectionto provide refuge for pedestrians.

Residential Area - That portion of amunicipality, or an area within the influence of amunicipality in which the dominant land use isresidential development, but where smallbusiness areas may be included.

Rest Area - A roadside area with parkingfacilities separated from the carriagewayproviding motorists with opportunities to stopand rest for short periods.

Reverse Curve - A curve consisting of two arcsof the same or different radii curving in oppositedirections and having a common tangent ortransition curve at their point of junction.

Right-Turn Lane - An auxiliary lane ordesignated lane provided at intersections forright-turn movements.

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Ring Road - An arterial highway for carryingtraffic around an urban area or portion thereof.

Road (Highway) - A general term denoting apublic way for purposes of vehicular travelincluding the entire area within the reservation.

Roadbase - The layer of specified or selectedmaterial placed on a sub-base or formation.

Road Hump (sleeping policeman) - Raisedportion of the carriageway designed to slowpassing vehicles.

Road Markings - A traffic control deviceconsisting of lines, patterns, works, symbols, orcolours on the pavement, or adjacent to theroad.

Road Sign - A traffic control device mounted ona support above the level of the roadway thatconveys a specific message by means of wordsor symbols.

Road Stud - Reflective or nonreflective stud onthe road surface to define road markings andtraffic positioning.

Rumble Strip - A rough textured surface,constructed for the purpose of causing the lyresof a motor vehicle driven over it to vibrateaudibly as a warning to the driver.

Safety Fence - A protective cable, beam or walldevice placed along the carriageway edge forthe purpose of redirecting vehicles that have leftthe roadway at a point of hazard.

Sag Vertical Curve - A vertical curve having aconcave shape in profiie.

Screening - The use of trees, shrubs, fences,or other materials to obscure an objectionableview or to reduce an objectionable sound.

Secondary Road - A highway of less nationalsignificance than a Primary road, but a highwaythat is intended to move large volumes of trafficat high speeds. Military installations andseaports not served by a Primary road arereached via Secondary roads. Trafficmovement is the primary consideration, but thistype of road may also provide some landservice function.

January 1997

GLOSSARY

Separator - An area or a device locatedlongitudinally between two carriageways so asto separate traffic flowing In the same oropposite directions, and so designed as todiscourage or prevent passage by vehicles fromthe traffic lanes on one side of the separator tothose on the other.

Shoulder - The portion of carriagewaycontiguous with the travelled way foraccommodation of stopped vehicles foremergency use, and for lateral support of baseand surface courses.

Shy Distance - The portion of carriagewaycontiguous with the travelled way whichseparates the face of the kerb from the travelledway.

Sight Distance - The length of roadway ahead,visible to the driver.

Standard Axle - Single axle load of 8,167 kg.

Stopping Sight Distance (SSD) - The distancerequired by a driver of a vehicle, travelling at agiven speed, to bring his vehicle to a stop afteran object on the roadway becomes visible. Itincludes the distance travelled during theperception and reaction times, as well as thevehicle braking distance.

Storm Drain (sewer) - A system of catchbasins and underground conduits collecting,concentrating, and conveying water to adisposal point.

Street - See Road.

Sub-base - The layer or layers of specified orselected material of designed thickness placedon the subgrade to support the roadbase.

Subgrade - (1) The top 300mm layer ofembankments or excavated areas on which thepavement structure including shoulders isconstructed. (2) The top of a capping layerupon which the pavement structure andshoulders are constructed.

Superelevation - The elevating of the outsideedge of a curve to partially offset the centrifugalforce generated when a vehicle rounds thecurve.

Superelevation Runoff (application) - Thetransition distance between normal crown andfully superelevated roadway.

Page GIS


Tack Coat - An application of bituminousmateriai to an existing surface to provide bondwith a superimposed course.

Time of Concentration - The time required forstorm runoff to flow from the most remote pointof a drainage catchment area to the point underconsideration. It is usually associated with thedesign storm.

Toe of Slope - The intersection of anembankment side slope with the original groundsurface.

Topsoil (Rodah soil) - Surface soil, usuallycontaining organic matter.

Traffic Barriers - Roadside barriers, medianbarrie.rs, crash cushions, and bridge parapetsintended to guide or protect traffic from roadsidehazards, including collision with other vehicles.

Traffic Island - An island provided in the roadto separate or direct streams of traffic; includesboth divisional and channelizing islands.

Traffic Lane - That portion of the travelled wayfor the movement of a single line of vehicles.

Traffic Signal· Lights used to direct and stopand start traffic.

Transition - A section of variable pavementwidth required when changing from one width oftravelled way to a greater or lesser width.

Transition Curve (Spiral) - A cLirve of variableradius intended to effect a smooth transitionfrom straight to curved alignment.

Travelled Way - The portion of thecarriageway for the movement of vehicles,exclusive of shoulders, hard strips, shydistances and auxiliary lanes.

Turning Lanes - Auxiliary lanes provided at at-grade intersections for right and left turningmovements.

Turning Track Width - The radial distancebetween the turning paths of the outside of theouter front tyre and the outside of the rear tyrethat is nearest the center of the turn.

Typical Cross Section - A transverse sectionof a proposed highway showing the lateraldimensions and functional and structuralelements of the highway.

January 1997

GLOSSARY

Underpass - A grade separation where thehighway passes under an intersecting highway.Can be a pedestrian or animal underpass whichcrosses under the main highway.

Verge' The portion of the highway reservationthat is next to the road and is unpaved.

Vertical Curve - A curve on the longitudinalprofile of a road to provide a change of gradient.

Visibility - The distance at which an object canbe just perceived by the eye.

Visibility Splay· The area required for drivervisibility to the left and right on the approachto a junction from the minor arm.

Wearing Course· The top layer of a pavementwhich resists skidding, traffic abrasion and thedisintegrating effects of climate.

Weaving - The crossing of traffic streamsmoving in the same general directionaccomplished by merging and diverging.

Weaving Sections - Highway segments wherethe pattern of traffic entering and leaving atcontiguous points of access resuits in vehiclepaths crossing each other.

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ROAD SYSTEM IN QATAR

The Highway Network

Roads within the State of Qatar each fulfilcertain functions within the overall network. Ahierarchy exists which defines their variousroles. Table 1 shows the status of road typeswithin the hierarchy.

Primary Routes

These are 'routes of strategic significancewhose purpose is to act as the principaldistribution routes between the City of Doha, themain regional centres and the national border.They are generally dual carriageway roads, builtto high geometric standards.

The present system of Primary Routes isillustrated in Figure 1 and Figure 2.

Secondary Routes

Secondary Routes serves as area distributorsby linking Primary Routes either to each otheror by feeding traffic into the Tertiary Routenetwork. They are generally dual Carriagewaybut in rural areas may be single carriageway.

The major Secondary Routes are also shown inFigure 1 and Figure 2.

Tertiary Routes

District distributors, local distributors and accessroads are classified as Tertiary Routes. Districtdistributors are urban dual carriageway roadsproviding high capacity routes between districts.Local distributor roads link access roads toeither the Secondary Route network or, in urbanareas, the district distributors. Both localdistributors and access roads arecharacteristically low design speed, singlecarriageway roads.

The Route Classification

The Route numbering system is centred on thecity of Doha. As shown in Figure 2, the origin ofthe Primary Route network is the D-Ring Road,this being designated Route No.1. The PrimaryRoutes Nos. 1 to 7 extend radially outwardsfrom the D-Ring Road. With the exception ofRoute No. 59, linking Route No.5 to the nationalborder, all Primary Routes have single digitnumbers.

January 1997


Secondary and Tertiary Route Numbers followa branching system based on the PrimaryRoute Numbers.

Qatar Area Zones

For ease of communication and coordinationbetween Government bodies Qatar has beendivided into reference Zones.

Activities such as planning, street names, RoadNetwork Plans and Hierarchy Plans aregenerally referenced against the area zones.These zones are illustrated in Figure 3 andFigure 4.

Page RSQ/1

QATAR HIGHWAY DESIGN MANUAL ROAD SYSTEM IN QATAR

•Route Classification Class Function Carriageways General Design

Ref CorridorWidth

(m)

PRIMARY ROUTE

Rural P1 A major road linking lowns, or a Dual 2·3 lane 64 Roundabouts, minor T or grade-bypass separated junctions. Some U-

turns on rural routesUrban P2 A major urban road

SECONDARY ROUTES

Rural S1 A rural road linking settlements Dual 2·3 lane 64/40 T-juncUons, with double U·turns10 the primary networks. Single 2-lana on dual carriageway, staggeredSignificant traffic flow or use by junctions on single carriagewaygoods vehicles

Urban S2 A major urban road lor through Dual 2·3 lane 64/40/32trafflc

TERTIARY ROUTES

Rural Local Road TR1 A rural road linking settlements Single 2-1ane 40/32 T-junclions

District Distributor TR2 An urban road linking districts Dual 2·3 lane 64/40/32 Roundabouts, slip-onlslip-off orwide single or signalised junctions. No U-turns.single 2-lane Limited access from existing

properties. New properties toprovide rear access. Parallelparking in bays

Local Distributor TR3 A road distributing traffic within Wide single or 40/321241 Roundabouts. T·junctions ora district single 2-lane 20 signalised junctions. Offset X-

(some existing roads. Direct access fromroutes may be properties. Parallel parking bays.dualcarriageway)

Access Road TR4 A road giving direct access to Single 2-lane 24/20/16 Roundabouts or T-junctions.properties Offset X-roads. Direct access- residential major access from properties. Parallel parking,- residential minor access on street.- eul-pe-sac serving a maximum0112 properties

Service Road TRS A road giving direct access to Single 1·way Merge/diverge tapers onto dualproperties and collecting minor or 2·way clway. Parallel alignment to majorroads for entry/exit onto Dual road way. T·Junction access forCarriageway. Minor roads. Speed reduction,

direct access from properties, on-street parking, parallel or angle.

SPECIAL ROUTES (2)

Scenic Routes SR1 Roads with special functions as varies varies Varies, emphasis on integrateddignitary routes or recreational landscaping and architecture.routes

Lorry Routes (3) SR2 Specially designated and varies varies Varies, emphasis on pavementdesigned for heavy vehicles design, appropriate junction radii

etc.

Notes (1) The general road corridors are based on the MMAA's plan "General guidance for road cross-sections and utility dispositions".(2) These can be either primary, secondary or tertiary routes.(3) The main Lorry Routes include the Regional Primary Roads and the Rural Distributors.

Table 1 Route Classification and Function

January 1997 Page RSQ/2

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Figure 1 Road Hierarchy - State of Qatar


N

A

PRIMARY ROUTES

SECONDARY ROUTES

TERTIARY ROUTES

LOCAL ROUTES

For HierarchyInside Doharefer to PageRSC/4

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)

Figure 2 Road Hierarchy - Greater Doha

rROAD SYSTEM IN QATAR

N

A

KEY

_ PRIMARY ROUTES

_ SECONDARY ROUTES

_ TERTIARY ROUTES

LOCAL ROUTES

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•QATAR HIGHWAY DESIGN MANUAL ROAD SYSTEM IN QATAR

N

A

.'

___ ZONE BOUNDARY

ZONE NUMBER

75

•

94

74

•

71

80

95

76

82

78

72

85

83

96

84

86

•

•

Figure 3 QARS Zones - State of Qatar


•

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N

A

ZONE BOUNDARY

5. ZONE NUMBER


57


Figure 4 OARS Zones - Greater Doha


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ZONE

No. Name

1. AI Jasra

2. AIDiwan

3. Mohammed Bin Jasim

4. AI Asmakh

5. AI Najada

6. AI Ghanim AI Qadaem (North)

7. New Markets

8.

9.

10. Wadi AI Sail (East)

11. AI Rumeila (East)

12. AI Bidda

13. Musheireb

14. Abdul Aziz

15. AI Doha AI Jadeeda

16. AI Ghanim AI Qadeem (South

17. Al Hitmi

18. AI Salata

19. Doha Port

20. Wadi AI Sail (West)

21. AI Rumeila (West)

22. Bin Mahmoud (North)

23. Bin Mahmoud (South)

24. AI Muntazah

25. AI MansouraiBin Dirham

26. Najrna

27. Umm Ghuwailina

28. AI Khulailat

29. Ras Abu Abboud

30.

January 1997


ZONE

No. Name

31.

32. Madina! Khalila (North)

33. AI Markhiya

34. Madina! Khalila (South)

35. Kulaib

36. AI Muraur I AI Massila

37. Bin Omran / AI Hitmi I AI Jadeed

38. AI Sadd

39. AI Mirqab I AI Nasr

40. AI Asiri I AI Salata I AI Jadeeda

41. AI Hilal (West)

42. AI Hilal (East)

43. AI Nuaija (West)

44. AI Nuaija (East)

45. AI Matar AI Qadeem

46.

47.

48. Doha International Airport

49.

50.

51. AI GharrafaiBani Hajer/AI Zaghwa

52.

53. AI Rayyan AI Jadeed/Muai!her North

54.

55 AI Soudan Sou!hlAI AZiziyaiAIGhanim/Al Murrah

56. AI Khulaifat AI Jadeeda

57.

58.

59.

Page RSQI7


ZONE

No. Name

60. New District of Doha (West Bay)

61. Diplomatic District







68.

69. New District of Doha 69

70. AI Kheesa

71. Umm Sial I AI Kharaitiyat

72. AI Utouriya

73. AI Jemailiya

74. Ai Khor

75. Ai Thakhira

76. AI Ghuwairiya

77. FuwairitiAI Jassasiya

78. Abu Dhaiouf/Ai Zubara

79. Madinat AI Shamall AI Ruwais

80. Ai Shahhniya

January 1997


ZONE

No. Name

81. Abu Nakhla

82. Rawdat Rashed

83. MUkainess

84. Umm Bab

85. AI Nasraniya

86. Dukhan

87.

88.

89.

90. AI Wakra

91. Al Wukair

92. Mesaieed (Town)

93. Mesaieed (Industrial Area)

94. Shaqra

95. AI Kharrara

96. Abu SQmra

97. Sawda Natheel

98. Khor AI Adaid

Page RSQ/8

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SECTION 1

relaxations and departures and specialconsiderations

All reference to speed in this manual should betaken as the design speed unless notedotherwise.

Design speeds for Special Roads (ClassReference SR1 and SR2) require specialconsideration and should be agreed with theDirector of Civil Engineering.

RELATED

Design Speed for VariousRoad Classifications.

DESIGN SPEEDPARAMETERS

Parameter Reference

Posted Speed Clause 1.4Table 1.3

Stopping Sight Clause 2.2Distance Table 2.1

Overtaking Sight Clause 2.3Distance Tabie 2.2

Horizontal Clause 3.2Curvature Table 3.1

Vertical Curvature Clause 4.3Table 4.4.3

Traffic Calming Clause 1.9

Table 1.1

1.2

Class Type of Highway DesignReference Speed

(kph)

Primary RoutesP1 Rural 140P2 Urban 120

Secondary RoutesS1 Rural Distributors 140S2 Urban Distributors 100

Tertiarv RoutesTR1 Rural Local Road 100TR2 District Distributor 100TR3 Local Distributor 70TR4 Major IMinor Access 60TR5 Service Roads 60

The driver will vary his speed according to hisimpression of the road alignment and layout.Table 1.2 details the main design speed relatedparameters which are dealt with in greaterdepth in their respective clauses in this manual.

SECTION 1 DESIGN SPEED

The speed of vehicles depends on thecapabilities of driver and vehicle and on othergeneral conditions such as the physicalcharacteristics of the highway and its roadsides,the weather, the presence of other vehicles andfinally, the presence of speed limitations.Although anyone of these may govern, oftenthe effects are combined.

In Qatar the weather has an adverse effect onthe relationship between lyre and road surfaceand hence design speed. The heat results in abuild-up of rubber deposit on the road surfacefrom tyres. This in turn decreases the skidresistance of the road surface. Qatar is alsosubject to intense rainfall at certain times of theyear. The addition of rainfall to a road surfacewhich has reduced skid resistance increasesthe potential for accidents. This is particulariyvalid on the approach to and at junctions whereturning and stopping movements are high.Furthermore, water is often spilled from watertankers at roundabouts and junctions. Bearingthis in mind, the selection of design speed andhence stopping distance is extremeiy important.

The design speed of a highway may be definedas the highest continuous speed at which anyvehicle can safely travel when given favourableweather conditions and low traffic volumes, sothat the design features of the highway maygovern. Such design features may includestructures, or frequency of junctions. Thedesign speed is related to the posted speedwhich represents the 85 'h percentile of thedesign speed, that is the value at which 15% ofvehicles are expected to exceed the designspeed. Refer to Section 1.4 for posted speeds.

The road alignment shall be designed so as toensure that standards of alignment, visibilityand superelevation are consistent with theselected design speed. This choice willessentially be dependent on the provision of thehighway and its location, I.e. single or dualcarriageway or whether in a rural or urban area.The visibility criteria are dealt with in Section 2Sight Distance.

The design speed for various roadclassifications are shown in Table 1.1. Theroad classifications are defined in the front ofthis manual, refer to Road System in Qatar.

1.1 GENERAL


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The selection of design speed should beapproved by the Director of Civil EngineeringDepartment. Refer to Clause 1.8 and 1.9 for

Table 1.2 Design Speed Related Parameters

January 1997 Page 1/1


1.3 SELECTION OF DESIGN SPEED 1.6

SECTION 1

CONNECTION TO EXISTING ROADS •The designer must select the appropriatedesign speed based on his knowledge of theclass of highway planned, the character ofterrain, development density, traffic volumesand economic considerations. Generally forQatar the design speed is selected using Table1.1.

Design speeds shall also be selected withreference to the posted speed limit envisagedor that which is already in place for the road andthe Road Network Plan. An allowance shall bemade for a margin of safety for vehicles whichwill travel in excess of the speed limit. Refer toSection 1.4 below.

Care shall be taken where an improved sectionof road rejoins an existing road. The existingstandard of curvature and sight distance at theinterface shall be subject to the samerestrictions as would be relevant for the designspeed of the Improvement. Carefulconsideration shall also be given for roadspassing between rural and urban areas, postedspeed step down and also dual to singlecarriageways, although this latter case shouldbe limited to junction locations only.

In all cases it is important to emphasise theneed for clear signing at any location wherethere is a speed reduction.

•PARAMETEROFSELECTION

VALUES1.7

Generally for Qatar the design speed isselected using Table 1.1. In certaincircumstances it may be uneconomic to designan alignment to the prescribed standards andconsequently a reduced standard may be used.This is termed a "relaxation". In situations ofextreme difficulty where application of arelaxation does not overcome the difficulty, itmay be possible to overcome them by adoptionof departures from standard. Any suchrelaxations or departures must be agreed inwriting with the Director of Civil Engineering.

1.8 RELAXATIONS AND DEPARTURES

Designers should normally aim to achieve thedesirable minimum values for stopping sightdistance, horizontal curvature and vertical crestcurvature. For sag curves, designers shouldnormally aim to achieve at least minimumvalues.

Relationship between DesignSpeed and Posted Speed

POSTED SPEED

Design Speed Posted(kph) Speed (kph)

140 120120 100100 8080 6070 6060' 50 or less'".

1.4

Table 1.3

The above table allows for a margin of safetyappropriate to the selected design speed.

Posted Speed is the mandatory speed limitapplied to a road. The speed limit is displayedon the roadside and is enforceable. The postedspeed limits to be implemented in relation todesign speed are shown in Table 1.3 below.

Special consideration required for[ower class roads, see Clause 1.9

1.5 CHANGEOVER OF DESIGN SPEED

Transitions between roads (or sections of aroad) with different design speeds shall becarefully implemented so as not to present thedriver with an abrupt change in standards. Fordetails of signing the speed reduction refer tothe Qatar Traffic Manual.

Where an alignment changes from a higher tothe next lower design speed, relaxations belowthe desirable minimum radius and desirableminimum stopping sight distance shall not beused at the start of the lower design speedsection.

Table 1.4 shows the allowable relaxation ofdesign speed for the different classes of roadsin Qatar.

The road classifications for Qatar and Doha aredescribed in the front of this manual. Theselection of a design speed is particularlydifficult for some of the roads in the older areasof the city. These areas are not so easilyclassified into land use and factors such asaccess and parking need to be assessed indetermining the design speed. Otherconsiderations are the number and spacing ofjunctions on a particular section of road.Relaxations and departures provide a means ofaccommodating these areas.



Class Type of Highway DesignReference Speed (kph)

Primary RoutesP1 Rural 140-120P2 Urban 120-100

Secondary RoutesS1 Rural Distributors 140-120S2 Urban Distributors 100

Tertiary RoutesTR1 Rural local Road 100TR2 District Distributor 100-70TR3 Local Distributor 80-60TR4 Major Access 60-50TR5 Seryice Roads 60-30

•

Table 1.4 Design Speeds for VariousRoad Classifications.

SECTION 1

Traffic calming measures may be introduced onexisting roads to reduce traffic speed. This isachievable by the use of narrow· lanes,chicanes, width or height restrictions, speedbumps or different textures or colours ofpavement.

Care shall be taken to ensure that trafficcalming measures, being introduced do notimpede emergency service vehicles.

A typical speed bump may be 305m in lengthwith its profile reaching a maximum of 100mm.They should ideally be located at 100mintervals. Much shorter intervals result ininconvenience to the residents, whereas formuch longer intervals the overall speed controlis lost. For safety reasons speed bumps shouldnot be located near junctions or sharp bends.

•

Departures below minimum values may beconsidered when cost or environmental savingsare considered to be significant, except in thefolloWing circumstances:

• immediately following an overtakingsection on single carriageway roads.

• on the immedia1e approach to ajunction, other than a roundabout,where frequent turning traffic will occur.

1.9 SPECIAL CONSIDERATIONS

Special consideration is required for residentialand commercial areas.

The posted speed in residential areas is 50kphfor local roads and lower for access roads.Lower speeds may be posted in specialcircumstances such as residential cul-de-sacsor in industrial areas where the facilities aredesigned to distribute vehicles to their finaldestination.

The lower design speeds applied in residentialand urban areas do not require superelevationon bends or other special dynamic relatedconsiderations.

One-way roads may be used for local andaccess roads usually in the form of discreetloops.

One-way roads should be designed so as not toencourage speeding. This may be achieved bythe use of narrow lanes and avoiding longstraight sections of road, and by implementinganyone or more of the traffic calming measureslisted below.

January 1997

For further details on traffic calming measures,refer to the Qatar Traffic Manual.

Page 1/3

•

•

2.2 STOPPING SIGHT DISTANCE


SECTION 2 SIGHT DISTANCE

b) Horizontal Plane

Measurement of Stopping SightDistance (SSD)

Full Overtaking Sight DistanceFOSD

Design Speed Full Overtaking(kph) Sight Distance (m)

140 910120 720100 58080 49070 41060 34550 29040 215

Figure 2.1

a) Vertical Plane

~2.:w 2.0m

1.05mO.26m

2.3 FULL OVERTAKING SIGHT DISTANCE

Full Overtaking Sight Distance (FOSD) is theminimum sight distance that must be availableto enable the driver of one vehicle to passanother vehicle safely and comfortably, withoutinterfering with the speed of an oncomingvehicle travelling at the design speed. In theinterests of safety and service, it is important toensure sufficient visibility for overtaking on asmuch of the road as possible. FOSD influencesthe average speed of the traffic especially whena highway is near operating capacity.

Table 2.2 shows for each design speed theFOSD required for overtaking vehicles using theopposing traffic lane on single carriageway.roads. These are minimum values andwherever possible, larger values should beused.

SECTION 2

Table 2.2

FOSD shall be measured from a driver's eyepoint between 1.05m and 2.00m above thecentre of the carriageway (for each lane in thecase of dual carriageways) as shown in Figure2.2 and shall be checked in both the horizontaland verticai planes.

Stopping Sight Distance SSD

Full Overtaking Sight Distance (forsingle carriageways only)

Design StoppingSpeed (kph) Sight Distance 1m)

140 350120 295100 21580 16070 12060 9050 7040 60

•

Sight distance is the continuous length of roadahead, visible to the driver, assuming adequateiight, visual acuity and clear atmosphericconditions. The arrangement of geometricelements is crucial to ensure adequate sightdistance exists for safe and efficient operation.There are two separate sight distances to beconsidered:

2.1 GENERAL

• Stopping Sight Distance (for all roads)

Safe stopping distance must be providedcontinuously on all highways. Safe overtakingdistance is appiicable only on two-lanehighways, primarily in rural or outlying urbanareas.

Stopping Sight Distance (SSD) is the distancerequired by the driver of a vehicie travelling at agiven speed to bring his vehicle to a stop afteran object on the carriageway becomes visible.SSD has three components; perception time,reaction time and braking time. A combineddriver perception and reaction time of twoseconds has been allowed for in Table 2.1.

Table 2.1

Stopping Sight Distance is measured from adriver's eye height of between 1.05 and 2.00mto an object height of between 0.26 and 2.00 m,above the road surface, refer Figure 2.1. Itshall be checked in both the horizontal andvertical plane between two points in the centreof the lanes on the inside of the curve (for eachlane in the case of dual carriageways).

•

..



FOSD is considerably greater than SSD andcan normally only be economically provided inrelatively flat terrain where the combination ofhorizontal and vertical alignment allows thedesign of a flat and relatively straight roadalignment.

Envelope of visibility

'~:~/"$H~efm

SECTION 2

central offset required with varying horizontalcurvature, in order to maintain the design speedrelated stopping sight distances. It can be seenthat extensive widening of verges andstructures, or medians with safety fence orsafety barriers, would be required to maintainstopping sight distances on horizontal radiibelow the minimum.

Figure 2.4 shows the maximum central offsetrequired with varying horizontal curvature, inorder to maintain the design speed related fullovertaking sight distance. It can be seen thatthe higher requirements of FOSD result inextensive widening of verges for all butrelatively straight sections of road.

•

Where possible on a single carriageway it isadvisable to design sections of road specificallyfor overtaking. This will reduce the frequency ofserious accidents occurring on 'roads withcontinuous large radius curves.

Figure 2.2 MeasurementOvertaking Sight(FOSD)

2.4 OBSTRUCTIONSDISTANCE

TO

of FullDistance

SIGHT


It is vital that drivers on an access or minor roadshould have adequate visibility on the approachto a junction with a major road. The drivershould have sufficient visibility to judge when tojoin the main carriageway. Furthermore, it isimportant for the driver on the major road to beaware of the vehicle approaching the junctionon the minor road.

The required visibility criteria for junctions isgiven in Section 6 Junctions.

The required visibility criteria should also beapplied to private accesses and drivewaysleading onto access roads.

•

The visibility required on bends is shown inTable 2.3 below. -

Visibility distance (m)Type of Road

Absolute DesirableMinimum Minimum

Local Roads 50 70Access Roads 30 50

Care shall be taken to ensure that nosubstantial fixed objects obstruct the sightlinesincluding road furniture, bridge piers, buildings,signs and cut slopes. However, isolated slimobjects such as lamp columns, sign supports, orother slim objects of width 550mm or under canbe ignored. Similarly, the effect of shortintermittent obstructions, such as bridgeparapets of minor roads under, can be ignored.Lay-bys or parking lanes should, whereverpossible, be sited on straights or on the outsideof curves, where stationary vehicles will notobstruct sightlines.

Table 2.3 Required Visibility on Bends forResidential Roads.

Sightlines should be checked where safetyfencing is installed.

2.5 EFFECT OF HORIZONTAL CURVESON SIGHT DISTANCE

Where there is likely to be increased pedestriantraffic, care must be taken to ensure thatvisibility is not impaired by pedestrians. Thiscould occur at the following residential andcommercial locations :

When a road is in a cutting or at bridgecrossings it will be necessary to widen vergesor increase bridge clearances to ensure that theappropriate stopping sight distance is notobstructed. Figure 2.3 shows the maximum

January 1997

•••

Pedestrian crossing points

Sikkas and alley-ways

Schools

Page 2/2


• • Shopping areas

SECTION 2

• Sports venues

• Cinemas

• Bus stops

In existing residential or' commercialdevelopments, it is important to review thevisibility on 90 degree bends. Where it is notpossible to achieve the required visibility,consideration should be given to using a largerradius or even locating a junction on the bend.

• Avoid building.on corner plots

In new developments where it is not possible toavoid the use of a 90 degree bend, the foilowingshould be considered:

• • Use low landscaping

•

• Avoid placing street furniture andsigning within the visibility splay.

Care should also be taken when locating.parking areas as parked cars wiil impedevisibility at tight bends, junctions and drivewaylocations. Refer to Section 5 for further detailson parking.

January 1997 Page 213

enm~ozI\)

~:IIJ:15J:

~-<cmen15zs::J>ZC:J>r-

•

~ry<:l

-p ....~-----~ ......_ 6' "'-,'-"' ' ,~~' _---1---_ ~

•

~~

RADIUS Rm

<::>,,<::>'V'\~~>$>

..

q,<::> n'\ <0<::> ~~ '/)<::>>;.V" 'V ~

rll~~ RAt.' "OFF~" '"/ ~ SSD

\/~ -''',-,

~0 The values shown are maxima and applyN where SSD» curve length. Land for~ visibility should be checked from the plans.

~ 1\0

\0~

t \0OJ

"8

1\ "'" ~.><0I'-

~ "--~ 1\ ~ " ~

~ --------0\ ~on

"- "- "'-- -------Standard

'" "- '--- ----- 3.0 Verge

"- --....I'-- -------- - -

5

o

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~

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~

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ifen0" 20-0-0 CENTRALs·co OFFSETencO' Xm:;;,- 15~

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., • •~:c:I:i5:I:

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6000

5760

5000

4080

4000

28802040

2000 3000

RADIUS Rm

1440

1000

360510 720 1020

o

~~~ ~"" ~~ '",

~~,u---=- --~--~-

~ 0-,':> '\':> '1>'" ",':>

#' "---j----- "~ I-- 7,07I \ / -,,'" CENTRA-t:...... ...

\ # ' ,\ \ \ ,,/ ~D .Ot-t-S'b..l....Xm '...... ...~

\ \ \

"".\ \

\ \ I \ C1;..;-\ \ <!'\ I \ \ 1'..,\ I \\ \

\ I \\ \ The values shown are maxima and apply

\ \ where FOSO > curve length. Land forvisibility should be checked from the plans. r- 5.0I- I \ \ ,

I \ \\ ,

\ \ \ ,\ , '\

\ \ \ , '\ ,\ \ \ "

'\Max L"-,- "- R

3.53

1\I~I~I~~For overtaking section

2.5j-

I~I~I~I~~1.76

I Stan ard ............ ----l 3.om Verge1.25

I I I I

5

25

20

30

10

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Xm

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•

•

•


SECTION 3 HORIZONTAL ALIGNMENT

3.1 GENERAL

SECTION 3

provide adequate superelevationcrossover between the curves.

The most important consideration in determiningthe horizontal alignment of a road is theprovision of safe and continuous operation at auniform design speed for substantiai lengths ofroad way. The major aspects influencing thehorizontal alignment are; safety, design speed,topography, costs, vertical alignment and roadclassification.

d) Broken-back curves consist of twocurves in the same direction connectedwith a short straight and should not beused. This type of curve is unexpectedby drivers and is not pleasing inappearance. An attempt should bemade to adopt one simple curve oreven a compound curve.

•

All of these factors must be balanced to producean alignment that is safe, economical, and inkeeping with the natural contour of the land andthe adjacent land use. Poor design will result inlower speeds and a reduction in the capacity ofthe road and safety.

The design of a road on straight alignmentrequires consideration of grades, sight distance,pavement, reservation cross section, etc. Whenhorizontal curves are introduced, additionalitems including radii, transition lengths,pavement widening and superelevation requirespecial attention.

In addition to the specific guidance given in thissection, there are a number of generalconsiderations which are important in producinga safe and economic design. These practices,as outlined below, are particularly applicable tohigh speed situations.

a) Flatter curves for a certain design speedshould be used where possible,retaining the most conservativestandards as possible for the mostcritical conditions.

e) Horizontal alignment and its associateddesign speed should be consistent withother design features and topography.Co-ordination with vertical alignment isdiscussed in Section 4.5.

f) On duai roads, consideration may begiven to independent horizontal andvertical alignments for eachcarriageway.

3.2 MINIMUM CURVATURE

The minimum curvature without the need foradverse camber, superelevation or transitionsis shown in Table 3.1 below.

Design Minimum RadiusSpeed without Adverse(kph) Camber,

Superelevation orTransitions

(m)

140 3800120 2880100 204080 130070 1020·80 72050 510

b)

c)

Compound curves consist of two ormore consecutive curve alignments.They should be used with caution andshould be avoided where conditionspermit the use of a simple curve.Where compound curves are used, theradius of the flatter curve should not bemore than 50 percent greater than theradius of the sharper curve for rural andurban conditions. On this basis, aseveral step compound curve may beused as a form of transition to sharpcurves or a spiral, transitioning from oneradius to the next. This condition canbe relaxed for lower speeds at junctionsand roundabouts.

Reverse curves on high speed roadsshould include an intervening tangent ortransition section of sufficient length to

Table 3.1 Minimum Radii without transitions

Where the radius of curvature is less than thevalue indicated in Table 3.1, trp.nsition curvesshould be used.

3.3 TRANSITION CURVES

The adopted form of transition between astraight and a horizontal curve is a clothoid,also known as transition curve. It provides ausefui and logical section of the alignment forthe development of superelevation and is themost common method adopted.

Where it is not possible to adhere to the valuesof curvature given in Table 3.1, a transitioncurve should be used.


QATAR HIGHWAY DESIGN MANUAL SECTION 3

•

•Minimum Radii with Camberand Superelevation

3.4 CAMBER AND SUPERELEVATION

S = Superelevation (%)V= Design Speed (kph)R = Radius of Curve (m)

On sections of road with radii greater than thatshown in Table 3.1 for the given design speed,the crossfall or camber should be 2% from thecentre of single carriageways, or from thecentral median of dual carriageways to theouter channels. At junctions other thanroundabouts, the cross-section of the majorroad shall be retained across the junction, andthe side road graded into the channel line of themajor road. On horizontal curves, adversecamber shall be replaced by favourablecrossfall of 2% when the radius for the givendesign speed is less than that shown in Table3.1. However, it may be necessary to eliminateadverse camber on larger radii for aesthetic ordrainage reasons. Provision of camber andsuperelevation In low speed areas such ascommercial or residential areas has a tendencyto encourage drivers to drive faster and shouldbe avoided. Refer to Clause 3.8 for specialconsiderations relating to low speed areas.

S = II' /2.828R

The following superelevation and minimumcurves are recommended (Table 3.3).

Table 3.3

On radii less than those shown in Table 3.1superelevation shall be provided, such that:

Where:

7% may be only used at speCial locattons and must have thepermission of the Director 01 Civil Engineering Department prior toits use.

Desig Minimum Radius (m) forn

Speed (a) (b) (c) Superelevallon(kph) Normal Adverse

Camber Camber3.5% 5% 7"10·Eliminated

140 3800 2880 2040 1300 1020120 2880 2040 1300 1020 720100 2040 1300 1020 720 51080 1300 1020 720 510 36070 1020 720 510 360 25560 720 510 360 255 18050 510 360 255 180 127

length of transition (m)design speed (kph)rate of increase ofcentripetal acceleration(m/sec3 )

radius of curve (m)

L=V=q=

R=

L = va / (46. 7qR)

Refer Table 3.3 for restrrcted use of superelevatlon

Where:

The elements for circular and transition curvesare shown in Figure 3.1 and Figure 3.2.

Normally, q should not exceed 0.3 m/sec3 •

However, in particularly onerous cases, it maybe necessary to increase the value up to 0.6misec'. On bends the length of transition shouldnormally be limited to .f(24R) metres. For quickreference some common transition lengths aregiven in Table 3.2.

The length of transition depends on the radius ofthe circular curve and the design speed. Thebasic length of the transition is given by theformula:

Superelevation or elimination of adverse cambershall generally be applied on or within the lengthof the transition curve from the arc end. Thebasic transition appropriate to the design speedhowever will often result in insufficient transitionlength to accommodate superelevation turnover,and it will therefore be necessary to providelonger transitions to match the superelevationdesign.

Transitions are not necessary in urban lowspeed areas such as junctions and serviceroads.

Table 3.2 Basic Transition Lengths (m)

Radius Design Speed (kph)(m)

140 120 100 80 70 60 50

2400 82 512200 89 562000 98 62 361800 109 69 401600 122 77 451400 140 88 511200 163· 103 59 301000 196" 123" 71 37 24800 154" 89 46 31600 119 61 41 26400 91 61 39 22200 122 77 45.


•

•


Superelevation shall not exceed 5%. Only Inspecial circumstances and with prior permissionfrom the Director of Civil EngineeringDepartment will superelevation greater than 5%be considered. Table 3.4 gives examples ofsuperelevation for selected design speeds andradii.

Radius Design Speed (kph)(m)

140 120 100 80 70 60 50

2400 2.88 3.152200 3.15 2.312000 3.47 2.561800 3.85 2.831600 4.33 3.18 2.211400 4.95 3.64 2.531200 5.78' 4.24 2.951000 6.93· 5.09' 3.54 2.26800 6.36' 4.42 2.83 2.17600 5.89' 3.77 2.89 2.12400 5.66' 4.33 3.18 2.21200 6.6S· 4.42

Special Circumstances see above

Table 3.4 Superelevation of curves (%)

Progressive superelevation or removal ofadverse camber shall be achieved over or withinthe length of the transition curve from the arcend. On existing roads without transitions,between Y2 and % of the cant shall beintroduced on the approach straight and theremainder at the beginning of the curve.

SECTION 3

When expanded, this formula provides theequation for the vertical reverse curve to beused for the superelevation curve. This reversecurve is shown in Figure 3.3

In some difficult areas, even the aboverequirements can lead to drainage problems,ego where the superelevation is applied againstthe longitudinal gradient. It may be necessaryto either modify the horizontal alignment tomove the superelevation area, increase thevariation in grade of the edge profile, or appiy arolling crown. Areas susceptible to suchdrainage problems shouid be identified at anearly stage in the design process, before thehorizontal alignment is fixed.

Ix I

I ~:r__! ~[~I --=L _

Y = 3SX;/L 2 _2SX'/L 3

wh ere Y = offsetS = maximum offset

X =distance from start of application

L = length of application

Figure 3.4 shows typical methods of developingsuperelevation by rotating about the edges andthe centre of the road. The designer should usethe most appropriate method to suit thesituation. For dual carriageways, greaterconsideration of topography, cut and fill,catchment and median drainage is required.

Superelevation shall not be introduced, noradverse camber removed, so gradually as tocreate large, almost flat areas of carriageway, tocause driver discomfort or to kink the edges ofthe carriageway. A satisfactory appearance canusually be achieved by ensuring that thecarriageway edge profile does not vary in gradeby more than about 0.5% from the line aboutwhich the carriageway is pivoted, and by amplesmoothing of all changes in edge profile. It isrecommended to ensure that a minimumlongitudinal gradient of at least 0.5% ismaintained wherever superelevation is to beapplied or reversed. The distance to satisfy thisconstraint is given by the equation:

G=%xSIL

Where:

G = rate of change of gradient(0.5%)

S = change in channelsuperelevation relative to theline about which thecarriageway is pivoted (m)

L = length required toaccommodate the change insuperelevation (m)

Figure 3.3 Reverse Curve Formula


QATAR HiGHWAY DESiGN MANUAL

BCC

Circular Curve-

Figure 3.1 Circular Curve Elements

ECC

SECTION 3

Elements:PI ::;: Point of Tangent IntersectionBCe::;: Beginning of Circular CurveECC::;: End of Circular Curve/).C = Deflection Angle of Circular CurveR ::;: Radius of Circular CurveT ::;: TangentLC ::;: Length of Curve

,.

..

Symmetrical Form of Transition to Circular Curve

Figure 3.2 Transition and Circular Curve Elements

January 1997

Elements:

PI = Point of Tangent IntersectionBTC = Boginning of Transition CurveBee = Beginning of Circular CurveECC = End of Circular CurveETC = End of Transition Curve6. = Total Deflection Angle6r = DeJlection Angle: of Transition Curvefie = Deflection Angle of Circular CurveR = Radius of Circular CurveMT = Main TangentTK ::;: Short Tangent of Transition CurveT L = Long Tangent of Transition CurveX M = Abscissa of the Center of Radius PointLi R = Circular Curve OffsetX = Abscissa of BCC or ECGY = Ordinate of BCe or ECG

LT = Length of Transition CurveL C = Length of Circu lar C urva

Page 3/4

•


- -/- - - - l,!!id~eqge.2J t!!v·~ed way

O..!!ts~e ~g~ofJ.ra~elJedwayo~

-::';

"-~;;;a.

-~

ct Grade

o0000enw

-~

Suoerelevation runoff

Runoff slope~~

o

Runouto....W

Tanaen!

Slope 1:400~ ~

Normal \ _.- -crown - I- - - f- -I-- _

•

A B c ~D ct. Profile control

Travelled way revolved about centreline

Tangent

~0000enW

Runoff slope~ ~~...'!ts~e ~dg~oUra.'!.elled way

- -~Ci.. Grade ~

•Runout

o....woo....en

Slope 1:400 \

Normalcrown - _.--

_ c- -

r - -

Superetevation runoff

ormal CLProfile grad~ _-------- ------

Inside edge of travelled way

A B cInside edaeProfile control

Travelled way revolved about inside edge

I Tangent IRunouto

0 ........ wen ~

Normalcrown -:-.. __

Superelevation runoff

Normal ct...Qrofile grade

It Grade

~Io00enw

Outside edge of travelled way--§-~

'ni>~

RunOffSlope~- - -

"-~

a.- - -~~ - - - -Inside edge of travelled way

A B c D Outside edge......... Profile control

Travelled way revolved about outside edge

Notes:

A = Norm al crownB = Level high side norm al crown low sideC = Superelevation at normal crown rateo = Full superelevation

Figure 3.4 Development of Supereievation



The rear wheels of vehicles do not follow thefront wheels exactly on horizontal curves, and itis more difficult to steer the vehicle on curves.For these reasons it is recommended toIncrease travelled way widths on curves.

3.5 WIDENING ON CURVES

SECTION 3

..Widening is required for carriageways of lessthan standard width and for low radius curves ofstandard width to allow for the swept path oflong vehicles.

For carriageways of standard width, (3.65m,7.3m and 11.0m for 1, 2 and 3 lanesrespectively) an increase of O.3m shall beallowed when the radius is between 90m and150m. Two lane roads of width greater than7.9m require no additional widening. Wideningof road widths when the radii is less than 90m iscovered in Section 6 Junction Design.

For carriageways less than the standard width,widening shall be as shown in Table 3.5.

LaneWldlh Radius AdditionalWidlh(m)

Standard Radius less than gOm refer to -Width SeeUon 6

Standard Radius between gDm and 0.3Width 150m

Standard Radius grealer than 150m NoneWidth

Less than Radius less than gOm refer toStandard Section 6Width

Less than Radius between gOm and 0.6Standard 150m subject to maximumWidth carriageway widths o17.9m

and 11.9m (for 2 and 3 lanesrespectively)

Less than Radius between 150m and 0.5Standard 300m subject to maximumWidth carriageway widths of 7.3m


Lesslhan Radius between 300m and 0.3Standard 400m sUbject to maximumWidth carriageway widths of 7.3m


Table 3.5 Application of Additional LaneWidth


•

,.QATAR HIGHWAY DESIGN MANUAL SECTION 3

Circular curve

_--'t--_- -/' -- --:;:;~~~~~;--....".. ./ axirnuOl s.upe~elevation "S"

& widening "w"

..Widening

./--Avoid reserve curveat this point

Transition curve may be widened on inside and outside

\II-ct-_

\

Simple curve may be widened on inside only

Figure 3.5 Widening of Pavement on Curves



viewpoint is at the same distance from the startof the curve then an improvement is notachieved, in fact the kink will appear to berather more pronounced.

Even with a large radius curve, it is not possibleto avoid the illusion of a sharp change indirection if the approach straights aresufficiently long, refer Figure 3.8. The bestresults are likely to be achieved with the flowingalignment when straights can be dispensedwith. This of course is not always possible or infact desirable. For example, in roads Which arenot dual carriageways, the sight lines onstretches of road where overtaking is permittedmust be based on passing sight distance andnot stopping sight distance. Straight lengthsmay then be required to achieve these sightdistances. Also, it should be borne in mind thatsuch effects will not necessarily be significant inthe total view for any particular case. Eachdesign should be considered in its landscapecontext. This is true of many aspects of internalharmony, although the greater the designspeed, the iess the externai features modify theinternal views. This occurs because vegetationand buildings are further back from the roadedge, the carriageways are wider, sight lineslonger and the roadworks generally constructedto a larger scale.

3.6 HARMONISING THE ALIGNMENT

The choice and arrangement of the linearelements are crucial factors in ensuring that theroad will look right in its surroundings and willbe pleasing to the driver of the vehicle. Thedesign shal[ also provide a safe route, with thenecessary stopping sight distances.

The aim of flowing alignment is to combine thevarious components in a manner which resultsin the road being experienced by the road useras a free-flowing, harmonious form withoutvisual discontinuities. Such a design results inbetter integration of the road into the landscapeand helps to make the road a constructionwhich is visually pleasing from the viewpointboth of its users and those outside the roadreservation.

The principles of flowing alignment are closelylinked with the way in which the driver sees theroad line and in particular the shape of the roadedges.

It is advisable to avoid small changes indirection in a flowing alignment. These arelikely to appear unsatisfactory from the vehicle.Furthermore, small transverse displacementscan present a confusing prospect for the driver.

StraIght

Shortcurve

Straight

I

Figure 3.6 Example of Kink

./

Figure 3.7

... ..._-- , ,,8

Un

Improved View with LargerRadius

•

•

•In all cases, when additional width is required,the extra width should be applied uniformlyalong the transition curve. Where existingalignments are to be improved the Wideningshould take place on the inside of curves. Thisis shown in Figure 3.5.

When two straights are connected, the use of ashort horizontal curve Is likely to cause theappearance of a kink, refer Figure 3.6. In suchcases the impression can be improved byemploying a larger radius, but an improvementonly results provided the views being comparedare taken from the same distance from thevertex of the curve, refer Figure 3.7. If the

January 1997

Abrupt changes in direction can beunsatisfactory on access roads as well ashighways. In Figure 3.9 the straights have beenjoined without the use of a horizontal curve.The appearance is quite different when ahorizontal curve is added, refer Figure 3.10.

Page 3/8

•QATAR HIGHWAY DESIGN MANUAL SECTION 3

Figure 3.8 Illusion of a Sharp Bend with Long Straights

Figure 3.9 Anguiar Geometry

January 1997

Figure 3.10 Curved Geometry

Page 3/9


Short straight sections of road should not beinterposed between horizontal curves ofopposite sense since the appearance of a kinkis likely to result, refer Figure 3.11. A possiblesolution is the use of a pair of transition curvesrefer Figure 3.12. When designing for slowerspeeds or in the case of very large radii it maybe feasible to join the two curves directly asshown in Figure 3.13. This could be done withcare since here also an impression of lack offlow may result. '

SECTION 3

Similarly, in the case of two subsequent curvesin the same direction. the use of an intermediateshort straight, as shown in Figure 3.14. is likelyto produce an unsatisfactory visual effect. Herethere may be the possibility of replacing the twocurves and the straight with one circular curve,refer Figure 3.15. Another possibiiity may be tointerpose one transition curve between the tworadii. refer Figure 3.16.

A series of reverse curves is likely to produce aflowing alignment which is pleasing to the eyeand comfortable for the driver. This type of lineis ideal for integrating a route into an undulatinglandscape.

•

Figure 3.11 Short Straight Between Curves

Circularcurve

Straight

Circularcurve

Figure 3.17 summarises alignments to beavoided and those to be attained wherepossible.

3.7 HORIZONTAL CLEARANCES

Generally. no structures apart from roadsidefurniture. such as signs and lighting coiumns,are allowed to fall within the road reservations.The positioning of signs and other streetfurniture should be in accordance with the QatarTraffic Manual. If it is not possible to positionstructures outside the reservation, considerationshould be given to providing a safety barrier orsafety cushions, refer clauses 5.15 and 5.16respectively. Setback of crash barriers is dealtwith in the clause referenced previously.

Structures should not be placed within 1.2m ofthe edge of the hard shoulder, or a.6m of akerbed road.

•

Circular Circularcurve curve

Transition Transition

Figure 3.12 Back to Back Transitions

I~

Circular Circularcurve curve

Figure 3.13 Back to Back Circular Curves

January 1997

It is important to ensure that sight distance isnot impaired. especially at junction anddriveway locations. Refer to Section 2 SightDistance.

Page 3/10


Circularcurve Straight Circular

curve

SECTION 3

Figure 3.14 Two Subsequent Curves in the Same Direction

Circular curve

Circularcurve

Transitioncurve

Circularcurve

Figure 3.15 Single Circuiar Curve Figure 3.16 Single Transition CurveBetween Two Curves

•

To be avoided

X 1 Small change of direction- -~ X 2 Short horizontal curve between two straights

~ X 3 Short straights between horizontal curves ofopposite sense

~ X 4 Short straight between horizontal curves ofthe same sense

~ X 5 Out of balance alignment

To be attained

~ V 1 Well-balanced alignment

~ V 2 Use of curves rather than straights wherefeasible

Figure 3.17 Summary of Alignments to be avoided and those to be attained




• Street patterns should minimiseexcessive vehicle travel.

• Local streets should be designed tominimise through traffic movements.

• The local circulation should not have torely on extensive traffJc regulations orsigns in order to function properly.

Minimum recommended centre line radiusfor local roads (TR3) is 80m and foraccess roads (TR4) is 40m

Minimum recommended centre line radiusfor local roads (TR3) is 130m and foraccess roads (TR4) is 5Sm

Table 3.6 identifies three possible road sectionsat bends.

Case 3 4% crossfall applied across the fUllsection, falling from the outer kerbtowards the inner kerb

Case 2 Normal 2% crossfall applied across thefull section, falling from the outer kerbtowards the inner kerb

Minimum recommended centre line radiusfor local roads (TR3) is 100m and foraccess roads (TR4) is 45m

The introduction of cUlVes to residential roads isan effective form of speed control. Howeverbends of smaller radius than those given inTable 3.6 exaggerate this effect and withparticularly sev.ere bends, induce the sharpbraking/acceleration behaviour which has beenidentified as undesirable.

Case 1 Standard cross section, carriageway fallsfrom centre-line at nominal 2%. Tocontinue this cross-section around acurve would introduce adverse camber.

Table 3.6 Possible Road Sections atBends

Traffic generators within residentialareas such as schools, mosques orshopping facilities should beconsidered in the overali design.

Local streets should be designed todiscourage excessive speeds.

The local street system should bedesigned for a relatively uniform lowvolume of traffic.

•

•

•

Residential roads selVe or give access toprivate dwellings or properties. They should bedesigned to selVe the needs of the residentsand at the same time discourage through trafficby ensuring that the roads are not used as ashort cut.

Generaliy the design of roads in residentialareas and local street systems should considerhe foliowing:

•

•

Pedestrian - vehicular conflict shouldbe minimised.

Parking requirements should beprovided without reducing visibilityrequirements or the safe operation ofthe road.

In short cul-de-sac or loops, such as 60m orless in length, where speeds are low thedesirable minimum inner kerb radius is 15mwith an absolute minimum of 10m.

The minimum radii to be provided at junctions isdiscussed in Section 6 Junction Design. •

• There should be a minimum ofintersections.

• Local streets should be related totopography from the standpoint ofdrainage, economics and amenities.

The speeds on residential roads areconsiderably lower than major, secondary andprimary roads. As the dynamic element is notso critical, it is not normal to implementtransitions as part of the horizontal alignment,nor to apply superelevation to a cUlVe.

The typical driveway should be designed forpassenger-car operation only. For a 90 degreeturn, an inside radius of 5m and an outsideswept path of a 9m radius will comfortablyaccommodate most drivers In all passengercars. Temporary encroachment on the wrongside of a residential street while entering aprivate driveway is generally consideredallowable. For higher traffic volumes expectedat the driveways of school or apartment carparks, increased driveway widths arerecommended.

The visibility requirements for bends onresidential roads Is detaIled in Section 2.


SECTION 4

4.2 MAXIMUM AND MINIMUM GRADES

For aesthetic reasons the length of verticalcurves should be substantially longer than thelength required for stopping sight distance.

Generally gradients should be fixed to beconsistent with the topography through which thehighway passes in order to minimise excessiveunnecessary earthworks. The maximumgradients for design purposes shall be as shownin Table 4.1.

Maximum Gradients

Route Classification Max. Grade(%)

Primary Route 4Secondary Route 6Tertiary Routes

Local/District Distributor 6Major/Minor Access 10Cui de Sac 10

Table 4.1

surface, the profile shall be established so thatthe low edge of the finished shoulder is at least0.5m above the temporary water level. If thewater table is permanent then the road formationlevel should be at least 1.0m above the tabledue to the possibility of capillary action. In areasof rock, if practical, the profile should beestablished so that the low edge of the finishedshoulder is at least 0.3m above the rock level.This should avoid unnecessary rock excavation.

A "roller coaster" or "hidden dip" type of profileshould be avoided. A smoothly rolling profile,rather than a straight profile can often result ineconomy of construction, without sacrificingoperating characteristics and aesthetics.

A smooth prbfiie with gradual changes,consistent with the class of highway and thecharacter of the terrain, is preferable to avertical alignment with numerous sharp breaksand short lengths of gradient.

4.1 GENERAL CONTROLS

SECTION 4 VERTICAL ALIGNMENT


As the driver progresses along the profile withincreasing chainage, an increasing gradient isdenoted as being positive (+ve) and adecreasing gradient is denoted as beingnegative (-ve).

A broken-back profile (two vertical curves in thesame direction separated by a short section oftangent grade) is not desirable, particularly insags where a full view of the profile is possibie.

Vertical alignment consists of a series ofgradients connected by vertical curves. It iscontrolled by safety, topography, highway class,design speed, horizontai alignment,construction costs, adjacent deveiopment,drainage, vehicular characteristics andaesthetics. The verticai alignment is usuallyreferred to as the profiie.

..

Where an at-grade intersection occurs on ahighway with moderate to steep grades, thegradient through the intersection shall bereduced if possible. This is beneficial forvehicles making turns and stops, and serves toreduce potential hazards.

In residential areas, where properties lieadjacent to the road, the desirable maximumgradient is 3.3%. Gradients approaching "Stop"or "Give Way" junctions should be a maximum of+/- 2% for a minimum of 15m before the "Stop"or "Give Way" line. Refer Figure 4.1.

A superelevation runoff occurring on a verticalcurve requires special attention in order toensure that the required minimum verticalcurvature is maintained across the pavement.For example, the lane profiie on the oppositeside of the road from the superelevation controlline may have sharper curvature due to thechange in superelevation rate required by thesuperelevation runoff. It is therefore necessaryto check both edges profiles and adjust wherenecessary in order to maintain the desiredminimum vertical curvature.

MaJor Road

Figure 4.1

Minor Road

15m min

Vertical Alignment at T-JunctionApproach

In flat terrain, the elevation of the profile is oftencontrolled by drainage. The vertical profile mustbe positioned such that adequate drainagestructures can be constructed. In areas wherethe surface water is above the ground level orthe groundwater table is immediately below the

For drainage purposes, a desirable minimumlongitudinal gradient of 0.5% on kerbed roadsshall normally be adopted. The absoluteminimum longitudinal gradient for kerbed roadsshall be 0.3%. In flat areas careful considerationshould be given to drainage requirements.



For single carriageways where the horizontalalignment has been designed to allowovertaking, full overtaking sight distance shouldnot be obstructed by crests. Conversely there isno merit in providing an overtaking crest if thehorizontal curve does not permit overtaking.K-values for vertical curvature on singlecarriageways are given in Table 4.3

There are two prime factors that affect thechoice of crest curvature, visibility and comfort.At design speeds of 50 kph and above, a crest inthe road will restrict forward visibility to theminimum stopping sight distance beforeminimum comfort criteria are approached, andconsequently desirable minimum crest curvesare based upon visibility criteria.. This isdiscussed further in Section 2 Sight Distance.

Design Minimum Avoid AbsoluteSpeed K-value for Crest Minimum(kph) an K-values K·value

Overtaking in thisCrest Range Crest Sag

100 400 400 -100 55 2680 285 285 - 55 30 2070 200 200 - 30 17 2060 142 142 - 17 10 1350 100 100 -10 6.5 9

The use of over edge drainage may also beconsidered in conjunction with surface channelsor ditches in rural areas. Refer to Section 8 forfurther details on drainage.

4.3 VERTICAL CURVES

Vertical curves shall be provided at all changesin gradient, except at junctions and on lowerclasses of roads where the arithmetic change isless than 0.5%. The curvature shall be largeenough to provide for comfort and whereappropriate, stopping sight distances for safestopping at the design speed. The use of thepermitted vertical curve parameters will normallymeet the requirements of visibility. However,stopping sight distance should always bechecked because the horizontal alignment of theroad, presence of crossfall, superelevation orverge treatment and features such as signs andstructures adjacent to the carriageway, will affectthe interaction between vertical curvature andvisibility.

A vertical curve is a curve on the longitudinaiprofile of a road which allows for a change ofgradient.

A crest (summit) curve is a vertical curve whichis convex in shape. Generally the sign of thegradient as the driver travels up chainage,changes from +ve to zero to -ve.

Table 4.3 K-values forCarriageways

Single

A sag (valley) curve is a vertical curve which isconcave in shape. Generally the sign of thegradient as the driver travels up chainage,changes from -ve to zero to +ve.

A K-vaiue is a constant related to the comfort ofthe driver.

Vertical curve lengths can be determined bymultiplying the K-values given by the algebraicchange of gradient expressed as percentage, ie+3% grade to -2% grade indicates a gradechange of 5%.

For dual carriageways curvature shall be derivedfrom the appropriate K-value in Table 4.2.

Design Desirable Absolute MinimumSpeed Minimum K-value(kph) K-value for

Crest Crest Sag

140 230 182 50120 182 100 37100 100 55 2680 55 30 2270 30 17 2060 17 10 1350 10 6.5 9

Table 4.2 K-values for Dual Carriageways

Particular attention is needed on dualcarriageways to check any restriction to visibilitycaused by safety fences, median kerbs, bridgepiers, etc. especially at combined horizontal andvertical curvature.

Visibility at sag curves is usually not obstructedunless overbridges, signs or other features arepresent. Forthese curves, comfort criteria appiy.The maximum rate of vertical acceleration is tobe taken as 0.3m/sec2• However for designspeeds of 70 kph and beiow, in unlit areas,flatter sag curves are necessary to ensure thatheadiamps illuminate the road surface for atleast the required stopping sight distance. Sagcurves shouid normally be designed not lessthan the absolute minimum K-values in Table4.3.

Where, at crests, the sight line is across theverge, consideration shall be given to the designof a lower verge profile in order to allow for amaximum overall height of landscaping of 0.5m

More generous sag curves may be requiredunder bridges and through underpasses etc. inorder to maintain the envelope of required sightdistances.

•



Figure 4.5

Figure 4.4

IU~,

Valley curve Level Valley curve

• •Straight

I I

••

Tangents, especially short ones, between twovalley curves can result in an awkward lookingline, refer Figures 4.4 and 4.5.

radius must be sufficiently large for theappearance of a kink to be avoided, referFigures 4.2 and 4.3. Even large radii will givethe appearance of an abrupt change in directionif the viewpoint is sufficiently far from the curve,but this is unimportant since, at great distances,it will not be found disturbing. Drivers do not tendto become aware of an approaching valley curveuntil they are about 500m from the start.

The choice of vertical profile is fixed mainiy bythe geometric standards but is also influenced bythe nature of material in the cuttings and the totalearthworks. Ideally a balance should beachieved between cut and fill, and thecalculations should include compaction factorsfor shrink and swell and allowance for suitableand unsuitable material.

This section should be read in conjunction withClause 3.6, harmonising the horizontal alignmentand Clause 4.5, combining the horizontal andvertical alignment.

Due to the topography of Qatar, it is unlikely thatsteep gradients would be implemented whichwould require a climbing lane. However, if ascheme including a climbing lane was to beconsidered, reference should be made to the UKDepartment of Transport pUblication, DesignManual for Roads and Bridges, Volume 6,Section 1, Highway Link Design (TD 9/93).

4.4 HARMONISING THE VERTICALALIGNMENT

The valley curve plays an important part inachieving internal harmony in the alignment,especially since it can often be viewed along itswhole length at one time. This is not normallypossible in the case of .crest curves but for thisreason particular attention must be paid toensuring that visual continuity is maintained.This leads to the avoidance of short summitcurves even though they may satisfy visibilityrequirements.

•

•

_ _ G=,a.=.di.=.on""---II I Gradient-1--1- ..Valleycurve

Figure 4.2

Figure 4.3

As is the case with horizontal curves andstraights, when a valley curve is used to join twogradients, or a gradient and a level length, the

A vertical curve is seen as a hyperbola.Whether or not the junction of a tangent and avertical curve presents the appearance of a kinkdepends on the curvature of the sharpest bendof the hyperbola and its location in relation to theend of the tangent. It is desirable that thehyperbola does not start at the position of itssmallest radius. In critical cases it is advisableto examine perspective draWings of the line. Anindication of the effect of small and large radiusvertical curves on the drivers view are shown inFigures 4.6 and 4.7 respectively.

I,/

{}I)

Figure 4.6


•I Summitcurve

Valleycurve

Summit Icurve

-SECTION 4QATAR HIGHWAY DESIGN MANUAL

•\IIIII

Q~

tJ/1

Figure 4.7 Figure 4.10

•b,mm,lr~urv~11,

Valleycurvo

I ,mmJF~urv~'l

-

When a terrace is created by a sequence ofsummit and valley curves, whether or not thereare tangents between the curves, it is likely toresult in an unsatisfactory view if two summitscan be seen at the same time. An example isshown in Figure 4.12.

r •• •I I I I

/lwl\v/N/XV)Nlk'iiNhVJ:I0\\Vi\w:w:t\VXWI

A level length of road containing a short lowsummit curve can cause a visual discontinuitysince the distant length of road, diminished insize by perspective, can be seen over the crest,refer Figure 4.8.

Figure 4.11

1\~/

"Figure 4.8

Similarly the use of a reverse curve in thelongitudinal section, causing a small change inlevel, can result in a visual discontinuity due tothe road surface disappearing from view andthen reappearing. An example of the effectwhen a reverse vertical curve is used inconjunction with level straight lengths is shown inFigure 4.9. A view of this type can occur with adouble reverse curve, refer Figure 4.10. In thecase illustrated, the line can be improved byincreasing the length of the valley curve anddecreasing those of the summit curves, referFigure 4.11 .

-ivm:;; MINlm;1 (PIi \vA \Vimx \\l\\\h\\91\\h\\95:

Figure 4.9

~~

"""""'" II Valley Summit Valley Summit

curve curve curve curve

~~

\~7 I

~ ,,//, ,

,

Figure 4.12

The lower the terrace is placed and the shorterits length the more disturbing it is likely toappear, since it can be viewed from a shorterdistance. All terraces tend to appearunsatisfactory when seen from the top. As withthe horizontal alignment, the ideal solution forthe verticai alignment is a series of wellmodulated vertical curves proportioned so thatthey avoid the problems discussed. Such asolution can, of course, oniy be used when theland form and other controlling factors make itpossible.



4.5 PHASING OF HORIZONTAL ANDVERTICAL ALIGNMENT

Table 4.4 summarises the type of verticalalignment to be avoided and that to be attained.

Longitudinal section

Horllontal

--=:1:R~.

If the out of phase lengths are small this is notlikely to be significant. In fact it is probablyadvantageous to have overlap. This may beconsidered to contribute to the integration of thetwo aspects of the line. When an overlap isused it should normally be small in comparisonwith the length of the element. Yet there areexceptions to this: the plan and profilecombination of the type shown in Figure 4.14 willprobably produce awkward looking perspectives.In this arrangement, the horizontal curve ends atthe same point as the vertical curve begins.

SECTION 4

Figure 4.13

Plan

V:llleyLevol curvo Gradlenl

Figure 4.14

If prevailing conditions prevent using longer,coincident curves, it is possible to achievesignificant improvement if longer overlappingcurves are implemented as shown in Figure4.15.

Summary of desirable/undesirable combinations ofvertical alignment

c::::::::::TI:: XShort summit curvesbetween gradients

~ X Short valley curvesbetween gradients

Short tangent betweenC::I I I I-----=' X summit curves

D I -c1 X Short tangent betweenI valley curves

Reverse vertical curve

I 1 :r I I X causing small change inlevel, on a level lengthor gradient

XA level length or gradient

CD ITI containing a low valleycurve

A level length or gradient

I I I I I I X containing a low summitcurve

[[I]Terracing on which two

I I I X summits can be seen atone time

c:r=D::::::J ../ Well balanced alignm.ent

~Use of curves rather than

../ straights or gradientswhere feasible

Table 4.4

To obtain a satisfactory alignment it is importantto integrate the vertical and horizontal aspects ofthe line. In order to accomplish this, the engineershould consider the road as a three-dimensionalunit. The elements of the horizontal and verticalalignment should be In phase wherever possible.In other words, the corresponding elements inthe horizontal and vertical planes should start atapproximately the same points and end atapproXimately the same points, refer Figure 4.13.

•

j&\ffffI'

•



Horizontal

s,,,rnh

' I '""" ~." .. .. .~

~

SECTION 4

,.

Figure 4.15

ValloyLovol curve Gradiont

The best results would be obtained if coordinated curves of ionger radius could be used,refer Figure 4.16. The following combinations ofhorizontal and vertical alignment are someadditional examples of those which are likely toresult in an awkward appearance. A summary ofdesirable/undesirable combinations of alignmentis shown in Table 4.5.

Figure 4.16

•

Table 4.5 Summary of desirable/undesirable combinations of alignment

Figure Notes

4.17 • A short valley curve within aHorizontal curve horizontal curve. This is similar to the

~ case of a short valley curve occUrring

I I I Ialong a straight, but the impression ofdiscontinuity will probably be even

Y/t,<.()"'VA'0mt..Y;A\(jI.\~t\WAYlt,.v. more pronounced.

11!~umm,11 V3UOy·-lsummlllLev "I curve curve CUIVII Love]

I I I I

I2-~-~8



•

•

4.18 I • Horizontal curvc • Low summit curve within a horizontal

~curve. Here too the discontinuous

I I I Iappearance is liable to be even morepronounced than with the low summit

VJXwlR/)},.'JINJliWJIvtIlVl1;;;;2\YiXWl..YJ/J(,curve on a straight.

l,l~3118~ [summitt valJo~"i,Loval CUrY" curve curve Lovel

---:>---~

4.19 • • Horlzol'lal ~urv• .. • A short vertical curve connecting

cr:c:gradients in a long horizontal curve.This arrangement is liable to result inthe illusion of a pronounced kink in thealignment. Small changes in directionbetween tangents are as undesirable inthe vertical plane as they are in the

I V.II., I horizontal plane.Gradient curvo Gradlllnt

---------:---7v---- il'~~

I"'

4.20 Horizontal • A horizontal curve following a straightStraight , I Curve and starting on a valley curve which, , •

follows a gradient. This combination

~tends to give the horizontal curve theappearance of a sharp bend.

Gradient I Valley Curved d .

4.21 Horizontal • Valley curves joined by a level lengthStraight , cliNg

i • I or gradient and occurring along a

1~'straight followed by a horizontal curve.Valley curves joined by a tangent areundesirable in themselves but when

~ combined with a horizontal curve in thisway they can produce the results

Valley IvaUIIY shown.Gradient curve Levol curve Gradient

I

c:;J<; I

[:~;;;::J

January 1997 Page4n

4.22 Hallzanlal • A summit curve followed by a valleySltalght I tllrv. ISl13fghlcurve occurring along a straight

I I I" followed by a horizontal curve. Adisjointed effect is liable to result when

~the beginning of a vertical curve ishidden from the driver by an

..I ,"mm" TV,I., 1 intervening summit while theGradl.n! ell..... CUNa r:adtDnl

continuation of the curve is visible inI I Ithe distance beyond.

V ~4.23 Horizont.l • A tangent length between a verticalSlra!phl cUlY"I curve and a compound curve.

,.. I' :I~Wherever possible such a tangent a~bshould not be used. Instead the

~vertical alignment should be soarranged that the curves can be joined

vall.~ I I Summit - directly.<lUNa Gradlant tillY"

I

kZ ( s:JI•,a

l

4.24 Horizontal • A short horizontal curve within a long• ....Stralght I • curva r valley curve. This combination can

result in the appearance of a kink.

:IJ::;•

Valley curve ..

~4.25 Hor!l:onlal • A short horizontal curve occurring on

~ a short summit curve. This can be

~dangerous since the driver is unable tosee the continuation of the curvedhorizontal alignment. An even more

~ unsatisfactory case would be if the

. .I I.' , horizontal curve started immediatelySummll over the summit.

Gradient CUrvB GradllH\1

4.26 Horizontal Horlzofllal • A reverse horizontal curve with thecurve I curvechange in curvature situated at the topI

lITof a sharp summit curve. This also isa dangerous arrangement since thedriver is not able to anticipate the

~change in curvature.

/ //(\

Gmdllln,[ Summit curve IGr3dlont


Table 4.5 Summary of desirable/undesirable combinations of alignment

SECTION 4

•

•



The minimum vertical clearances are specifiedto prevent vehicles or their loads from cominginto contact with any structure or roadsidefurniture.

Minimum clearance shall be prOVided to allstructures or roadside furniture that overhangsthe carriageway. These include any bridge orbUilding structure, sign gantry, overhead cablesor suspended lighting.

Where a road passing underneath a bridge ison a sag curve, the headroom given aboveshall be increased In accordance with Table4.7. The sag radius is measured along thecarriageway over a 25m chord.

The minimum clearance over the carriagewayIs 5.5m. This Is to be provided across alltrafficked lanes Including and shoulder or edgestrips. The figure of 5.5m allows for 200mm ofpavement construction which may be appliedduring the maintenance of the road.

of desirable/combinations ofand vertical

Summaryundesirablehorizontalalignment

VERTICAL CLEARANCES

Horizontal and vertical

~curves in phase (the

../visual continuity can oftenbe improved by haVing

t=::r::D the horizontal elementsslightly leading thevertical ones)

~

../Where possible use three-

~dimensionable curves andavoid the use of straights

~

r:==CJ=:1 ../ Use a well balanced threedimensional alignment

Table 4.6

4.6

Where a public utility specifies a minimumvertical clearance to its plant then the greater ofthe clearances must be provided for. Protectivemeasures may be required at overhead cablecrossings such as guardwires. Guidance maybe sought from the Ministry of Electricity andWater when planning works in the vicinity oftheir installations.

Table 4.6 shows a summary of thecombinations of horizontal and verticalalignment to be avoided and that which is to beattained.

------- Horizontal curve

I I I I I X containing a low valleyI curve within its length

------- Horizontal curve

I I X containing a loW summitI I I I curve within its length

------- Short vertical curve

~ X between gradients in ahorizontal curve

Horizontal curve following

"'"Lt::1 Xa straight and startingon a valley curve whichfollows a gradient

Valley curve joined by a-........ level length or gradient

X and occurring along a

t't--,-,-:c1 straight followed by ahorizontal curve

Summit curve followed by

"' Xa valley curve occurring

r:r=t--= along a straight followedby a horizontal curve

--.. A tangent length between

X a vertical curve and a

rcu compound curve

----- X Short horizontal curve

r-:- ::J within a tong valley curve

------ Short horizontal curve

~ X occurring on a shortsummit curve

Reverse horizontal curve------ with the change in

X curvature situated at thee::cr-----, top of a sharp summitcurve

-------------c:e::L:b X Out of phase alignment

~X

Badly balanced

t=r:11f1 arrangement

•



Sag Radius Additional(m) Clearance

(mm)

1000 801200 701500 552000 453000 256000 15

>6000 nil

SECTION 4

• Maximum driveway gradients toproperties shall be 1 in 15.

• Low retaining walls/planters may beused to assist in matching road levelsto existing plot boundaries. However,they shall not be allowed present ahazard to vehicle or pedestrian traffic.

Industrial

Table 4.7 Sag Radius Compensation • Maximum gradients to be 1 in 20 dueto road usage by heavy vehicles.


Special considerations for vertical alignment arerequired in many areas, one of the greatestconcerns to the engineer in Qatar being theflatness of many areas and subsequent surfacewater drainage difficulties. Section 8 details therecommended minimum gradients andcomments on the importance of drainage innearly level areas.

Below are listed a number of vertical alignmentconsiderations specific to certain conditions thatthe engineer should be aware of:

Residential and Commercial

• Need to match threshold levels in areasof existing development

• Preferred maximum siope acrosshousing plots is 1 in 30

• Valley points where water may collectshould be kept away from residentialaccesses

•

•

•

After long or steep down gradients,heavy vehicles may require additionallevel areas for braking distance oremergency run-off lanes.

On long or steep up gradients, heavyvehicles may require climbing lanes toallow faster vehicles to pass.

Change in transverse or longitudinalgrade should not be significant so as tocause loss of load.

•

• Road alignment should preferably bekept below adjacent property level

• Minimum length of vertical CUNe shouldbe 30m due to construction tolerances

• Vertical alignment changes whereabrupt or repetitive (such as in flatareas) can be disguised by being madeat the horizontal bends

• Levels of existing utilities requireconsideration regarding the verticalalignment of new roads

• Footpath maximum longitudinal gradientto be 1 in 10. Steps may be used toovercome worse gradients but are notpreferred as they limit access bywheelchairs



SECTION 5 CROSS SECTIONAL ELEMENTS

5.1 ROAD RESERVATIONS

In general the different road reservations areintended to provide drivers with adequate sightdistances and ailow the public utilities sufficientspace for existing and proposed piant. Wherespace for utilities is limited, "way leaves"outside the road reservation may be obtainedby contacting the relevant pianning authority.

Figures 5.1 to 5.9 show cross sections depictingthe essential elements in typical sections fortwo way single carriageways and dualcarriageways for urban and rural roads. Eachof the different elements comprising the crosssections is discussed in detail in the followingclauses. The cross sections shown are typicaland the final layout of the reservation should beagreed with the Director of the Civil EngineeringDepartment.

The recommended reservation details for ruralroads are similar to those for urban roads butreflect the reduced access and drainagerequirements of the rural situation. Generallyfor the rural situation the near side of thecarriageway would not be kerbed although flushkerbing may be considered at certain locations.Raised kerbing to the median of rural dualcarriageways should only be provided atspecific locations ego bridges, U-turns. In allcases an edge strip shall be provided betweenthe kerb and lane edge. Verges shall bedesigned to fall away from the carriageway inthe rural situation and thus water will drain tosurrounding ground.

Shoulders are not normally required on ruralsingle carriageway roads but, generally, edgestrips would be included in the design. Edgestrips may also be considered as an alternativeto fuil hard shoulder construction on rural andurban dual carriageways for economic reasons.

A standard lane width of 3.65m has been usedon all typical cross sections illustrated.Exceptions are permitted where it is necessaryto maintain continuity with the remainder of anexisting route, and in new development areassuch as Salwa Industrial Area and the NewDistrict of Doha.

In order to provide adequate drainage, astandard crossfall of 2% has been applied forcarriageways and medians.

Generally the centreline of the maincarriageway shall be iocated on the reservationcentreline. However, should existing or

January 1997

SECTION 5

proposed land use require carriageways to beoffset to one side then approval from theDirector of the Civil Engineering Dept must besought.

In the case of road centrelines being offset fromthe reservation. The utilities layout shall berevised to suit the specific road cross sectionproposed, the revised utility locations to be tothe approval of the Utility Authorities.

If the engineer is unable to utiliserecommendations from the typical crosssections because of existing buildings, buildingusage or land ownership problems, for example,then advice should be sought from the Directorof Civil Engineering Department beforeproceeding.

Certain special routes, such as abnormal orexceptional ioad routes or scenic routes, mayrequire individual reservations to satisfy theirperformance criteria, ego the Corniche. In thesecases, consultation should be sought with theDirector of Civil Engineering Department.

In many areas of existing development, roadcorridor widths or alignment may be restrictedby property ownerships or old planning. Inmany cases, 12m reservation widths were oncethe norm. In these situations the designer mustpay particular attention to many factorsincluding sight distances, clearance at junctions,utility location, reduced carriageway widths,restricted access and road closure.

Page 5/1

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---

SECTIONS

•

January 1997 Page 5/1 0

•


5.2 LANE WIDTHS

Lane widths have a great influence on thesafety and comfort of driving. it has beenshown that undesirable conditions aregenerated on two-lane, two-way, rural roads,carrying moderate traffic, with road widths iessthan 6.5m. Furthermore, it has been shownthat narrow widths severely affect the capacityof a road.

In general, the road width to be providedshould be 7.3m, based on a lane width of3.65m. This provides adequate clearancebetween passing commercial vehicles. Incertain circumstances it may be necessary toincrease the road width to 11.3m. This may beconsidered on local distributor roads to facilitatefuture improvements to turning movements asthe traffic volume increases. This 11.3m widthcomprises two 3.65m wide ianes with anadditional 4.0m to facilitate the turning lane.

The width of turning lanes is discussed inClause 5.10.

Where the road edge is kerbed, thecarriageway should be increased in accordancewith Clause 5.5.

SECTIONS

The use of 4.0m lane widths may be permittedIn particular situations to maintain continuity withthe remainder of an existing route. If the lengthof new road concerned is significant,consideration should be given to adopting a tiein for economic reasons. Where an existingroad with 4.0m wide lane widths is to beredesigned, the lane widths should beredesigned as 3.65m wide.

Generally lane markings should be allowed foras Figure 5.10.

Edge lines - line provided within the edge strip.

Lane lines - included within the carriagewaywidth.

iI

Edge Lane Width , Lane Width Edge

Strip , StripI,

Edge I. 1.1 I. Lano I. Edge

Line 'I '11'1 Line 'I Line,- -!- -I,I,

Figure 5.10 Lane Line / Lane Width Relationship



5.3 LANE CAPACITY

In addition to strategic importance and safety,the desired characteristics of traffic flow willgenerally determine the class of a road. Forexample, high voiumes of traffic are generallyassociated with urban Primary Routes, whereas low volumes are associated with TertiaryRoutes.

SECTION 5

provision sh'ould be made for furtherimprovements to existing sections.

Lane Provision Road Capacity(veh/hour)

Single Lane 1,6002-Lane Dualling 3,2003-Lane Dualling 4,800

•

For detailed assessment of highway capacityand level of service for different roads, refer toThe Kingdom of Saudi Arabia, Ministry ofCommunications, Highway Design Manual,Volume 2, Design of Roadways, Section 1.03.

In most urban situations, the capacity ofintersections on a particular network will governthe capacity of the network as a whole.Uninterrupted flow only takes place when theinfluence of at-grade intersections can beneglected. This is rarely the case on most urbanroad systems.

Table 5.1. Recommended Road Capacity

The capacity of a highway is affected by thecomposition and the habits and desires of thetraffic using the road system and the controlsthat the designer imparts onto the traffic. Theseinclude:

Commercial vehicles

Lane distribution

Variations in traffic flow

Traffic interruptions.

Under ideal conditions, vehicles can follow oneanother at average minimum headways ofabout 1.8 seconds, giving a maximum flow rateof about 2,000 vehicles per hour. A line ofvehicles can start up with an average minimumheadway of about 2 seconds giving a maximumstarting-up rate of approximately 1,800 vehiclesper hour. These maximum rates are reducedby many prevailing road and traffic conditions.

When two or more lanes are available for trafficin a single direction, the distribution in lane-usewill vary widely. The lane distribution willdepend on traffic regulations, trafficcomposition, speed and volume, number andlocation of access points, origin-destinationpatterns of drivers, development, environment,and local driver habits.

Due to the above factors, there are no typicallane distributions. The recommendation for1,600 vehicles per lane per hour recognisesthat flow in some individual lanes will be higherand in others lower. Refer Table 5.1.

5.4 SHOULDERS

The addition of a shoulder to the nearside edgeof a road has many advantages. Shouldersprovide structural support for the pavementedges, emergency parking space for stoppedvehicles and also provide side clearancebetween moving vehicles and stationary objects.They also provide additional running lanes fordiversions and road maintenance. Shouldersare not usually required on urban single andurban dual carriageways as structural support isprovided by the kerbs and channels andstopped vehicles can find a safe place to rest indriveways and side streets. The shoulder maybe paved to the same standard as thecarriageway or of lesser construction such as toroad base construction. The merits of using alesser construction should be consideredaccordingly for each particular situation.

Where there is a high traffic volume, narrowshoulders give very poor service. There is agreater number of accidents and they incurmore frequent and costly maintenance.

In deciding whether to include a shoulder, theengineer should consider the following:

a) Additional width provides a place forsafe stopping because of mechanicaldifficulty, flat tyre or any otheremergency. This also minimisesdisruption to traffic flow.

b) Additional width provides space forincreased mobility to escape potentialaccidents or reduce their severity.

At the planning stage, major routes should beplanned and designed as multi-lane, divided,controlled access facilities even though theymay be developed by staged construction. Inthe plans for each stage of development,

January 1997

c) Stormwater drainage is improved as thewater can be discharged further fromthe running carriageway.

Page 5/12

•

•


d) Additional width increases sightdistance in cuttings and improveslateral clearance to signs and safetyfences.

e) The apparent openness of the insidelane reduces driver stress.

f) A cost benefit analysis should becarried out at the initial schemeassessment phase.

Where shoulders are provided a width of 3.0mshould be used at a standard crossfall of 2percent or as an extension of the crossfall ofthe carriageway.

5.5 EDGE STRIPS AND SHY DISTANCES

Edge StripEdge strips provide a safer carriageway, withimproved drainage and more space to move incase of an emergency. Edge strips keeproadside debris away from the running width ofan outside lane and prevent edge loss on therunning lane.

Edge strips are to be provided on all roadswhich are not kerbed.

A width of O.5m is deemed sufficient for an edgestrip width for a median edge on a dualcarriageway. The edge strip width shall beallowed for within the standard median widthand shall not reduce the lane width. ReferTable 5.2.

SECTIONS

strip there is no need to provide a shy distance.

It is recommended that a shy distance of O.5mshould be added to the road width for eachkerbed road edge on roads with a design speedgreater than BOkph. On kerbed dualcarriageway roads of design speed less than orequal to BOkph, a shy distance of O.35m shallbe added to the outside edge as a gutter. ReferFigures 5.1 - 5.7. The shy distance is anadditional pavement width and the lane widthshall not be reduced. Shy distance at junctionsis discussed further in Section 6.

5.6 MEDIANS

Medians are used to separate opposing trafficlanes on dual' highways. They provideprotection from interference by opposing traffic,minimise headlight glare, provide space forutilities and future lane width, provide additionalspace for crossing and turning vehicles at atgrade junctions, and allow pedestrian refuge inurban areas.

A median may vary in composition from say a1.2m width with a pedestrian barrier to a 20mwide median with street lighting, drainage andlandscaped areas. Medians are dependant onthe width of reservation available and thefunctional requirements of the median. Often,consultation with the relevant planning authorityis required prior to agreement of the width andfunction of the median. Preferred standardmedian widths are given in Table 5.3.

Preferred Standard MedianWidths (m)

Table 5.3

Narrow Intermediate Wide

1.2 4.0 8.02.0 6.0 12.0

NarrowNarrow medians are those in the range 1.2m toless than 4.0m and are used in restrictedconditions. Medians 102m wide do not providea refuge area for pedestrians but do provide theminimum space permitted for clearance ofopposing traffic provided the lane edge Iskerbed. Narrow medians are used where thereis a need to provide a divided road: but wherethe available reservation does not permit agreater median width. Narrow medians are notwide enough to provide effective left turn lanes.The minimum allowable median width to providea safe pedestrian refuge is 3.5m. Pedestriansability to cross at narrower medians shall becontrolled or actively discouraged by theprovision of barriers/high kerbs, continuousplanting and other features.

Edge Strips & Shy Distances

Edge Strip/Shy Distance (m)

Road Type Outside Edge Median Edge

AuralSingle 0.35 -Dual 2 Shoulder 0.5Dual 3 Shoulder 0.5

UrbanSingle . -Dual 2 < 80kph Kerb + 0.35 KerbDual 3 < 80kph Kerb + 0.35 KerbDual 2 > 80kph Shoulder Kerb + 0.5Dual 3 > 80kph Shoulder Kerb + 0.5. ..

Whilst awaIting services and kerbs to be Installed. atemporary edge strip a.35m shall be added to give acarriageway width of 8.0m.

Table 5.2

Shy DistanceWhere a kerb is provided there is a tendency fordrivers to steer a distance away from the kerb,this is termed "shy distance". At slower speedsthe requirement for shy distance is reduced andconversely, at higher speeds, an increased shydistance is required. Where there is an edge



It is not recommended that narrow medians areused on rural roads.

A narrow median should not be considered if itis possible to provide an intermediate or widemedian at that particular location. Acceptablestandards for the remaining cross sectionelements should be maintained.

IntermediateIntermediate width medians are those in therange 4.0m to less than 8.0m and are generallywide enough to provide for a left turn lane. Awidth of 8.0m is the desirable minimum toprovide a left turn lane and a residual median,and a width of 8.0rn is the desirable minimum toshelter a crossing vehicle undertaking a U-turnmanoeuvre.

WideMedians 8.0m or greater in width provide spacefor effective landscaping and may be used forsigning, services and drainage. Wide mediansmay aiso be used to absorb level differencesacross the road reserve. Rural medians shouldbe a minimum of 8.0m wide with a central safetybarrier.

A disadvantage of wide medians occurs atsignalised junctions, where the increased timefor vehicles to cross the median may lead toineffective signal operation.

Wide medians should not be impiemented atthe expense of reduced verge widths. Vergewidths are required for pedestrian walkways,installation of services, traffic signs, drainagechannels, parking etc. Any significant reductionin verge width may result in hazards in theverge which negate the advantages of a widermedian.

It is recommended that urban medians shouldbe kerbed and that rural medians should beprovided with an edge strip and not kerbed. Akerbed median is desirabie where there is aneed to control left turn movements and is aisoused when the median is to be landscaped. Inthe rural situation, a depressed median ispreferred as this improves drainage of the road.

Special attention should be given to drainage ofmedians. If the median is kerbed, the mediansurface should be designed to have slopes of 2percent, and should fall towards the centre ofthe median if unpaved, or slope out if paved.Depending on whether the median is paved oropen, or planted or not, the drainage should notinterfere with the operation of the highway.Paved medians may require positive drainagesystems incorporating manholes, pipes etc.Non-paved medians may be self-draining, but

January 1997

SECTIONS

again, consideration should be given to theprovision of additional storage capacity oroutlets to allow for storm conditions. Alldrainage inlets in the median should bedesigned with the top flush with the ground, andculvert ends provided with safety grates so theywill not be hazardous to out of control vehiclesthat run off the road.

It is common practice to landscape medians.This is seen to provide a better environment andreduce driver stress. Careful considerationshould be given to the choice of planting toensure that visibility and stopping distances arenot impaired. Furthermore, the upkeep of thelandscape and growth of the plants should bedesigned for minimal maintenance and henceless disturbance to the road user.

Watering shall not require tankers to obstructthe trafficked lanes at any time.

Where two abutting sections of highway havedifferent carriageway widths it is desirable that asmooth transition should accommodate thisdifference. The transition should be as long aspossible for aesthetic reasons and preferablyoccur within a horizontal curve.

5.7 VERGES

The verge is a width of the reservation whichfacilitates additional functions essential for theoperation of the road. As a minimum vergesmust be able to accommodate highway signs,structures, utility services such as water,electricity, Q.TEL, drainage, and additionallysuch items as traffic signals and street lighting.Where a verge is adjacent to a development aset back may be required. Verge widths mayvary from a desirable minimum of 3.0m up to thelimits of the reservation, which could be inexcess of 15.0m. Paved verges should bedesigned with a 2% fall towards the carriagewayfor drainage purposes. However, in largerpaved areas, falls shall be designed to specificdrainage collection points in the verge.

It is important to ensure that whatever isinstalled in the verge (such as structures, signsor landscaping) does not affect the sightdistances required for the particular designspeed of the road. Additional care should alsobe taken at traffic signals and junctions wheremore signage is implemented.

Verges may be paved, landscaped or gradeddepending on the intended use of the verge.

It may be necessary to increase the verge widthif soakaways are to be installed within the verge.

Page 5/14

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5.8 PARKING BAYS AND LANES

H

Interlock 10 KerbModul.

xv

InterlockingModula

G

Parking Bay Dimensions (m)

Parking Bay Dimensions for3.0m x 8.0m Stalls

C D E

F

/-

W.ltle InterlockModule

Table 5.4

Dimension On AngleFigure

5.9 45" SO' 75' 90'

Stall width, parallel A 4.25 3.50 3.25 3.0010 aisle

Staillengih alline B 9.00 7.75 6.80 6.00

Stall depth to wall C 6.40 6.70 6.60 6.00

Aisle width belween D 4.50 5.00 7.10 8.00slaillines

Stall depth interlock E 5.30 5.95 6.20 6.00

Module, wall to F 16.20 17.65 19.90 20,00interlock

Module, interlocking G 15.10 16.90 19.50 20.00

Bumper overhang H 0.60 0.70 0.75 0.75(lypical)

Figure 5.9

DimenSIons for 3m by 6m stalls

x • SloU nolDvellable In clltlaln loyout_

Service Road ParkingIf there is sufficient reservation width,consideration should be given to the provision ofa service road to access either a parking lane,parking bays or designated car park. Thisresults in a safer highway and fewerinterruptions to through traffic, and enables flowto be maintained more easily. Refer to Clause5.11 for service roads.

SECTION 5

Parking on Access RoadsWhere residential development is dense and therequirement for additional on-street parking islikely, then the standard parking lane width of2.5m shall be used. The minimum parking lanewidth is 2.2m. The designer should bear in mindthat the very low number of vehicles usingaccess roads means occasional on-streetparking by visitors or delivery vehicles wiil notcause congestion. In fact, their presence willhelp to keep the speed of other vehicles low.

of utilities to bebe made at the design

Due investigationaccommodated shallstage.

Where possible, parking shall be provided awayfrom the carriageway and in convenientlylocated, specific iots or along service roads.Parking shouid not be provided near junctionsor opposite access points as this is likely toincrease the probability of accidents and alsohinder sight distance.

Parking Lanes (parallel parking)Parking lanes may be provided adjacent to theinside lane of the carriageway (ie. the slowiane). The standard width required for a parkinglane is 2.5m, each bay being nominally 8.5m inlength. Care should be taken when providing aparking lane to ensure that the design speed isappropriate to allow a safe stopping distance, iffor example, a passenger were to accidentallystep into the carriageway whilst embarking ordisembarking a vehicle. It is recommended thatparking lanes should only be provided on singlecarriageway roads, with posted speeds of 50kph or less. The lane provision, design speed,stopping sight distance and traffic volumesshould also be appropriate to allow minimalinterruptions to traffic flow when vehicles areentering or leaving the parking lane.

The need for parking is determined by theexisting and future deveiopment of theimmediate surrounding area. Consultation willbe required with the Traffic Section and thePlanning Department to determine the future.development plans and the amount of on-streetand off-street parking required.

Provision for parking is achievable by thefollowing methods.

Parking Bays (angled parking)If the width of available reservation allows,consideration should be given to the provision ofparking bays. Parking bays should not bepermitted on the main through carriageway ofdual carriageways. The perpendicular parkingbay should be made up of stalls 3.0m wide and8.0m in length. The dimension requirements forangled parking are shown in Tabie 5.4 andFigure 5.9. Parking in bays requires greateradjacent lane width to accommodate the turningmovement depending on the choice of parkingangle.

•

•


*In all cases parking must not encroach on visibility splays.


5.9 SIDE SLOPES

• Bends; to maintain adequate forwardvisibility for drivers

•

,.'.

SECTION 5

Cut and fill slopes should be flattened asappropriate with the topography and beconsistent with the overall type of highway. Theintersection of slope planes in the highway crosssection should be well rounded to simulatenatural earth forms. The rounding and flatteningof slopes minimises drifting and wash out ofloose material such as sand and hence reducesmaintenance costs.

It is recommended to carry out an adequategeotechnical investigation prior to specifyingslopes. The investigation will determine themaximum slopes for cut and fill and the criteriafor benching or erosion protection if required.

In rock cuttings it is recommended to includeditches and a debris verge to provide a safelanding and catchment area for possible rockfall. and removal of surface water run off. Thisadditional width also provides a useful area forrock face maintenance. It is becoming commonpractice in the UK for rock outcroppings to beleft in place for reasons of economy oraesthetics. This may be considered forapplication in Qatar. However in such situationsthis may prove lethal if a vehicle were to collidewith the outcrop. It is recommended that at allsuch locations a safety fence be prOVided.Refer to Clause 5.15 for safety fences.

Benches should ideally be 4.0m in width andlaid to falls of approximately 1 in 20 to avoidponding of water and consequential slip failure.

1..-_ .

Typical Parking LaneTreatment at T-Junctions.

Pedestrian crossing points; to minimisecrossing width and enable crossingpedestrians to be seen clearly bydrivers

Any other location where parking wouldcause unsafe conditions.

.............).

•

•

Figure 5.10

• Junctions; to provide space forpedestrians to cross and to maintainadequate visibility. See Figure 5.10

----_._._--------._._-------j-_.------_._._---------_._.-.............. l.---j ~'5··Ty~_? l----j j

5.0m m'n:7 1 I ( ""s.om min. Parking

;;

!

Parking ExclusionsParking shall be excluded from the followinglocations:

Side slopes fall into two categories.embankment and cutting. They serve two mainfunctions; firstly they provide structural stabilityto the road, secondly they provide a surface onwhich out of control vehicles may travel andrecover, minimising the chance of overturning.

For details of sand slopes, wind blown sand anddune control refer to the Kingdol)l of SaudiArabia. Ministry of Communications. HighwayDesign Manual. Book 2, Section 1.16, SandDune Control.

Where possible the side slopes should fall awayfrom the verge at a slope of 1 in 5. It is usual toconsider the provision of a safety fence whenslopes are steeper than 1 in 5 and/or the heightof the slope is greater than 6m. Safety fencingis discussed in Clause 5.15. Generally, it isbetter to use flatter slopes, proViding there isadequate fall for drainage. Slopes in cuttingshould not be steeper than 1 in 2 and preferablyshould be 1 in 3 to allow mechanicalmaintenance equipment to be used on theslope. If there is insufficient width which wouldrequire siopes. steeper than 1 in 2. then partialor fUll retaining walls should be used or somemethod of slope stabilisation. Retaining wallsshould be set back from the carriageway toavoid a constricting feeling and reduce stressfor the driver.


QATAR HIGHWAY DESIGN MANUAL SECTIONS

5.11 SERVICE ROADS

S=NU30

For further details of junction design and lanecapacity refer to Section 6 Junctions and theQatar Traffic Manual.

Service roads may also provide an alternativeroute if maintenance is required on the throughroad or in case of an emergency..

Storage length (m)Design volume of turningvehicle (vehicles per hour)Length in metres occupied byeach vehicle (7m for passengervehicles, 12m for trucks)

L =

Where S =N =

Service road connections to the main roadshould be designed as at-grade junctions inaccordance with the guidelines given in Section6 Junctions.

The width of the servjce road is dependant onthe classification of traffic expected to use theservice road such as light vehicles, deliverylorries or heavy goods vehicles. Furtherconsideration should be given to the turningrequirements of such vehicles, the type andnumber of access points and type of streetparking, if required.

Where one-way service roads'are to be installedwithin the reservation the absolute minimumwidth of outer median permitted is 1.2mprovided no signing is required. This distanceallows for the provision of a central pedestrianbarrier only. if traffic signs are required or otherstreet furniture the desirable minimum width is2.1 m. A wider outer median is preferred, butthis will depend on the width available within thereservation. Wider outer medians give greaterscope for landscaping which enhances theappearance of both highway and the

Service roads provide a number of functionsdepending on the deveiopment of thesurrounding area. The provision of serviceroads reduces the number of access points ontothe main highway and segregates the higherspeed through traffic from the lower speed localtraffic. This reduces interruption of traffic flow,makes the best use of road capacity and resultsin a safer road.

Service roads are roads which run roughlyparallel with, and are connected to the mainthrough highway. They are generally of lowdesign speed and preferably restricted to oneway traffic. Figure 5.7 shows a typicalreservation with a service road.

5.10 AUXILIARY LANES

Auxiliary lanes serve as speed change lanes,storage lanes or a combination of the two. Theymay also be either right turn or left turn facilitiesat junctions (refer to Section 6 Junctions). Aspeed change lane is primarily for theacceleration or deceleration of vehicles enteringor leaving the through traffic lanes. A speedchange lane should be sufficient in length andwidth to enable a driver to make the necessarychange between the speed of operation on thethrough highway and the lower speed necessaryto turn, with minimal disruption to the speed offollowing vehicles. Speed-change lanes canhave different layouts depending on thealignment of the highway, frequency ofintersections and the distance required to effectthe necessary change of speed.

Deceleration LanesA deceleration lane consists of a taper and a fulllane width. The length of deceieration lanesshould be determined according to the designspeed of the highway and the design speednecessary to make the turn. The greater thedifference between these speeds the ionger thedeceleration lane should be. Deceleration laneson approach to at-grade intersections can alsofunction as storage lanes for turning traffic.

Refer to Section 6 Junctions for further detailson the following topics.

Acceleration LanesDesign considerations for acceleration lanes aresimilar to those for deceleration lanes.Acceleration lanes are provided to permit anincrease In speed before entering the throughtraffic lanes and also to serve as manoeuvringspace, so that a driver can take advantage of anopening in the adjacent stream of through-trafficand join it.

Left and Right Turn LanesThe provision of separate left and right turninglanes should be determined by a capacityanalysis for the junction under consideration.Acceleration and deceleration tapers should beused with these turning lanes. The length ofturning lanes shall depend upon the lengthrequired for speed change and the number ofvehicles to be stored. Typically the storagelength is based on the number of vehicles thatare likely to accumulate in two minutes, asdetermined by the capacity analysis, and Iscalculated by the following formula:

•



appearance of both highway and thedevelopment adjacent to the highway.

Refer to HMSO pUblication, Designing forDeliveries for detailed explanation andgUidelines of requirements for serviceroads/areas, and turning movements fordifferent vehicle types.

5.12 PEDESTRIAN FACILITIES

Pedestrian facilities are generally found withinthe verge and at road crossing points. Theprovision of paved pedestrian areas is related tothe function of the roadside development. It isoften difficult to obtain reliable estimates ofpedestrian volumes and movements. For thisreason, studies should be carried out at theconcept and preliminary design stage. All urbanroads and junctions shall allow space forfootpaths unless the area strictly forbidswalking. A width of 2.0m should be provideddepending on pedestrian needs. The width ofpaved pedestrian areas should be increased toa minimum of 3.0m near schools, large sportsvenues, commercial areas or other areas withhigh pedestrian volumes. Footpaths may beconstructed of paving blocks or concrete andlaid to crossfalls of 2% towards the roadway topermit drainage.

Where possible a separation area should beincluded within the verge which acts as a bufferbetween vehicular and pedestrian traffic. Theseparation width should be designed todiscourage pedestrians from standing at thekerbside. This is achievable by providing anumber of obstacles such as low planting,raised blockwork or pedestrian barriers. Aminimum separation width of 1.2m is desirable.A separation width is not required in commercialareas with on street parking where widerfootpaths are usually provided.

Pedestrians should be activeiy discouragedfrom crossing roads along the length of dualcarriageways. Special pedestrian refugesections should be provided at selected points,or ideally at junction locations. It isrecommended that these refuge areas be aminimum of 3.5m wide and should be staggeredso that pedestrians are not able to approachand cross both carriageways in one line.

On roads with a posted speed of 60kph or less,it is recommended to provide a pelican crossing(signaiized pedestrian crossing) or a zebracrossing (pedestrian crossing defined by roadmarkings) as a crossing point for pedestrians.These crossings should be located, signed andmarked in accordance with this manual and withthe Qatar Traffic Manual.

January 1997

SECTION 5

In areas with high volumes of pedestrian traffic,footpaths should be provided on both sides ofthe road. Some urban areas and most frontageroads can be served with a footpath on one sideonly. In these areas, footpaths must becontinuous for the full pedestrian route.

On rural roads, footpaths are not usuallyrequired, except along sections of road wherethere is sUbstantial residential or commercialdeveiopment. In such situations, footpaths areusually located between the bottom of theembankment and the property line.

Pedestrian RampsIn order to provide adequate and reasonableaccess for the safe and convenient movement ofpedestrian and handicapped persons, includingthose in Wheelchairs, kerb ramps should beincluded at all pedestrian crossing points. Kerbramps should be at least O.9m in width, slopedat the rate of 1 in 12 or flatter, and located onthe pedestrian side of the kerb face.

The edge of the ramp facing the carriagewayshall be flat and set 25mm above the level of theroad pavement. Drainage equipment such asgratings should not be placed in ramp areaswhere they may caused a hindrance towheelchairs.

Structures for Pedestrian MovementsThe need for a pedestrian grade separatedstructure such as a footbridge or underpassmust be investigated in some depth for eachparticular situation. The investigation shouldcover studies of pedestrian generating sources,travelling patterns, crossing volumes,classification of road to be crossed, land use,location of adjacent crossing facilities, and socialand cuitural factors. The structure to be providedmust accommodate handicapped pedestriansand those with wheelchairs. Ramps should beprOVided to a preferred grade of 1 in 12.However, a maximum grade of 1 in 10 may beused in difficult locations. Level landing areas of1.5m length should be installed such that noindividual ramp section is longer than 9.0m.Handrails should be provided on all steps andramps. The width of the walkway should be aminimum of 2.5m between walls or railings. Itmay be necessary to install pedestrian barriersin the vicinity of the structure to deterpedestrians from crossing the road at-grade.

A pedestrian overstructure is preferred to anunderpass. An over structure should bedesigned to be in keeping with the surroundingarea in terms of geometry and architecture. Therequired headroom clearance for overstructuresis detailed in Clause 4.6. Lighting and fencingshould be considered on a site by site basis.

Page 5/18

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•

•

•


Pedestrian underpasses shall be well lit withclear unobstructed visibility. A pavement orramp approaching an underpass should providea clear view through the underpass. Thedesirable headroom clearance through theunderpass is 3.0m.

Specific consideration needs to be given to thedrainage of underpasses both for the removal ofrainwater and effects of high groundwaterlevels.

5.13 UTILITIES

Road corridors are given in Figures 5.1-5.9.These are intended to provide adequate spacefor road cross section requirements and at thesame time allow the public utilities sufficientspace for existing and proposed plant. Wherespace for utilities is limited, "wayleaves" outsidethe road reservation may be obtained bycontacting the planning department.

The pUblic and private utilities to beaccommodated include the following:

Telephone (Q.TEL)

Cable television

Electricity - distribution

Electricity - lighting

Electricity - transmission

Sewerage

Return effluent

Surface water and land drainage

Water

Oil and gas.

Each utility has their own working proceduresand works specifications. These shall bereferred to when designing the roadconstruction and drainage facilities.

Particular consideration may be required toposition soakaways if the reservation width isrestricted. Refer to the typical cross sectionsshown in Figures 5.1 to 5.7. Where space islimited, soakaways may be lowered, by theaddition of rising sections, to allow shallowutilities such as Q.TEL to pass above thesoakaway chamber. However, in new roads,priority is to be given to road related utilities, egodrainage, lighting etc.

January 1997

SECTION 5

5.14 USE OF KERBS

There are a number of types and combinationsof kerbs available, each with particUlarapplications. Some of the details in regular useare listed beiow.

Raised kerb

Raised kerb with channel block

Edge kerb

Channel block

Flush kerb

Dropper kerb

Dropped kerb

Vehicle barrier unit (VBU).

The standard kerb unit is available in a range ofsizes and shapes. The shape is varied toenable kerbs to be installed on a range of radii.It is recommended to check the availability anddimensions of kerbs with the manufacturer as afull range may not be available in Qatar.

Kerbs provide a number of functions which are:to define and provide structural support to theedge of carriageway; to control highwaydrainage; to segregate vehicles andpedestrians.

Kerbs are to be used on all urban roads andonly at special locations on rural roads, such asjunctions where there is a need to give a cleardelineation of the road edge.

Where there is a need to install a safety fencealongside a kerbed section of road, the fencedesign, kerb design and drainage design shouldbe carried out together. The kerb may affect thechoice of safety fence type, and it is important toensure that the combined drainage/kerb facilitydoes not reduce the safe operation of the safetyfence.

Page 5/19


5.15 SAFETY FENCES

GeneralA safety fence is a longitudinal barrier used toshield motorists from natural or man-madehazards located along a road. It may also beused to protect bystanders, pedestrians andcyclists from out of control vehicular traffic.Safety fences may be located in the verge ormedian depending on the particuiarrequirements and location. Refer to Figure 5.11for the definition of terminology used in safetybarrier design.

The safety fence is designed to prevent anerrant vehicle from leaving the carriageway andstriking a fixed object or feature that isconsidered more hazardous than the barrieritself. This is accomplished by containing andredirecting the errant vehicle.

On a divided road, a safety fence is located inthe median to separate opposing traffic.

Safety fences should only be installed if theyreduce the severity of accidents. This mayappear subjective, but generally a barrier shouldbe provided if the consequences of a vehiclestriking a fixed object, or running off the roadare determined to be more serious than hittingthe safety fence itself. Other considerations aretraffic speed and traffic volumes and a costanalysis.

The cost analysis is based on:

• Removing or reducing the hazard sothat it no longer requires protecting

• Installing an appropriate safety fence

• Leaving the hazard unprotected.

Median safety fences are generally providedwhere the median width is relatively narrow andthe traffic volumes and speeds are high. Theymay also be provided where the separatedcarriageways are at different ievels, as thelikelihood of an accident increases the steeperthe slope between carriageways. It is importantto provide gaps in the median fencing foremergency use and maintenance.

EmbankmentsEmbankment height and side slope are factorsin determining safety fence need. The provisionof safety fencing should be considered whenslopes are steeper than 1 in 5 and/or the heightof the slope is greater than 8m, refer to Figure5.12. Rounding slopes reduces the chances ofan errant vehicle becoming airborne. Theoptimum rounding may be defined as being the

January 1997

SECTION 5

minimum radius a standard size car cannegotiate without losing tyre contact. This isdependant on approach angle and speed aswell as the characteristics of individual vehicles.

Roadside ObstaclesA safety fence should only be installed if it isclear that the result of a vehicle striking thebarrier will be less severe than the accidentresulting from hitting the unprotected object.

Generally, if an object is greater than 10mfrom the travelled way, it does not requireprotection.

Table 5.5 summarises of the various needs forsafety fencing.

PedestriansThe most desirable solution to protect theinnocent bystander is to separate pedestriansand vehicuiar traffic. If this is not achievablethen consideration of safety fencing shouid begiven at schools, busy commercial and retailcentres, sports venues and other locationswhere high pedestrian movements areanticipated or observed.

Page 5/20

•

•

" •o

~:IlJ:isJ:

~om(j)

iszs::I>ZC:I>I""

ent

Uostreamal

uHazard or

inalLength of Need other Feature Length of Need

Termind Standard Section or End

Iment Standard Section Transition or Bridge Rail Transition Standard Section Trealn

DownstreamTermor ETrea

c.. JJIII::J

CO

Cc~

III CD~

'< ~..... .....<D

.....<D-..j 0

!ll.5"

""0"::J

sa.(j)

a~"T1CD::J

"CD

mro3CD:::len

Edae of PavementSetback/Clearance to Edge of Pavement

Direction of Travel(adjacent traffic)

FlareRate

Direction of Travel(opposing traffic)

~co

CDen~.....

(j)m

~oZen


•TR:~i~~~~~~:Li2??r/ ;H~LL:tJSECTION EMBANKMENT

R~ _ R 'HEIGHTY ~'----

R=ROUNDING

18m15m12m6m 8m

Height (m)

Barrier not Required for Embankment.However, Check Barrier need for otherRoadside Hazards.

3m

•Om

1:1

1:2

1:10

1:1.67

~

>- 1:2.5..~Q)0-.9CJ)

c:1:3.30

tiQ)

CJ)

u:::

1:5

Figure 5.12 Requirement for Safety Fences on Embankments

January 1997 Page S/22


Types of Standard Sections of Safety FenceSafety fencing is usually classified as flexible,.semi-rigid or rigid.

Flexible systems are generally more forgivingthan other categories, as much of the impactenergy is dissipated by the deflection of thebarrier and lower impact forces are imparted onthe vehicle. There are two basic types offlexible system:

The first is a cabled fence, normally comprising4 strands of tensioned cable. Cable fencesredirect impacting vehicles after sufficienttension is developed in the cable, with the postsin the impact area providing only slightresistance. The cable fence returns to itsoriginal position and damaged posts are easilyreplaced.

The second type utilizes a standard steel beamsection mounted on relatively weak posts. Thissystem acts in a similar manner to the cablesafety fence. It retains some degree ofeffectiveness after minor collisions due to therigidity of the beam rail element. However, aftermajor collisions it requires full repair to remaineffective. As with the cable system, lateraldeflection can be reduced to some extent bycloser post spacing. This system, as with allbarriers having a relatively narrow restrainingwidth, is vulnerable to vaulting or vehicle underride caused by incorrect mounting height orirregularities in the approach terrain.

Semi Rigid Systems work on the principle thatresistance is achieved through the combinedflexure and stiffness of the rail. Posts near thepoint of impact are designed to break or tearaway, distributing the impact force to adjacentposts. Deflection of this type of beam is up toapproximately 1.5m (test data; 26 degrees,95kph, 1.8 Tonnes)

Strong post fences usually remain functionalafter moderate collisions, thereby eliminating theneed for immediate repair. There are a numberof different types of semi rigid fence on themarket, each system having its ownperformance requirements and capabilities. Afew examples are listed below:

SECTIONS

The self-restoring safety fence is a highperformance fence designed to bemaintenance free for most impacts and capableof containing and redirecting large vehicles.The combination of high initial cost and highperformance makes this barrier more suited foruse at high accident frequency locations.

When traffic speeds are expected to be greaterthan 50kph the semi rigid system should betensioned. Tensioned systems usually requirea minimum length to be effective and areunable to be installed on sharp radii (typically50m length and 150m minimum radii).Individual barrier manufacturers specificationsshould be adhered to.

Object Comment

Bridge piers, Protection generallyabutments and railing reqUiredends

Culverts, pipes, Judgement required basedheadwalls on size, shape and location

of hazard

Cut slopes (smooth) Generally protection notreqUired

Cut slopes (rough) Judgement required basedon likelihood of impact

Ditches (transverse) Generally protectionrequired, ditch profile to beconsidered

Embankments JUdgement required basedon height and slope

Retaining wall Judgement required basedon relative smoothness andanticipated maximum angleof impact

Signs and luminalrs Generally protectionsupports required for non-breakaway

supports

Traffic signals Isolated traffic signals onhigh speed rural roads mayrequire protection

Trees and utility poles Protection may be requireddepending on site by siteconditions

Permanent bodies of Judgement reqUired basedwater on deptfl of water and

likelihood of encroachment

Box Beam

Open Box BeamTable 5.5 Consideration forthe Provision

of Safety Fencing

W-Beam (corrugated type of fence)

Blocked Out W-Beam

Self-Restoring Safety Fence

January 1997

Rigid Systems offer no deflection when hit bya vehicle. The impact energy is absorbed bythe vehicle. For high angle and high speedimpacts, passenger size vehicles may becomepartially airborne and in some cases may reachthe top of the barrier. For shallow angle

Page 5/23


impacts, the roll angle toward the barrierimparted to high centre of gravity vehicles maybe enough to permit contact of the top portion ofthe vehicle with objects on top of or immediatelybehind the fence, ego bridge piers. Commonlyused rigid systems are the New Jersey Barrier inthe USA, and the British Concrete Barrier in theUK.

Typically the system is relatively low cost, hasgenerally effective performance for passengersized vehicles and has maintenance-freecharacteristics.

End TreatmentsThe untreated end of a safety fence is extremelyhazardous If hit, as the beam element canpenetrate the, passenger compartment and willgenerally stop the vehicle. A crashworthy endtreatment is therefore considered essential if thesafety fence terminates within 10m of thetravelled way and/or is in an area where it islikely to be hit head-on by an errant vehicle. Thetermination of the safety fence should not spear,vault or roll a vehicle for head-on or angledimpacts. For Impacts within the length of need,the end treatment shouid have the sameredirectional characteristics as the standardsafety fence, which means that the end must bealso properly anchored.

There are a number of different types of endtreatments which work on a range of principles,some of which are listed below:

Breakaway Terminals

Turned Down Terminals

Energy Absorption Systems

Special Anchorage for Cable Fence

Anchorage into Embankment

Further reference is essential to select the mostappropriate system for each particular situation.

TransitionsTransition sections of safety fence arenecessary to provide continuity of protectionwhen two different barriers join, when a barrierjoins another barrier system (such as a bridgerail) or when a roadside barrier is attached to arigid object (such as a bridge pier).

The transition section should be the samestrength or stronger than the two systems.

The transition should be long enough so thatsignificant changes in deflection do not occurwithin a short distance. Generally the transition

January 1997

SECTION 5

length should be 10 to 12 times the differencein the lateral deflection of the two systems inquestion ego for a beam deflection of 1.5m thetransition should be around 15m.

Drainage features such as ditches should beavoided at transition positions as they mayinitiate vehicle instability.

The stiffness of the transition should increasesmoothly and continuously from the less rigid tothe more rigid system. This can be achievedby decreasing the post spacing, increasing postsize or strengthening the rail eiement.

Selection of Safety FenceThe selection process is not easily defined butthe most desirable system is one that offers therequired degree of protection at the lowest totalcost. Table 5.6 summarises the factors to beconsidered.

Page 5/24

.,

e'


Criteria

b) Collision

d) Simpiicity

c) MaterialsStorage

Desirable Lateral Clearancefor Safety Barriers from Edgeof Travelled Way.

Design Speed Setback from Edge ofPavement (m)

140 3.7120 3.0100 2.580 2.070 1.760 1.550 1.0

. ,

Table 5.7

Barrier Typ'e Clearance from Back ofFence to Hazard (m)

Tensioned wire rope 2.0

Tensioned beam 1.2

Box beam 1.2

Rigid O'. ..Mimmum clearance of objects behmd the barner to

travelled way must be maintained.

Note. Rigid system IS not recommended for design speedsgreater than 100kph

PlacementLateral offset: As a rule, safety fences shouldbe placed as far from the travelled way asconditions permit. This gives the errant driverthe best chance of regaining control of thevehicle without having an accident. It alsoprovides better sight distance. Table 5.7 givessuggested lateral offsets related to the designspeed. Other factors may override thesesuggested figures.

The desirable minimum distance between backoffence and rigid hazards should not be lessthan the dynamic deflection of the safety fencefor impact by a vehicle at impact conditions ofapproximately 25 degrees and 100kph.

Specific manufacturers requirements must befollowed. However, as a guideline, theclearances set out in Table 5.8 are typical.

Fence must be structurallyable to coniain and redirectdesign vehicle

Simpler designs cost less andare more likely to bereconstructed properly on site

Generally, flexible or semi-rigid systems requiresignificantly moremaintenance after a collisionthan rigid or high performancefences

Slope approaching the fenceand distance from travelledway may preclude use ofsome fence types

The fewer the differentsystems used the fewerinventory items and storagespace required

Fence must be compatiblewith planned end anchor andcapable of transition to othersafety fence systems

Expected deflection of fe'nceshould not exceed availableroom to deflect

Comments

Standard fence systems arerelatively consistent in cost,but high performance railingscan cost significantly more

Few systems require asignificant amount of routinemaintenance

Occasionally safety fenceaesthetics are an importantconsideration in its selection

The performance andmaintenance requirements ofexisting systems should bemonitored to identify problemsthat could be lessened oreliminated by using a differentfence type

Deflection

PerformanceCapability

Site Conditions

Compatibility

Cost

Aesthetics

FieldExperience

2

3

4

5

6 Maintenance:a) Routine

7

8

•

•

Table 5.6 Selection Criteria for SafetyFences

Table 5.8 Typical ManufacturersClearance Requirements

On embankments care should be taken toensure that at full deflection of the fence thewheels of the vehicle do not overhang the edgeof the siope.

The combined use of kerbs and flexiblesafety fences together should be avoided.The use of kerbs and semi-rigid or rigidsafety fences should generally be avoided.However, if the face of the safety fence iswithin 225mm of the kerb face, a vehicle isnot likely to vault the fence.



A safety fence is considered flared when it is notparallel with the carriageway. Flare is normallyused to locate the barrier terminal section furtherfrom the carriageway, to minimise a driver'sreaction to a hazard near the road by graduallyintroducing a parallel safety fence installation, toconnect a roadside barrier to a hazard nearerthe carriageway such as a bridge parapet orrailing, or to reduce the total length of railneeded. Reference Figure 5.11.

Flare rates are a function of design speed andsafety fence type. Bearing this in mind, Table5.9 shows typical flare rates.

These installations will require upgrading tocurrent standards and each installation shouldbe considered on a site by site basis.

For further reference on the different types ofsafety fencing refer to the British Department ofTransport document TD 19/85, Safety Fencesand Barriers, and the American Association ofState Highway and Transportation OfficialspUblication, Roadside Design Guide. Fordetails of specific safety fences themanufacturers' technical literature should bereferred to.

5.16· CRASH CUSHIONS

•

Crash cushions or impact attenuators areprotective devices designed to prevent errantvehicles from impacting fixed object hazards.This is achieved by gradually slowing down avehicle to a safe stop (from possible head-onimpacts) or by redirecting a vehicle away fromthe hazard (for side impacts). Crash cushionsare ideally suited for use at locations wherefixed objects cannot be removed, relocated ormade to breakaway, and cannot be adequatelyprotected by a normal safety fence.

Design Flare Rate Flare Rate for FenceSpeed for Fence beyond Setback(kph) within

Setback Rigid System Semi-rigid1:x System

140 1:35 1:23 1:17120 1:30 1:20 1:15100 1:26 1:17 1:1380 1:21 1:14 1:1170 1:17 1:11 1:960 1:13 1:8 1:7.Refer to manufacturers techmcal literature for special

conditions.

The length of safety fence required should besuch that it protects the vehicle for the full extentof the hazard. This includes the length of theapproach flare, the length of the hazard and therunout length beyond the hazard. The runoutlength is particularly important on singlecarrlageways where protection is required forvehicles travelling in the opposite lane.

Existing SystemsWith the development of technoiogy andunderstanding of this sUbject, it is a fact thatolder installations are sUb-standard and do notalways meet current recommended performancelevels. These deficiencies usually fall within twocategories, those that have structuralinadequacies and those that are improperlydesigned or located.

Underground ObstructionsWhere there is a risk of driven posts or standardconcrete footings interfering with cables, ductsand pipes and the alignment of the safety fencecannot be adjusted to avoid the obstruction, orthe depth of pavement construction is such thatthe standard driven post or concrete footingwould not penetrate into the subgrade, specialposts or footings shall be provided with theapproval of the Director of Civil EngineeringDepartment.

Table 5.9 Typical Flare Rates Crash cushions primarily serve to iessen theseverity of accidents rather than to preventthem from happening.

Crash cushions work on one of two principles,either absorption of kinetic energy or transfer ofmomentum. In the first instance the kineticenergy of a moving vehicle is absorbed bycrushable materiais. This can be achieved bythe use of water filled containers. Crashcushions of this type require a rigid back stop toresist the impact force of the vehicle.

The second concept involves the transfer ofmomentum of a moving vehicle to anexpendable mass of material or weights. Thismay be sand filled containers. Devices of thistype require no rigid back stop.

The design procedure is relatively straightforward and basically relates to the number ofcrash cushion units being able to slow down adesign vehicle, at a design speed under anacceptable deceleration force. Mostmanufacturers have design charts to select anappropriate layout.

The most common application of crashcushions is at an exit ramp at an elevated ordepressed structure, where a bridge pierrequires protection. However, they may alsobe used at temporary road works or used toslow a vehicle down on a slope when thebrakes have failed. For optimum use, thecrash cushion should ideally be placed on arelatively flat surface. Kerbs should also be


•


avoided as this may cause the vehicle tobecome airborne.

The effective use of crash cushions is restrictedto cars travelling up to speeds of 100kph, andnot applicabie for large trucks and buses.

There are many different manufacturers of crashcushion systems, each with there own particularmerits and applications. However, the engineerin the selection process must consider the sitecharacteristics, cost, maintenance and thestructural and safety characteristics of thedifferent systems.

For further reference on the different types ofcrash cushions refer to the AmericanAssociation of State Highway andTransportation Officials publication, RoadsideDesign Guide. For details of specific crashcushions, manufacturers technical literatureshould be referred to.

5.17 FENCING

There are many different types of fences usedwithin the road reservation, each type havingparticular applications. The main types offencing are listed below:

• Right of Way Fencing to delineate andseparate private property from the roadreservation

• Safety Fencing erected whereconsidered necessary. Refer Clause5.15

• Animal Fencing prevents animals fromentering the highway reservation. Thesize and type of fencing is dependanton the type of animal the fencing isintended to control, ego camel or goat

• Acoustic Fencing may be required insensitive locations such as residentialareas to lower the traffic noise level.The fence forms a barrier and thesound is reflected away from thesensitive area

• Headlight Barriers may beimplemented at locations where it isdesirable to minimise the glare of theheadlights of oncoming vehicles, suchas at unlit bends on rural roads

• Pedestrian Access Fencing may berequired where there are significantnumbers of pedestrians such as oncommercial streets, outside schools or

January 1997

SECTION 5

large sports complexes where crowdsmay gather. The fencing controls themovement of pedestrian traffic andlowers the risk of a pedestrianaccidentally moving onto a livecarriageway.

5.18 ROAD CLOSURE AND PARTIALCLOSURE

The main aims of full or partial road closure areto:

• Deter non-access traffic from usingresidential roads as through routes

• Limit the number of minor accessesonto major routes

• Remove the crossroad type junctionwhich is generally considered unsafe.Refer Section 6 Junctions

Although these aims are common to the designof new roads, the approach here is different asestablished route patterns, many having beenin use for years, have to be broken andreformed elsewhere. Provision of clear,concise warning and/or diversion signs areadvised during the first two to three months ofoperation. This will help re-educate the driverwho was familiar with the old road layout.

The most basic way to prevent traffic using aparticular route is to close the road, either at aparticular point or along a certain length. It isusual to close a road at an existing junction, ie.at the end of a block of properties, unless theblock is very long, ego 250-300m, in which case"No Through Road" signs must be displayed atthe open end(s) of the road.

End of block closures could be made simply bythe use of "No Entry" signs, but these mayprove to be ineffective, particularly if driversapproaching a closure can see traffic movingbeyond it. Hence it is preferable to provide aphysicai barrier to prevent drivers violating therestriction. This may be in the form of a trafficisland with a sign showing the direction thatvehicles must now follow. It is important toensure that the arrangement is in keeping withthe area and consideration should be given tothe provision of landscaping.

Where a closure is made at a mid-blockposition, provision must be made for largevehicles, such as refuse vehicles to turnaround.

Typical turning heads are shown in Figure 5.13.The choice of layout is dependant on the width

Page 5/27


of carriageway available and the positions ofexisting property accesses that have to beaccommodated by the ciosure.

Any barriers or turning heads shall be designedin such a way as to ensure that emergencyvehicles are able to gain access. This isachievable by the use of lockable barrier gatesor demountable bollards. Whichever is chosen,it must be capable of preventing private vehiclesfrom passing through the restriction. For thisreason, solutions such as a route through alandscaped area are not recommended as theyare open to abuse, particularly by drivers of fourwheel drive vehicles.

Whatever the designed restriction, adequateaccess and parking shall be provided forresidents.

Partial closure allows access into areas.However, by the use of width restriction orraised road humps it is made unattractive forgeneral road users.

Partial closure is often incorporated atundesirable locations along the major road todiscourage use such as at accesses near tomajor junctions. Where the minor road has toremain open due to emergency vehicle accessrequirements or limited access routes into thedevelopment then partial closure is an easy wayto control general use.

January 1997

SECTIONS

Page 5/28

•

•


I·22 -I

,","24.5

.1"118.5

~:[;"

'" //2;a::I() 1>6'~ ':qO:/

H.-f-

~6'~Q II

II

~I

16

All dimension in metres

Note:A central island radius of 10 metres willjust allow the vehicle to turn about. Inview of the restricted area available, theisland may be reduced or omitted altogether.

Minimum Dimensions for Turning HeadsIn situations where larger vehicles have to beaccommodated, these dimensions should be increased totake account of the larger turning radius and sweptpath area.

Figure 5.13 Typical Turning Head Details



5.19 LANDSCAPING

Apart from the amenity benefits, the landscapetreatment of medians, junctions and verges canhave practical advantages. By groundmodelling, perhaps in conjunction with planting,the layout of the road can be made moreobvious to traffic.

Landscaping can play an important part in aidingdrivers waiting to exit the minor road byproviding reference points or features by whichto judge the speed of drivers approaching on themajor road. This is particularly useful where amajor/minor junction is located In an openlandscape, where there Is a lack of naturalreference points. Planting can also provide apositive background to the road signs aroundthe junction, whilst visually uniting the variouscomponent parts. it is important that a widerview does not distract from the developing trafficsituation as the driver sees it.

Specialised planting, which might be moreappropriate in an urban area, generally requiresgreater maintenance effort if it is to besuccessful. The preferred maintenance methodIs an automatic Irrigation system connected to areturn effluent main. Approval for any suchscheme must be sought from the Director of theCivil Engineering Department and the DrainageDivision. If a return effluent main is unavailable,care should be taken so that watering does notrequire tankers to obstruct trafficked lanes atany time.

A well defined maintenance programme shouldbe developed if extensive planting is used toensure that such planting does not obscureeither opposing traffic or traffic signs at any time.

In rural areas, planting should be restricted toindigenous species and be related to thesurrounding landscape. In the desert, forexample, any planting of other than localspecies would appear incongruous andlandscape treatment would normally berestricted to ground modelling.

SECTION 5

the opposite side of the roundabout to the pointof entry can, without restricting necessaryvisibility, avoid distraction and confusioncaused by traffic movements of no concern toa driver. Planting can provide a positivebackground to chevron signs and directionsigns on the central island while visually unitingthe various vertical features and reducing anyappearance of clutter.

Generally the planting of roundabout centralislands less than 10m in diameter isinappropriate as the need to provide drivervisibility leaves only a small central areaavailable. Such a restricted area of planting isout of scale with the roundabout as a whole,and becomes an incongruous "blob".

Recent experiments with a ring of black andwhite paving laid in a chevron pattern inside thecentral island perimeter at a gentle slope haveproved successful in improving the consplcuityof central islands and they can be effectivefrom a safety point of view (Figure 5.14).

It is common to construct features such ascoffee pots etc. in roundabouts. They becomea focus for the traveller, and if designed andpositioned correctly will prove an asset to thesurroundings.

Lighting of central islands or any landscapefeature is important, though care should betaken to avoid distraction or dazzle to drivers.

At roundabouts, the areas required for visibilityenvelopes can be planted with species having alow mature height, with higher and denserspecies of bushes and trees towards the centreof the island. Due allowance for the situationthat will develop with matured growth must bemade.

Apart from the amenity benefits, the landscapetreatment of roundabouts can have practicaladvantages. By earth modelling, perhaps inconjunction with planting, the presence of theroundabout can be made more obvious toapproaching traffic. The screening of traffic on

January 1997

Figure 5.14

Section x-x

Contrasting Chevron Markingsfor Roundabouts

Page 5/30


SECTION 6 JUNCTIONS

6.1 GENERAL

The scope of this section of the QHDM is toidentify the main types of major/minor junctionwhich can be used in the design of new and theimprovement of existing roads.

SECTION 6

however, important to ensure that the minorroad traffic movements are still adequatelyprovided for. Spacing between consecutivejunctions is best considered in terms of theminimum distance that allows traffic travellingon the main road and traffic leaving it or joiningit, to do so in an easy, efficient and safemanner.

Advice is given on the main factors which affectthe choice between different types ofmajor/minor junction, on the siting of suchjunctions and suitable types of layout.

In determining this distance, due considerationmust be given to:

• Design speeds

• Traffic on the mainline

• Traffic leaving the main road to thesecond junction.

• Traffic entering the mainline from the firstjunction

• Provisions for turning traffic wishing tocross, join or leave at the junction.

Horizontal and vertical geometry of themain road for visibility

Weaving lengths for merging/divergingtraffic flows

•

•

Consideration should also be given to thespacing of the deceleration lanes and theacceleration lanes of junctions along the maincarriageway. Refer to Clause 6.14 forinformation on diverge/merge distances. Thespacing of these junctions should relate to theweaving characteristics of:

The minimum spacing between consecutivesimple T-junctions on access roads and serviceroads is 80m, and across a staggered Tjunction 40m. Refer to Clause 6.7.15 foradditional information on stagger distance andrefer to Clause 7.4.9 for additional informationon weaving sections.

Junctions are widely recognised as one of theprimary locations of accidents on all roads.Safety is therefore of paramount importanceduring the development of any junction design.A number of safety issues such as: visibility;driver perception; signing and road markings;traffic control and pedestrian access, need tobe considered as part of the designdevelopment process. More detailed guidanceon these and other relevant factors is givenelsewhere in this section.

6.1.1 Junction Spacing

The frequency at which junctions are located ona main road is usually a function of thesurrounding area and its current or futuredevelopment, i.e. rural or urban environment. Ingeneral terms, urban environments arecharacterised by a mixture of residentialproperties, and commercial and industrialdevelopments/outlets. There is usually a highdemand for through traffic and local trafficmovements. Consequently there is a highdemand for access across, onto and off of themain road from the local road network.

To ensure a consistent approach to the designof the major/minor junctions, a series ofrecommendations covering the geometricdesign of the key elements of the junction, andhow these can be best combined to produce agood overall design, have also been included.

In contrast, rural environments generally havefew residential properties that are interspersedintermittently with industrial and commercialdevelopments/outlets. The demand on the mainroad is for through traffic with local trafficmovements catered for chiefly by the local roadnetwork. As demand for links with the main roadare lower than urban environments, junctionsoccur much less frequently.

When improving existing roads it may benecessary to reduce the number of junctions onthe route. This may be achieved by:

• Provision of service roads to collectminor roads

• Closure of minor roads and provision ofturning heads, refer to Section 5.

The spacing of junctions, particularly in urbansituations is critical to ensure that disruption totraffic on the main road is minimised. It is



6.1.2 Traffic Flows

An important factor that governs the choice ofjunction type at a given location is the volume oftraffic that is currently using the main road andside roads, and the predicted future trafficdemand. Before any detailed evaluation can bemade It is important to obtain the best estimateof all the relevant traffic flows and turningmovements for the junction.

SECTION 6

corner radii and lane widths that are likely to beaffected. Swept paths should be checked usingstandard templates or a computer softwarepackage.

The vehicle classification to be used in Qatar isshown in Table 6.1.

Failure to make adequate provision is likely toresult In:

In situations where this data is not readilyavailable it will be necessary to undertake trafficsurveys, or use traffic modelling to predict thelikely traffic flow levels.

• A reduction in the junction capacity asthe larger vehicles are forced to straddletwo traffic lanes to facilitate the turningmovement at the junction

The composition and turning movements oftraffic will influence the geometric layoutadopted. A high proportion of heavy goodsvehicles for example will dictate the minimumlane width and corner radii to be adopted at thejunction. A high proportion of turning traffic mayrequire the provision of a segregated ordedicated turning lane at the junction, to ensurethat adequate through traffic capacity is

••.• l1l.aintained.

Predicted future traffic flows are importantbecause they:

• Enable the design to be tailored toprovide sufficient capacity to meet thefuture traffic flow demands

• Overrunning of kerbs

• Reduced visibility for other trafficapproaching or negotiating the junction.

These design principles should be extended tothe positioning of street furniture such as signs,splitter islands, traffic signals and lightingcolumns.

Allowance shall be made for the swept turningpaths of long vehicles where they canreasonably be expected to use a junction.Consideration shall also be given to themanoeuvring characteristics of these vehicles inthe design of staggered junctions.

•

Guidance on acceptable traffic flows for junctiontypes and layouts are given throughout thisSection.

•

•

Enable a decision to be made toconstrain the traffic flows at the givenlocation for a particular reason

Identify the need to allow for current orfuture junctions.

All of the geometric parameters given in thissection for use in the design of a major/minorjunction have been developed to cater for a16.5m long artiGulated vehicle, whose turningwidth is greater than for most other vehicles thatregUlarly use these junctions.

The turning requirement of a 20.0m longdrawbar trailer combination are less onerousregarding road width.

6.1.3 Design Vehicles

An obvious but often overlooked aspect of thedesign of junctions is the type of vehicle that willbe using the junction. Different sizes andclasses of vehicle have varying swept pathsand turning circles. All junctions need to bedesigned to allow the vehicle with the greatestswept path, that will regularly use the junction toturn in a safe and easy manner. For example a36 tonne articulated lorry is unlikely to be aregular user of a residential road. In thisexampie the most likely largest vehicle wouldbe a refuse vehicle or a school bus. Generally,the design vehicle is likely to be a heavy goods,public service, or refuse vehicle and it is the

January 1997

In cases where hardstrips are present, thedesign vehicle is assumed to use these onsome turns, and at some simple junctions, itmay encroach into opposing traffic lanes.

Where buses or other long rigid vehicles form asignificant portion of total or peak time traffic,and their turning movements within thesedimensions would be awkward or present ahazard or significant delay. Then corner radiiand lane widths should be increased based onthe use of appropriate swept path templates.

Page 6/2


6.1.4 Siting of Junctions

The siting of junctions for new build andimprovement schemes is very important.Failure to choose a suitable location can reducethe effective operation and safety of thejunction. It is essential to include engineeringconsiderations in the early pianning stages tohelp minimise poor land use.

Sites that should be avoided include:

• Where the major road is on a sharpcurve and visibility may be impaired bywaiting vehicles

SECTION 6

• Where the minor road approaches areskewed less than 70° or greater than110° to the main road.

• • At the top or bottom of gradients greaterthan 4% on the main road

• Where the minor road approaches themain road on an up or down gradientgreater than 2%

• Where junction frequency is excessive.

The problems listed above while not exhaustivecover the more commonly occurring situations,and they can usually be overcome bymodifications to the horizontal and verticalalignments.

In situations where, because of site constraints,it is not practical to fully apply these principles,then a compromise will need to be establishedthat minimises the potential risks to driversapproaching the junction. Measures such asreduced speed limits, alignment constraints,additionai signing and road markings can helpto minimise the potential hazards to the driver.


Vehicle Dimensions frurning Width Average Whaelsetwun kerb No. at No. of (on lHIch sideVehicle Type Class

1180") Axles StondordWeight (kg)

at the vehicle)length fm} Width{m) Height (m) 1m) Axles

~ cPr1BOD 4.5 1.7 1.5

~ 1 2500 5 1.9 2 5 2 - 1-10 2600 5 1.9 2;; Saloon cet 4w~drjyB Pick-up van·•()~ 2 1800 4.5 1.7 1.5 5 2 - 1-1

Taxi

·~1-1

• , 5900 7 2 2.6 15 2 0.2-0.5 "~

0"2•0 IAini-ous

~~

([l@OO~,m

4 16500 12 2.5 , 24 2 1.3-5.0 1-2

Bus/coach.~

0

QI ~0 1-1as

§:2 5 7500 8.5 2.5 3.2 15 2 0.5-7.0 "- . ~ G 1-2~ >I:; Pick-up lorry

QBII Q ©Ii6 1BOOO 12 2.6 4.1 24 2 0.5-7.0 1-2

·• 2 Axle lorry-rigid<;:E· Q>

CJUPW·~0 7 24000 12 2.6 4.1 24 3 1.5-4.0 1+2+20 @=@'a~

> 3 Axle lorry-rigid••J:

~ 8 SDDDD 16.5 2.6 4.1 16 3 0.6-10.0 1"'2+2

3 Axle-articulated

Refer Tabla 9.1 for Average No. 01 Standard Axles Por Vehicle

c.. -jIII III::l 0-C illIII.., (J)

'< :......CD

!!ll <'"::rc5"ill()iii"CJ>CJ>=;;o·~0·Ol

(j)::r'"~~

S..!.'S

"1JIII

(Q1Il

~

.. • •

o

~jJ

::I:15::I:

~Cm(fl

15zs:»zc:»r-

(flm~5z0>

• •c.. -;III '"::l 0-c: roIII~ 0)

'< :...~

(Q

~I <CD:r0'ro()iii"<J)<J)=;;0'!'l.o'::l

Cil:rCDm.'"sa.B

-cIII

lQCO

lJi

Vahic!s Dlmltnsions Turning Width AvarageWheals

etween kerb No. at No. orVlJhicle Type Class (1 Bo·) Axles Standard (on B8Ch lOide

~9lght (kg) Length fm) Width(rnj Height fm} em) AXles of lha vahlcla)

~ , 36000 16.5 2.6 4.1 16 4 1.5-7.0 1+2+22

4 AXle-articulated

~ 1D 43500 16.5 2.6 4.1 16 5 2.5~7 .0 1+2+222

~ 5 Axht-artlculated

QIIWIJill 11 36000 16.5 2.6 4.1 16 4 1.5-7.0 1+22+2

•• 4 Axle-articulated'0:c•>

111111 1111111111 I111·~ 12 42000 16.5 2.6 4.1 16 5 2.0-7.0 1+22+220~

~ ~ ~~

>• 5 Axis-articulated•J:

IIIIIIII~ [[]I]]( 13 49500 16.5 2.6 4.1 16 6 1.5-7.0 1+22+222

~ l;li6 Axle-articulated

~ 14 SODDD 9 2.6 4.1 2D 3 2.0-7.0 +2+22

3 Axle-trailer

~ 15 36000 9 2.6 4.1 2D 4 2.0-10.0 +22+22

4 Axlll-traiJ9r

~ 16 1000 2.3 D.61.B (INCL - - - -

M Dtor~bjcyclerider)

Refer Table 9.1 ror Average No. of Standard Axles Per Vehicle

o

~:c:ri5:r

~cmC1li5zs:»zc»r-

C1lm~oz'"


6.2 TYPES OF JUNCTION

There are seven basic types of junctions thatshould be considered for use.

There are advantages and disadvantages toeach of the seven types and the engineershould carefully consider the suitability of eachtype for the intended location and purpose.

The seven basic junction types are as follows:

6.2.1 T-Junction

The T-Junction, of which there are five mainvariants, is an at-grade junction of two roadswhere the minor road terminates at the majorroad at right angles. It is the most common typeof approach road junction and is a suitablesolution for coping with most traffic flowrequirements. Traffic control is generallyprovided by "Give Way" or "Stop" signs/roadmarkings on the minor approach but couldinclude traffic control on all approaches.

In certain urban situations where traffic,pedestrian or safety requirements dictate,signalization may be required. The type oftraffic control is determined through a "warrantanalysis" (refer to the Qatar Traffic Manual).

6.2.2 Simple Crossroads

The crossroad is an at-grade junction of tworoads that cross approximately at right angles.Simple crossroads are not safe junctionsbecause of the high number of traffic movementconflicts that can occur at the same location.For this reason, the use of crossroads is notrecommended. A safer solution, locationpermitting, is to provide a roundabout or signalcontrol.

6.2.3 Staggered Junction

A staggered junction is an at-grade junction ofthree roads, where the major road is continuousthrough the junction. The minor roads intersectthe major road forming two separated Tjunctions on opposing sides of the main road.

This type of junction is the preferred alternativeto a simple crossroad. However, should futuretraffic volumes be expected to increase, then aroundabout or signalisation may be preferablefrom the outset at certain locations.

January 1997

SECTION 6

6.2.4 Skew or Y-Junction

This type of junction is an at-grade junction oftwo roads, where the minor road approachesthe major road at an oblique angle. In a similarmanner to the T- junction, traffic control isproVided by "Give Way" or "Stop" iine roadmarkings in conjunction with "Stop" or "GiveWay" signing on the minor road.

As skew angle to the main road decreases, thejunction becomes less safe.

6.2.5 Roundabouts

A roundabout is a special form of at-gradejunction characterised by a one-way circulatorycarriageway around a central island located atthe intersection of a maximum of six roads.Traffic flows around the central island on thecirculatory carriageway in an anti-clockwisedirection until it reaches the required exit point.Entry onto the roundabout from the approachroads is controlled by the appearance of gaps inthe circulating traffic flow. Traffic wishing toenter the roundabout must give way to trafficalready on the circulatory carriageway.

6.2.6 Grade Separated Interchange

This type of junction removes the principlevehicle conflict by the provision of gradeseparation between some of the turningmovements. These junctions are complex andinclude extensive connecting roads and loops.Grade Separated Interchanges are discussed inSection 7 of this manual.

6.2.7 Traffic Signals

Whilst not strictly a junction type, traffic signalsmay be implemented on a number of junctiontypes to control the movement of traffic.Junctions may be specifically designed forsignal control or signai control may be added alater stage.

The design of physical features of this type ofjunction, excluding the signal design, arecovered within this manual. An introduction tosignaiized junctions is given in Clause 6.16.

Page 6/6


6.3 JUNCTION SELECTION

The selection of a junction type at a givenlocation is important for operational, economicand safety reasons.

The engineer should carefully select thejunction type for the location in accordance withthe considerations listed below.

However, in some circumstances, localconditions such as driver behaviour may alsoinfluence the engineers choice of junction typefor a particular location. Where it is felt thatdrivers may ignore "Stop" or "Give Way" signs,a different or higher type of junction could beselected.

Apart from the basic selection considerationsgiven below, the engineer should also considerthe possibility of planning benefits to be gainedby the selection of junction types at locationsthat promote the use of the roads in thehierarchy defined in this manual.

The following points should be considered:

6.3.1 Status of Intersecting Roads

Restrictions are placed on the categories ofroad that may meet. As a result, for any givenpermitted combination of road types, onlycertain junction types will be appropriate foruse. Table 6.2 below outlines acceptablecarriageway and junction combinations.

SECTION 6

6.3.2 Continuity of Standard

In the interests of safety, the sequences ofjunctions on a section of road or neighbouringroads of similar standard shouid not involvemany different layout types. A length of majorroad comprising roundabouts, single lanedual ling, ghost islands and simple priorityjunctions would inevitably create confusion anduncertainty for drivers, and may result inaccidents. The safest schemes are usuallystraightforward, containing no surprises for thedriver.

6.3.3 Junction Capacity

The form that a junction takes is greatlyinfluenced by the volume of traffic predicted topass through it. All junction layouts will need tobe analysed to ensure they have sufficientcapacity. This analysis should be carried outusing a standard software package (eg.ARCADY for roundabouts and PICADY formajor/minor junctions).

Junction selection by capacity is given in Figure6.1. It is based on capacity and on UKcongestion acceptance levels. Engineers mayconsider that higher standard facilities shouldbe provided than that indicated by thenomograph for operational or safety reasons.

The detailed geometry of junction types relatingto capacity is given in Clause 6.7.

Minor

7.3m Carriageway 11.3m Carriageway Ouol-2 Oual-3

Major Rural Urban Rural Urban Rural Urban Rural Urban

7.3m Rural T,R, .

Carriage-way Urban T,Ts.R T,Ts,R

11.3m RuralCarriage-

way Urban I· T,Ts,R "'. T,Ts,R

Oual-2 Rural T,Tu,R,1 R,I

Urban T,Ts,V,R,1 T,Ts,V,R,1 Ts, R,I

Duat-3 Aural T,Tu,R,1 R,I R,I

Urban T,Ts,V,R,1 T,Ts,V,R,1 Ts, R,I Ts, R,I

Key:T T-JunclionTs T-Junction with Signals

RTu

RoundaboutT-Junction with U-Turn

IV

InterchangeService Road

Table 6.2 Possible Junction Types for Different Major Road Carriageway Configurations



oN

o

SECTION 6

o....

o<0

o<0

>:'"0 ~..,. 0

~....a«:

"- «:0~

x;;:

0 a..J

"" U.

a«:00::0::0--,«:::;;

0N

+ •++ +

+ ++

0

(.IeM-oMll .LOW ,O~ x MOlo 0\10<1 <lONIl'l

Figure 6.1 Junction Selection By Capacity



Vehicular and pedestrian accidents mainlyoccur at major/minor junctions. More accidentsoccur in the urban environment than the rural.

This section gives advice and standards for thegeometric design of major/minor junctions withregard to traffic operation and safety.

•6.4 MAJOR/MINOR

GENERAL

6.5 SAFETY ATJUNCTIONS

JUNCTIONS

MAJOR/MINOR

SECTION 6

6.6 MAJOR/MINOR JUNCTION TYPES

6.6.1 The Simple T·Junction

IIIIIIII

~ I______-._~======J ~ _

•

These accidents are mainly associated withpoorly judged left turn movem~nts onto andfrom the major road and with incautiousovertaking manoeuvres.

Various methods to enhance safety can beintroduced at major/minor junctions. Theengineer should review each junction on anindividual basis.

Ghost Islands and single lane dualiing (physicalislands) to shelter left turning traffic anddiscourage overtaking are discussed in Sections6.6 and 6.7. Other safety measures that couldbe adopted are as follows:

• The use of road markings, double whitelines, raised rib markings, narrow centralhatching, block paving, ceramic studs,refuge islands with keep right bollards ordifferent coloured surfacing to discourageovertaking manoeuvres on the majorroad

• Skid resistant road surfaces

Figure 6.2 Simple T-Junction

A simple T-Junction is without any ghost orphysical islands in the major road, and withoutchannelizing islands in the minor roadapproach. Refer to Figure 6.2.

Simple T-Junctions are appropriate for mostminor junctions on single carriageway roads, butnot dual carriageways. For new rurai junctions,they shall only be used when the design flow onthe minor road does not exceed 300 vehiclesAADT (two-way) and on the major road doesnot exceed 13000 vehicles AADT (two-way).

At existing rural and urban junctions upgradingto a left turning facility, ghost Island or singlelane dualling should be considered when safetyconsiderations dictate or where the minor roadflow exceeds 500 vehicles AADT (two-way).

•

•

At urban locations where pedestrianmovements occur, pedestrian barriers,central refuge islands and at somelocations, pedestrian crossings andcontrolled pedestrian crossings

At some locations where safety is anissue, the major/minor junction mayrequire traffic signals.

6.6.2 T-Junction with Ghost Island

AT-Junction with widening on the major road toaccommodate a ghost island and an extracentral lane for turning traffic. The minor roadapproach should also have a channelizingisland to direct vehicles to the correct positionfor turning movements. Refer to Figure 6.3.

In addition, in rural areas, problems occur withdriver perception of the termination of the minorroad. Drivers at night, on unlit rural roads aremostly involved with this type of misjudgment.The engineer shall ensure that there are nophysical obstructions to the path of such avehicle.

January 1997

Ghost islands will enhance safety of the junctionby giving shelter to left turning traffic fromopposing vehicles and vehicles approachingfrom behind. Measures to discourageovertaking at ghost island widening could be theuse of physical traffic islands, double whitelines, different coloured surfacing and ceramicstuds.

Page 6/9


Figure 6.3 T-Junction with Ghost Island

J

Figure 6.4 T-Junction with Singie Lane Dualling/Physical Island

•

There may be certain conditions when singlelane dualling could be misinterpreted by drivers:

the major route to speed up through the junctionwhere slow vehicles may be crossing. Careneeds to be taken when siting the junction.

The single lane dual ling carriageway width is6m, where 4m is the running carriageway andthere are 1m hard strips on both sides. Somedrivers may try to overtake in this width andhatching of the 1m strips will discourage suchmanoeuvres.

Ghost islands, however, should not bepositioned where overtaking opportunity isrestricted either side of the junction becausedrivers may use the wide ghost island hatchingand central lane as a place to overtake. If aghost island has to be positioned at theselocations then an alternative such as single ianedualling should be considered.

Ghost island junctions should not be usedwhere traffic turning ieft out of the minor roadneeds to make the manoeuvre in two stages.This can occur when the major road flowexceeds 18000 AADT (two-way).

6.6.3 T-Junction with Single Lane Dualling• Where a length of road contains

alternating single and dual carriagewaysections

Single lane dualling (physical islands) can beused on rural single carriageway roads toshelter left turning traffic on the major road andprevent overtaking. It can also J;le used wherethe traffic turning left out of the minor roadneeds to make the manoeuvre in two stages.Refer to Figure 6.4.

Single lane dualling does, however, bring inother safety issues. With the improved highwaylayout there may be a tendency for drivers on

January 1997

• Where single lane dualling is proposedwithin 3 kilometres from the end of a longlength of dual carriageway.

In these cases, other forms of junctions shouldbe considered.

Page 6/10


I

====--~-----------------------------

~::=::: - -----j§JI-So1-

"

SECTION 6

------------------

Figure 6.5 T-Junction with Dual Carriageway with Median Opening (Signaiized Only)

Figure 6.6 T-Junction on a Dual Carriageway with Carriageway Separation

6.6.4 T·Junction on a Dual Carriageway withMedian Opening (Signalized)

These T-Junctions may be used on two or threelane dual carriageways. This layout shall onlybe implemented with traffic signals. Refer toFigure 6.5.

Short lengths of dual carriageway just toincorporate a junction should not be provided.

On continuous dual carriageways the medianwidth is usually between 2 and 8m. If required,this width can be widened to provide space fora left turn lane and waiting space for vehiclesturning left into the minor road.

6.6.5 T·Junction on a Dual Carriageway withCarriageway Separation

On dual carriageways, the left turn manoeuvrefrom the minor road is prevented by the median,unless the minor road warrants signalization to

January 1997

be incorporated. The turning facilities should beprovided nearby at another junction. Thenearby junction may be grade separated, aroundabout, signalization or a U-Turn wheretraffic speed and traffic flow conditions aredifferent. Refer to Figure 6.6. Acceleration anddeceleration lanes from and to the minor roadshould be designed in accordance with throughtraffic volumes and speeds.

6.6.6 Crossroads

As discussed earlier in Clause 6.2.2, simplecrossroads are not recommended. Staggeredjunctions are always considered a much saferalternative, especially if a significant proportionof the flow on the minor roads is crossmovement. In residential areas, considerationshould be given to closing off one of the arms ofthe crossroads to create a preferred simple TJunction.

Page 6/11


6.6.7 Staggered Junction

A staggered junction comprises a major roadpassing through the junction with opposed TJunctions on either side. Figu'res 6.7 to 6.11show variations of staggered junction layouts.

Left/Right StaggerThe left/right stagger is preferred because thetwo left turning traffic streams on the major road

SECTION 6

do not overlap, and the left turning traffic fromthe minor roads does not mix with the turningtraffic on the major road. Refer to Figure 6.7.

Right/Left StaggerA simple right/left staggered junction should notbe considered. However, the right/leftstaggered junction with ghost isiand or singlelane dualling would be an alternative. Refer toFigures 6.10 and 6.11.

~ .. '''''''--I VI

II

I

Figure 6.7 Simple Left/Right Staggered Junction

Figure 6.8 Left/Right Staggered Junction with Ghost Island

Figure 6.9 Left/Right Staggered Junction with Single Lane Dualling



A

SECTION 6

..Figure 6.10 RighVLeft Staggered Junction with Ghost Island

Figure 6.11 RighVLeft Staggered Junction with Single Lane Dualiing

6.6.8 Right and Left Hand Skew Junction

Figure 6.12 shows a left hand skew junctionwith a ghost island. The junction couid also beright handed.

......".

\.,-----'"'._....!..U_.~ .._:::::::::::::::::::::::::::~:::&~~~~

Figure 6.12 Left Hand Skew Junction

January 1997

This form of junction can be a solution when anexisting minor road joins the major road at askew angle. It is sometimes calied a YJunction.

The existing junction is improved on safetygrounds by channelizing the minor road withislands and road markings, and connecting it tothe major road at right angles for optimumvisibility.

Typicaliy skew angles of 70' or greater do notrequire straightening to approach the main roadat 90'. As skew angles become smalier a largearea is required in order to achieve an effective90' junction.

Other combinations of skew junctions couldcombine staggered junctions, single lanedualiing and dual carriageways.

Page 6/13


6.7.2 Design Speed

This section outlines the geometric designelements to be considered in the design ofmajor/minor junctions. Many of the elementsare dealt with separateiy, and the engineershould work systematically through the designprocedure prior to assembling the componentparts. This is an iterative process, and it maybe necessary to alter part of the junction designcovered previousiy in order to achieve asatisfactory design.

6.7 MAJOR/MINORELEMENTS

6.7.1 General

JUNCTION

SECTION 6

Drivers approaching a major/minor junctionfrom both the major road and the minor roadshall have unobstructed visibility in accordancewith the following clauses. The envelope ofvisibility for driver's eye height is as described inSection 2.

Major RoadDrivers approaching a major/minor junctionalong the major road approaches shall be ableto see the minor road entry from a distancecorresponding to 1.5 times the stopping sightdistance (SSD) for the design speed of themajor road as described in Section 2. Thisintervisibility allows drivers on the major road tobe aware of traffic entering from the minor roadin time for them to be abie to slow down andstop safely if necessary.

•

When considering geometric standards for thedesign speed of the major/minor road junctions,it is the design speed of the major road thatgoverns.

6.7.3 Visibility

Clear visibility on the approach to, at andtravelling through a junction is essential for thesafe and efficient use of that junction.

In determining the correct visibilityrequirements for a junction, the engineer mustconsider both the layout of the junction and thevehicles that will use it. The visibility andintervisibilily requirements provided within thisclause are related to the design speed of themajor road and little benefit is to be gained byincreasing them. However, each junction mustbe considered on a site-specific basis with anassessment made of additional visibility to beprovided due to factors such as:

• Width of major road to be crossed

• Traffic control on the minor approachroad

• Turning movements to be made at thejunction

• Gradient of the approaches anddepartures

• Type of vehicle that will be using thejunction, ego large, slow speed vehiclesrequire additional Visibility.

As well as having adverse safety implications,poor visibility reduces the capacity of turningmovernents.

January 1997

The concept of adequate visibility to make safeturning movements also applies to vehiciesturning ieft into the minor road from the majorroad.

Minor RoadMinor road traffic has to approach the junctionand join or cross the major road when there aregaps in the major road traffic streams. It istherefore essential that minor road drivers haveadequate visibility in each direction to see thejunction layout and oncoming major road trafficin sufficient time to permit them to make theirmanoeuvres safely.

The principle of prOViding the reqUired visibilityfor drivers approaching the junction from theminor road has three distinct features (refer toFigure 6.13):

W: Approaching drivers should haveunobstructed visibility of the junction from adistance corresponding to the stopping sightdistance (SSD) for the design speed of theminor road. This allows drivers time to slowdown safely at the junction, or stop, if this isnecessary. Where a "Give Way" or "Stop" signis proposed, the visibility envelope shall bewidened to include the sign.

z: A driver approaching the junction shouldbe able to see clearly the junction form andthose peripheral elements of the junction layout.This provides the driver with an idea of thejunction form, possible movernents andconflicts, and possible required action beforereaching the major road. This point is called the'z' point which is 15m back aiong the centrelineof the minor road measured from thecontinuation of the line of the nearside edge ofthe running carriageway of the major road (notfrom the continuation of the back of the majorroad hardstrip, if this is present).

Page 6/14

•

..

•


X, Y: The distance back along the minor roadfrom which the full visibility is measured isknown as the 'x' distance. It is measured backalong the centreline of the minor road from thecontinuation of the line of the nearside edge ofthe running carriageway of the major road. The'x' distance shall be desirably 10m.

From this point an approaching driver shall beable to see clearly points t9 the left and right onthe nearer edge of the major road runningcarriageway at a distance given in Table 6.3,measured from its intersection with thecentreline of the minor road. This is called the'y' distance. Relaxations are not available forthis distance.

If the line of vision lies partially within the majorroad carriageway, it shall be made tangential tothe nearer edge of the major road runningcarriageway, as shown in Figure 6.14.

In difficult circumstances, the 'x' distance maybe taken as a relaxation from 10m to 7.5m forlightly trafficked simple junctions, and inexceptionally difficult circumstances, to 5.0mback from the nearer edge of the major roadrunning carriageway. In some urban locationswhere only light vehicles are involved, the 'x'distance can be further reduced to 2.5m.

SECTION 6

The 'x' distance, from which full 'y' distancevisibility is provided, should preferably be notmore than 10m as this induces high minor roadapproach speeds into the junction, and leads toexcessive iandtake.

Similarly, although the 'y' distance shouldalways be provided, there is little advantage inincreasing it, as this too can induce highapproach speeds and take the attention of theminor road driver away from the immediatejunction conditions. Increased visibility shouldnot be provided to increase the capacities ofvarious turning movements.

These Visibility standards apply to new junctionsand to improvements to existing junctions.

If the major road is one way, a single visibilitysplay in the direction of approaching traffic willsuffice. If the minor road serves as a one-wayexit from the major road, no visibility splays willbe required, provided that forward visibility forturning vehicles is adequate.

Vehicles parked within splay lines will obstructvisibility. Parking and access should bedesigned to prevent this. Care should also betaken in the placing of signs, landscaping andstreet furniture within the Visibility splay areas toensure that their obstructive effect is minimised

Design Speed 'y' Distance Minimum 'x'of Major Road (m) Distance

(kph) (m)

140 350 10120 295 10100 215 1080 160 1070 120 7.560 90 7.550 70 5.0

< 50 50 2.5. . ..Note. In all cases the preferred x distance Is 10m. The mInimum x distances given shall only be used In difficult CIrcumstances, In accordancewilh Clause 6.7.3.

Table 6.3 Minimum 'x' and 'y' Visibility Distances from the Minor Road


I

Iy

'1

y

" Lines over which unobstructedvisibility shouid be provided

-----------1------- -_.--

I........

~, - - - -1 = = ='= = = """x t..:- v-:--"-. ---. ., ' I . ..-, ' ..-,

I..- z = 15 m, ..-, ..-

"·1/ ', ,w

I. I . x 'x' Distance. .

'VI Distance

\'y

.. w Minimum Stopping Distance (SSD)

i for Approach Road Design Speed

II


•

•

Figure 6.13 Visibility Standards

-- ---..-:::::::::"'.......,,,----- -

y

Tangent edge of carriageway

x 'x' Distancey ty'Distance

Figure 6.14 Visibility Standards with a Curved Major Road



1.22m

,,,,,l:k: ~t.OE ,3~ ,';0,,

B"'

27mR--- ----__ 1B"9mR ----- I~EE, '"4 ~

---.::i=±::;;O_d':-~"

~

For simple junctions, where no provision is tobe made for large goods vehicles or buses, it isrecommended that the minimum circular cornerradius should be 6rn in urban areas and 10m inrural areas. Where provision is to be made forlarge goods vehicles or buses, therecommended circular corner radius Is shownin Table 6.4 and Figure 6.15.

6.7.4 Corner Radii

These radii only apply where there are nodiverge tapers or lanes, or merge tapers. Referto Sections 6.7.13 and 6.7.14.

Alternatively, where large goods vehiclescomprise a significant proportion of the turningmovements, use of the compound curve shownin Figure 6.16 is recommended.

Junction Taper Length of CornerType Rate Taper (m) Radius (m)

T L R

UrbanSimple

Junction 1:5 30 10

RuralSimple

Junction 1:10 25 15

GhostIsland

Junction 1:6 30 15

StaggeredJunction 1:8 32 15

All Other . . 20

Figure 6.16 Design of a Compound Curve

6.7.5 Carriageway Widths

All of the geometric parameters defined in thisclause can be seen for the three main types ofmajor/minor junctions in Figures 6.17 - 6.19.

Through LanesAt ghost and physical island junctions, thethrough lane in each direction shall be 3.65mwide, exclusive of edgestrips.

At dual carriageway junctions, the through lanewidths remote from the junction shall becontinued through the junction.

Table 6.4 Circular Corner Radii

R = Corner RadiusL = Length of TaperT = Taper Rate

Minor Road ApproachesOn a minor road approach of nominal width7.3m, where a channelizing island is provided,both lanes shall be 4.0m wide at the point wherethe hatched markings surrounding thechannelizing island begin. (Refer to Figure6.17).

L I

J

At the point where the channelizing islandcommences, the widths on either side shall beas follows:

a) On the approach to the major road, 4.0mwide for a ghost island or 4.5m wide forsingle lane dualling or a dualcarriageway, exclusive of hardstrips. Ifthe approach on the minor road consistsof two lanes, this dimension shall be5.5m.

Figure 6.15 Circular Corner Radii b) On the exit from the major road, 4.5mwide for a ghost island, or 5.0m wide forsingle lane dualling or a dualcarriageway, exclusive of hardstrlps.



If there are no channelizing islands in the minorroad, the nominal approach width shouldcontinue up until the tangent point of the curveto join the edge of the major road runningcarriageway.

•. 7.3m Nominal Widthb. 4.0m In All Cunc. 4.5m for Gholll.land

5.0m for Slngll Lan, Qualllngtlr Dual Carrlaglway

--------~- ====

d. 4.0m f"rGhnllsland4.5m ForSlngl. Lan, OU.Hlnllor Du,l Cam_lIlwlY5.5m It Two lana Approach

-- - - --""'---

SECTION 6

Where the minor road approach is a dualcarriageway it should be either reduced to asingle carriageway before the junction (seeFigure 6.18), or signalized.

Where 16.5m long articulated vehicles (eg.Class 8) are anticipated, but are likely to formonly a very small percentage of the total numberof vehicles and where conflicts will not occur onbends, the carriageway widths should bedesigned to cater for the lower class vehicle thatwill regularly use the junction with an additional1m allowance for variation in vehicle position.Alternatively, figures from Table 6.5 could beused.

An articulated car transporter will turn in thewidths shown, but where provision is to bemade for this type of vehicle, street furnitureabove 2.5m high should be set back at least 1mfrom the edge of the minor road carriageway atthe bellmouth (this does not apply forchannelizing islands) to allow for the projectionof the trailer over the tractor cab.

•

Figure 6.17 Minor Road Approaches

II~

Approach Reduced to Single Carriageway Approach Incorporating V-turn Facility

Figure 6.18 Minor Road Dual Carriageway Approaches



Carriageway Widths Around CornersWhere carriageways are taken around cornersand short radius curves, added width shall beprovided to cater for the swept path of larger"goods vehicles and the "cut in" of traiier units.Table 6.5 shows the recommended minimumwidths for various nearside curve radii based onthe Class 12 design vehicle. For radii above100m, the standards set out in Table 3.5 shallbe used.

SECTION 6

On single lane sections greater than 50m inlength, the allowance given in Table 6.5 shall bemade for broken down vehicles. However, theengineer must be careful not to use thisadditional width in iocations that may encourage2 lane flow to develop, ego at intersection rightturn lanes.

•

Inside Single Lane Width Single Lane Width with Two Lane Width for One Way or Two Way TrafficComer/Curve (Excluding Edgestrip Space to Pass Stationary (Excluding Edgestrip Provision)

Radius Provision) Vehicles (Including (m)(m) (m) Edgeslrip Provision)

Inside Lane Outside Lane Tolal(m)

10 8.4 10.9 8.4 6.5 14.9

15 7.1 9.6 7.1 6.0 13.1

20 6.2 8.7 6.2 5.6 11.8

25 5.7 8.2 5.7 5.2 10.9

30 5.3 7.8 5.3 5.0 10.3

40 4.7 7.2 4.7 4.6 9.3

50 4.4 6.9 4.4 4.3 8.7

75 4.0 6.5 4.0 4.0 8.0

100 3.8 6.3 3.8 3.8 7.6

Tabie 6.5 Minimum Corner and Curve Radii and Carriageway Widths

" a lb

- c - ~~__=~ ~=~ L3S~

c-- - -.,... - -7;===========-

~ f J Va. Turning Length (+Queuing Length

if required, see clause 6.7.8)

b. Deceleration Length (6.7.10)

Figure 6.19 Major/Minor Junction with a Ghost Island

January 1997

c. Through Lane Width (6.7.5)

d. Turning Lane Width (6.7.6)

e. Direct Taper Length (6.7.9)

Page 6/19


6.7.6 Central Islands • Major Road

Ghost IslandsFor new junctions, the desirabie width of a ghostisiand turning lane shail be 4.0m, but arelaxation to 3.0m is permissible. At urban andsuburban junctions, it can sometimes beadvantageous to use a greater width notexceeding 5.0m to ailow a degree of shelter inthe centre of the road for large goods vehiclesturning left from the minor road to execute theturn in two separate manoeuvres.

For improvements to existing junctions, wherespace is very limited, a reduced width may beunavoidable. The width of ghost islands shallnot bEl less than 205m.

At righVleft staggered junctions, the decelerationlengths would overlap but the width of the ghostisland shall not be increased to make them lieside by side. The starting points of the leftturning section shall be joined by a straight line,which will mean at higher design speeds, the fullwidth of the turning lane will not be developeduntil the end of the diverging section (as shownin Figure 6.10). The width of the turning laneshail be the full width of the ghost island.

Physical IslandsAt single lane duailing and dual carriagewayjunctions, the width of the central island at thecrossing point shall be 10.0m, including medianhardstrips. This width will shelter most largegoods vehicles turning left from the minor road,except for very long vehicles. In exceptionalcircumstances where use by very long vehiclesis expected and a roundabout is not feasible, awidth of 14.0m including hardstrips wiil beneeded to shelter the largest articulatedvehicles (1605m) and a width of 16.5m includinghardstrips will be required to shelter drawbartrailer combinations (20.0m). The minimumwidth of a physical island, usually located at theend of the direct taper shall be 3.5m.

Crossing left turn movements within the centralisland can usefuily be separated by physical orpainted guide islands set out with road markingsso that the number of traffic conflicts at anypoint is reduced. Painted guide islands can beenhanced by the use of coloured surfacing ortextures within them, block paving, roadmarking or traffic studs. However, designswhich have numerous small traffic islandsshould be avoided as they are confusing andtend to be ignored.

Preventing or minimising conflicts by separationmeans that drivers are only faced with simpledecisions on their choices of movement at any

January 1997

SECTION 6

one time. This can lead to greater safety. Forthe separation to be effective, the junction mustbe large enough for drivers to identify inadequate time those vehicles which wiil conflictwith their intended path and those that wiil not.If this is not so, gaps in the flow cannot be usedeffectively by traffic entering the junction.

6.7.7 Central Island Tapers

Central isiands, whether for ghost isiands(Figure 6.20) or single lane dualling (Figure6.21) should normally be developedsymmetrically about the centreline of the majorroad to their maximum width at the tapersshown in Table 6.6. The maximum island widthshould continue through the junction to thetangent point of the minor road radius and theedge of the major road carriageway.

Design Speed Taper for Ghost Taper for(kph) Island and Single Dual

Lane Quailing Carriageways

50 1:20 1:4060 1:20 1:4070 1:20 1:4080 1:25 1:45100 1:30 1:50120 _. 1:55140 -- 1:60

Table 6.6 Tapers for Central Islands (1 :T)

T R--__~""1~---.J.1-<>-=~~~'S.>:..'-S=~---

9 t a

R

T.Ghost Island Taper (1:T)

R. Rounding (50mR Typical)

Figure 6.20 Ghost Island Development

For single lane dualling, the central islandshould be introduced by means of hatchedmarkings until there is sufficient width toaccommodate the appropriate sign on the noseof the physical island with the required runningclearances to it.

Page 6/20

•

•

..


T E

=====-==~'==::d:l~

'\ . ! ~"- 'Road Sign

T. PhysIcal Island Taper (1 :T)

Figure 6.21 Physical Island Deveiopment

6.7.8 Turning Length in Median (a)

The turning length is provided to allow longvehicles to position themselves correctly for theleft turn. The turning length should be aminimum of 10m long irrespective of the type ofjunction, design speed or gradient, measuredfrom the centreline of the minor road. It isshown on Figure 6.19.

Where capacity calculations indicate that forsignificant periods of time there will be vehiclesqueuing to turn left from the major road, theturning length shall be increased to allow for areservoir queuing length to accommodate suchvehicles. For simplified calculation of storagelength refer to Section 5.10.

Where reservoir provision appears desirable ata junction with ghost islands, consideration shallbe given to providing physical islands instead toafford greater protection to turning traffic.Where site conditions prevent this, the reservoi'rspace may still be provided.

6.7.9 Direct Taper Length (e)

The direct taper length is the length over whichthe width of a left turning lane is developed. Forghost islands and physical islands in single lanedualling and dual carriageway junctions, leftturning lanes shall be introduced by means of adirect taper whose length is part of thedeceleration length and depends on the designspeed. This taper iength is given in Table 6.7and illustrated in Figure 6.19.

Design Speed Direct Taper(kph) Length· e (m)

50 560 570 1580 15100 25120 30140 35

Tabie 6.7 Direct Taper Length - e

January 1997

SECTION 6

6.7.10 Left Turning Lanes

Left turning tapers and lanes in the centre ofghost islands, and single lane dualling areespecially useful as they provide a convenientspace for vehicles to slow down and wait beforeturning off the major road. These junctionlayouts can also assist the left turn out of theminor road.

The overall length of a left turning lane providedat ghost island, single lane dualling and dualcarriageway junctions will depend on the majorroad design speed and the gradient.

It consists of a turning length, as described inClause 6.7.8, and a deceleration length. Thiscomponent shall be provided in accordancewith Tables 6.8 and 6.9, in which the gradient isthe average for the 500m length before theminor road.

Design Up Gradient Down GradientSpeed(kph) 0-4% Above O~4% Above

4% 4%

50 25 25 25 2560 25 25 25 2570 40 25 40 4080 55 40 55 55100 80 55 80 80120 110 80 110 110

Table 6.8 Deceleration Length - b (m) forGhost Island and Single LaneDualling

Design Up Gradient Down GradientSpeed(kph) 0-4% Above 0-4% Above

4% 4%

50 25 25 25 2560 25 25 25 4070 40 25 40 5580 55 40 55 80

100 80 55 80 110120 110 80 110 150140 150 110 150 200

Table 6.9 Deceleration Length - b (m) forDual Carriageways

The deceleration length can be seen on Figure6.19. The deceleration length is based on theassumption that vehicles will slow by onedesign speed step on the trunk road beforeentering the length. The deceleration rate onthe level is assumed to be 0.375g. There is noreaction time as this is a planned manoeuvre.

Page 6/21


6.7.11 Median Openings

The opening in the median for single lanedualling at the crossing point shall be 15.0mwide.

Problems have been experienced with driverconfusion over priority within the median,particularly where the width of the physicalIsland has been increased to cater for largegoods vehicles.

Measures to regularise the priority arrangementwithin the median opening include channelizingthe central area.

illustrated in Figure 6.29. Opposite the refugeopenings, dropped kerbs shall be installed toaid pedestrians.

6.7.13 Nearside Diverging Tapers andAuxiliary Lahes

Nearside Diverging TaperMajor road traffic, when slowing down on theapproach to a junction in order to turn into aminor road, may impede following vehicles thatare not turning. It is helpful, therefore, to permitthe divergence of the two streams at a smallangle by the provision of a nearside divergingtaper.

Consideration may also be given in thesecircumstances to introducing differentialcoloured sUrfacing or studs to enhance the roadmarkings or indicate the area of allowableoverrun for large goods vehicles. However,such coloured surfacing should also be visibleat night and in poor weather conditions.

Nearside diverging tapers are of iess benefit interms of operation and safety than left turninglanes because the right turn from the majorroad does not cross an opposing traffic streamand is rarely impeded. However, nearsidediverging tapers should always be consideredfor higher speed roads or on gradients. •

6.7.12 Traffic Islands

Traffic islands can be ghosted or kerbed(physical) and should be provided in the mouthof the minor road at major/minor junctions(except at simple junctions) to:

Where a traffic island serves as a refuge forpedestrians, it shall be at least 1.5m wide andhave openings in the centre at carriageway levelto make the crossing easier for pedestrians (seeClause 5.12). The recommended layout anddetails of the design of channelizing islands are

Physical traffic islands shouid be positioned inurban situations only, shall have an area of atleast 4.5 square metres, and shall be treated tobe conspicuous in poor lighting conditions.Smaller areas should be defined by roadmarkings. The risk of overriding the islands canbe reduced by offsetting the approach nosefrom the edge of the vehicle paths.

•Where the percentage of large goodsvehicles is greater than 20%, and thevolume of right turning traffic is greaterthan 450 vehicles AADT (one-way).

Where the junction is on an up or downgradient of greater than 4% at any designspeed and the volume of right turningtraffic is greater than 450 vehicles AADT(one-way).

Where the volume of right turning trafficis greater than 600 vehicles AADT (oneway).

•

•

•

Nearside diverging tapers shall not be providedat simple junctions (Clause 6.6.1). They shallbe provided at junctions between major andminor roads where the design speed for themajor road is 80 kph or above. They shall beprovided at other junctions in the followingcircumstances for traffic in the design year:

Where the major road traffic flow is greater than7000-8000 AADT (one-way), then the figuresgiven above for turning traffic should be halved.

Nearside diverging tapers shall not be providedwhen the minor road is on the Inside of a curvewhere traffic in the diverging lane couldadversely affect visibility for drivers emergingfrom the minor road. They shall generally notbe provided where the design speed for themajor road Is less than 80 kph nor where thecost of provision is excessive. In this case,adequate warning of the junction ahead mustbe provided.

Channeiize intersecting or merging trafficstreams

Give guidance to long vehicles carryingout turning movements

Assist pedestrians.

Provide shelter for vehicles waiting tocarry out manoeuvres, such as waiting toturn left

Warn drivers on the minor road that ajunction is ahead

•

•

•

•

•



Nearside diverging tapers shall be formed by adirect increase to a width of 4.0m contiguous tothe corner into the minor road. A radius of atleast 20m should be used where the main roaddesign speed is 80kph and at least 40rn abovethis speed. The width around this corner willdepend on the radius selected. The length ofthis lane is defined as being from the beginningof the taper up to the start of the radius, asshown in Figure 6.22.

The desirable length of a nearside divergingtaper shall be that of the relevant decelerationlength given in Tables 6.8 and 6.9.

Auxiliary LaneAt major road flows of over 7000-8000 AADT(one-way), vehicles decelerating on the maincarriageway and moving into the diverging taperto a point where there is a full lane widthavailable in the diverging taper may have asignificant effect on the capacity of the throughcarriageway by impeding following drivers.

SECTION 6

In this instance, consideration shouid be givento the provision of a nearside auxiliary laneinstead of a taper for diverging traffic. Theprovision of an auxiliary lane, as shown inFigure 6.23, would allow turning traffic to moveoff the mainline prior to any deceleration.

The auxiliary lane should be of sufficient lengthto allow for the speed change from the majorroad to the turn into the minor road and wouldnot normally be less than 80m. Its length mayalso depend on any need for reservoir space forturning traffic. The auxiliary lane shouldcommence with a direct taper (Figure 6.23), thelength of which shall be determined from Table6.7. The taper should be that used for a leftturning lane for a single lane dualling or dualcarriageway junction, with the relevantdeceleration length given in Tables 6.8 and 6.9.

E

~~=~~~~~~~t _1-.. --_--'aL-..-- .~

a. Deceleration Length

Figure 6.22 Major/Minor Junction with Nearside Diverging Taper

E

============~~

b I,a

a. Deceleration Lengthb. Direct Taper Length

Figure 6.23 Major/Minor Junction with Nearside Auxiliary Lane



6.7.14 Merging Tapers

Merging tapers permit minor road traffic toaccelerate fully before joining the faster trafficstreams on the mainline where the joining trafficmay otherwise impede flow or be a hazard(Figure 6.24).

Merging tapers shall oniy be used at dualcarriageway junctions. They shall be providedgenerally where the major road design speed is80 kph or above, or when and the volume ofright turning traffic in the design year exceeds600 vehicles AADT (one-way).

However, where the merging taper is for anupgradient of greater than 4% or where thepercentage of large goods vehicles exceeds20%, the threshold value may be reduced to450 vehicles AADT (one-way).

Merging tapers shall never be used at singlelane dualling junctions.

At some junctions on dual carrlageways, theremay be safety benefits in providing mergingtapers at lower flows.

a

SECTION 6

A separate turning lane, with a radius of at least25m where the main road design speed is 80kph, and at least 30m above this speed, shallbe used to introduce the merging taper from theminor road. The initial width of the lane, whichwill depend on the radius of the turning lane(determined from Table 6.5), should bedecreased at a constant taper depending on thedesign speed.

The lengths of the tapers to be used are givenin Table 6.10. The minimum initial width of amerging taper shall be 4.0m.

On dual carriageways, with a design speed of120 kph or greater, the merging taper may bepreceded by a short nose of 40m length formedbetween it and the end of the 30m approachcurve. The back of the nose should have aminimum width of 2m (Figure 6.25).

Design MergingSpeed Length ~ a(kph) (m)

80 90100 110120 130140 150

Table 6.10 Merging Length - a

-----------------~----

E"!...

a. Merging Length

Figure 6.24 Major/Minor Junction with Nearside Merging Taper



a b

SECTION 6

Nose 2m minimum --...........1'-2------------~~~-~

o....

•

a. Merging Lengthb. Nose Taper

~#o

Nose~N#

_ .= = Z::Z>Z2>55...Q _Shoulder

Figure 6.25 Major/Minor Junction with Nearside Merging Taper (Allernative for Dual Carriageway witha Design Speed of 120 kph)

6.7.15 Stagger Distances

The stagger distance of a junction is thedistance aiong the major road between thecentrelines of the two minor roads.

Left/Right StaggerFor simple major/minor junctions with a lefVrightstagger, the minimum stagger distance shali be40m.

For a ghost island junction the stagger distanceshali be 50m and for a junction with single lanedualiing it shali be 40m. These are based onthe distance required for manoeuvring the20.0m drawbar trailer combination designvehicle between the two minor roads, and shallbe provided on all new staggered junctions,including the upgrading of rural crossroads,where large vehicles are expected.

Right/Left StaggerThe minimum values for staggered right/leftmajor/minor junction are given in Table 6.11.For higher design speeds, the distance is basedon the sum of the two deceleration lengths lyingside by side plus the turning lengths (andqueuing lengths, if appropriate) at each end, asindicated in the table. Otherwise it is based onthe manoeuvring requiremenls of the designvehicle.

January 1997

Design Stagger DistanceSpeed (kph) (m)

Ghost Island Single LaneDualling

50 50 (Manoeuvring) ..

60 50 (Manoeuvring) ..

70 60(10+40+10) ..

80 75{10+55+10) 75(10+55+10)

100 100 (10 + 80 + 10) 100 (10 + 80 + 10)

Table 6.11 Minimum Stagger Distance forRight/Left Staggered Junction

6.7.16 Skew Junctions

The design parameters where the minor roadapproaches at an angle other than 90', for bothleft hand and right hand skew junctions, areshown in Figure 6.26. The geometricparameters are set out in Clauses 6.7.5 to6.7.12.

Page 6/25

•SECTION 6

- -~~ _-::::--_

~==~~===~~~~~I. b .~

A------.,---.=..-::_=-=-=-=-:-:;- = = =


/:/

/

f;H

A e k;\--------r-=--==---=-=-=-::-:-=--,= = = = - -~- - -~-

~= - ~:=== - ~~~,............... _ C _

---------------

I, b .1.a.1

•

a. Turning Length (+ Queuing Lengthif required, see ciause 6.7.8)

b. Deceleration Length (6.7.10)

c. Through Lane Width (6.7.5)

d. Turning Lane Width (6.7.6)

e. Minor Road Entry Width (6.7.5)

Figure 6.26 Major/Minor Junction with Skew Minor Road


•


6.7.17 T-Junction with CarriagewaySeparation

On dual carriageways, left turn crossingmanoeuvres at the junction are prevented andfacilities shall be provided nearby for turningtraffic, as highlighted in Clause 6.6.5. Onemethod of achieving this is to provide aninterchange, the principle of which is shown inSection 7. The design of such crossings isoutlined in the following paragraphs and therlght-in/right-out connections to the mainline areillustrated in Figures 6.27 and 6.28.

Preventing left turns removes the need tosignalize the carriageways on the major road tocater for these movements. The major roadcarriageway can pass through the junction at aconstant width. Two right-in/right-outconnections are used with an overbridge orunderpass. These junctions should bedesigned in composite form, as described inthis section, catering for the right turnmovement only.

For the right turn merge to the main road, theminor road channelizing Island shown inFigures 6.27 and 6.28 shall be designed so asto provide a constant width of turn into themajor road. The width shall be determined fromTable 6.5. The detail of the island asapproached aiong the minor road is as set outin Ciause 6.7.18. If there is a merging taper asshown in Figure 6.28, the widths and tapersshall be as set out in Clause 6.7.14. Thehatched markings shall be extended from theminor road centreline to link with those for themerge taper, the channelizing island beingprovided within them, as in Figures 6.27 and6.28. .

For the right turn diverge from the major road,the channelizing island described in Clause6.7.12 and shown in Figures 6.27 and 6.28 shallbe designed so as to provide a constant widtharound the turn to the minor road. The widthshall be determined from Table 6.5. Where anearside diverging taper or nearside auxiliarylane is present (see Figures 6.22 and 6.23), thehatched markings should be extended alongtheir current path until the intersection with thecentreline of the minor road, and thechannelizing island shall be provided withinthem. This is shown in Figures 6.27 an 6.28.

The right-in/right-out connections can also beused with the compact interchange detailed inSection 7. It offers a cheaper but morerestricted form of grade separation where theeconomic case for a full interchange cannot befully justified. The connector roads between the

January 1997

SECTION 6

right-in/right-out connections shall be designedin accordance with Section 7.

Traffic shall be introduced to the right turn laneby a nearside diverge or auxiliary iane inaccordance with Clause 6.7.13.

Traffic leaving the right turn lane should "GiveWay" or merge with the major road traffic inaccordance with Clause 6.7.14, or join anadded lane, depending on the major roaddesign speed, traffic flows and layout.

Page 6/27


Figure 6.27 T·Junction with Carriageway Separation

SECTION 6

Channellslng Island flared togive constant carriagewaywidth around the turn

•

•

c

a. Diverge Taper

b. Nose Taper

ba

~------------------

c. Merge Taper

d. Curve Widened Lane

•

Figure 6.28 T·Junction (Alternative for Dual Carriageway with a design speed of 120kph).



6.7.18 Channelizing Islands b)• T-JunctionThe recommended channelizing island iayoutfor T-Junctions or staggered junctions, wherethe minor road centreline is inclined to the majorroad at an angle of between 70' or 110', isshown in Figure 6.29: This shouid be read inconjunction with Tables 6.12 and 6.13. c)

The following points shouid also be noted:d)

a) "Edge of major road carriageway" meansedge of major road travelled way.

b) The circular arc R, is tangential to theoffset, d, from the minor road centrelineand the offside edge of the through trafficlane on the major road into which left e)turning traffic from the minor road willturn.

c) By striking a circular arc of radius (R, + 2)metres from the same centre point as arcR, to intersect the edge of the major roadcarriageway, point A is established wherea straight line drawn from the centre pointof arc R, to this intersection crosses R,.

d) The circular arc R2 is tangential to theoffside edge of the major road offsidediverging lane and also passes throughpoint A.

e) Radius R2 is normally the same value asR, but should be designed to ensure thatthe island nose is positioned between 2 -4 metres from the edge of the maincarriageway and that the width of theisland lies between 2- 5 metres.

f) The design ensures that left turning trafficfrom the major road will not clash withtraffic waiting to turn left from the minorroad.

Skew JunctionsThe design of a channelizing island for skewjunctions is similar to that outlined above, butthe following points should be noted:

a) The centreline of the minor road is turnedwith a radius of at least 50 metres to meetthe edge of the major road at right angles.

January 1997

SECTION 6

For right hand skew junctions, the islandshould be about 15 metres long. The lefthand side of its tail (viewed from theminor road approach) should touch thecurved minor road centreline and berounded off at a radius of 0.75m to1.00m.

The offset, d, for right hand skewjunctions is 4.5 metres.

For left hand skew junctions, the circulararc R, touches the curved minor roadcentreline and is tangential to the offsetedge of the through traffic lane on themajor road into which left turning trafficfrom the minor road will turn.

The island should be about 15 metreslong. The tail is offset about 1m to the leftof the curved minor road centreline(Viewed from the minor road approach)and rounded off with a radius of O.75m to1.00m.

Page 6/29


Centreline of __-Iminor road

SECTION 6

•

o..,.

0.75mR(min)

0.75-1.0mR2.5

d

Edge ofmajor road

carriagewa"y'-+3-_-"'-L---'<,.---¥ifrr_---,;L- -'---,_

Figure 6.29 Design of Channelizing Isiand

Minor Road Offset - dInclination - 8" (m)

70 1.5$0 2.090 2.5

100 2.0110 1.5

Table 6.12 Channelizing Island Offset

Width of Major Road Radius - R,Carriageway at (m)

Junction - w(m)

7.3 12

11.3 (Ghost Island) 14

17.3 (Single Lane Dualling) 22

Table 6.13 Design of Radius R,



6.7.19 Splitter/Right Turn Islands

Splitter/right turn islands may be used tochanelize traffic flows and separate conflictpoints within a junction.

They have additional benefits of reservingspace for signing and aiding pedestrianmovement by proViding a refuge at bUSyjunctions. Refer to Figure 6.30.

Corner radii and carriageway widths given inTable 6.5 shall be used to construct the rightturn lane. The raised island shall beconstructed to give shy distances to travelledways as illustrated in Figure 6.30.

Splitter islands are particularly useful atsignalized junctions where minor road right turntraffic can be controlled by "Give Way" signsand markings rather than signals.

Traffic shall be introduced to the right turn laneby a nearside diverge or auxiliary lane inaccordance with Clause 6.7.13.

SECTION 6

Traffic leaving the right turn lane should "GiveWay" or merge with the major road traffic inaccordance with Clauses 6.7.4 or 6.7.14, or joinan added lane, depending on the major roaddesign speed, traffic flows and layout.

6.7.20 Drainage and Crossfall

From considerations of surface water drainageand driver comfort, the road camber on themajor road shall be retained through the junctionand the minor road graded into the channel lineof the major road. Checks shall be made for flatareas at all changes of gradient. superelevationof crossfall. Refer to Section 8.

Edge ofTravelled

A = Inside Corner Radius

RW = Outside Corner Radius

W = Lane Width

r = O.5m Aadius

"i<r1 Hatched Marking

Figure 6.30 Typical Layout of Splitter Island



6.7.21 Traffic Signs and Road Markings

The need for, and layout of, traffic signs androad markings is an integral part of the designprocess and no junction design is completewithout these features having been inciuded.Advance direction and warning signs shall beprovided, and care must be taken with thepositioning and size of signs at the junctionitself so that they do not interfere with drivers'visibility requirements. These matters need tobe considered from the earliest stage as theycan fundamentally affect layout and hence iandacquisition requirements. Advance signing onminor roads may need particularly carefulconsideration. Refer to the Qatar TrafficManual for details of signing and marking.

6.7.22 Road Lighting

Road lighting is normally provided atmajor/minor junctions in rural areas only whenan intersecting road has lighting. When anexisting junction is being modified, the lightingprovision should be checked for suitability withthe new arrangement. Any alteration should becarried out prior to, or at the same time as theroadworks. Refer to Section 10.

January 1997

SECTION 6

Page 6/32

•

•

.'13,

..QATAR HIGHWAY DESIGN MANUAL

6.8 ROUNDABOUTS - GENERAL

This section defines the main types ofroundabouts that can be used for an at-gradejunction of any class of road.

The requirements are defined in relation to the.size of roundabouts, effect of approach speed,visibility, entry width, entry deflection and thecirculatory carriageway.

The recommendations for siting of roundaboutsare given in Clause 6.1 .4.

6.8.1 General Principles

The principal objective of roundabout design isto secure the safe interaction of traffic betweencrossing traffic streams with minimum delay.This is achieved by a combination of geometriclayout features that, ideally, are matched to thevolumes of traffic in the traffic streams, theirspeed, and to any locational constraints thatapply.

There are two broad regimes of roundaboutoperation. The first occurs in urban areas withhigh peak flows, often with marked tidalvariations and physical restrictions on the spaceavailable. The second regime occurs in ruralareas and is characterised by high approachspeeds, low tidal variation and few physicalconstraints.

Entry width is an important feature thatdetermines entry capacity and often needs to belarger in urban situations than in rural cases.On the other hand, the most importantdeterminant of safety is vehicle deflectionimposed at entry because this governs thespeed of vehicles through the junction. It isparticularly important whenever approachspeeds are high. Entry deflection is related tothe entry path curvature and limiting this radiusof curvature in the vicinity of the entry to 100mmaximum ensures that sufficient deflection willbe undergone by entering vehicles to limitthrough speeds.

The characteristics of roundabout accidents andtheir frequencies in relation to geometric layoutdesign and traffic flows have been studied inthe UK by Transportation Research Laboratory(TRL). The relationships derived from thesestudies have provided insights into how variousaspects of design interact to influence the typesand frequencies of accidents at roundabouts.These relationships therefore, constitute thefundamentals of design for safety. Asrelationships between aspects of design are notalways mutually compatible, minimising thelikely incidence of a particular type of accident

January 1997

SECTION 6

may increase the potential for another. Design,therefore is a trade-off between operationalefficiency, minimising delays at the junction, andvarious safety aspects within whichever locationconstraints apply. The latter are often thedominating factor when designingimprovements to an existing junction,particularly in urban areas.

Consideration of the need for, and layout oftraffic signs and road markings should be anintegral part of the design process. Referenceshould be made to the Qatar Traffic Manual.

The provision of road lighting at roundaboutsshould normally be regarded as an essentialsafety requirement. Sometimes lightingrequirements may conflict with environmentalconsiderations. However, it should berecognised that roundabouts are generally saferthan other forms of at-grade junctions and thedecision to use a roundabout should not beabandoned solely because of lighting problems.In sensitive locations it may be possible to adoptalternative lighting methods and other measuresto make the roundabout more visible. When anexisting roundabout junction is being modified,the lighting layout should be checked forsuitability with the new road arrangement andany alteration carried out prior to, or at the sametime as the roadworks. It is important thatapproaching drivers see and perceive that theyare approaching a roundabout and are notmisled by the projection of the lighting layout,particularly at times of poor visibility.

6.8.2 Types of Roundabout

Defin itionsThe preferred main type of roundabout to beused in Qatar is the Normal Roundabout. Thereare other forms such as Mini and DoubleRoundabouts, and other variants of these basictypes, ie. Ring Junctions, InterchangeRoundabouts and Signalized Roundabouts.

Normal RoundaboutA roundabout having a one-way circulatorycarriageway around a kerbed central island 4mor more in diameter and usually with flaredapproaches to allow multiple vehicle entry.(Figure 6.31).

The number of entries recommended is either 3or 4. Roundabouts per10rm particularly well with3 arms, being more efficient than signals,provided the traffic demand is well balancedbetween the arms.

Page 6/33


a Traffic deflectionIsland

Figure 6.31 Normal Roundabout

If the number of entries is above 4, drivercomprehension is affected and the roundaboutbecomes larger with the probability that highercirculatory speeds wiil be generated.

Interchange RoundaboutsThe foilowing examples of interchanges arediscussed in Section 7 Interchanges.

• Two bridge roundabout

• One bridge and two roundabouts(dumbbell)

• Ring junction interchange.

Signalized RoundaboutAs with Major/Minor Junctions, traffic signalscan be installed at roundabouts to improvesafety or traffic capacity. Traffic signals can beused at one or more of the approach arms oreven on the circulatory carriageway on somelarge roundabouts.

January 1997

SECTION 6

Page 6/34

•


6.9 SAFETY AT ROUNDABOUTS

6.9.1 General

•SECTION 6

Design to encourage slow entry to thejunction and quick exit to leave thejunction clear for the next users.

It is generaliy known from studies that feweraccidents occur at roundabouts than atsignalized junctions of similar traffic flows. Theseverity of accidents is also much iess than atother junctions.

Measures to reduce accidents at existingroundabouts with poor safety records include:

• Repositioning or reinforcement of warningsigns

Additional safety aspects to be considered indesigning a layout include:

Care must be taken in layout design to securethe essential safety aspects. The mostcommon problem affecting safety is excessivespeed, both at entry or within the roundabout.The most significant factors contributing to highentry and circulating speeds are:

• Angle between arms: The accidentpotential of an entry depends on both theangle (anticlockwise) between itsapproach arm and the previous approacharm, and the traffic flows. A high flowentry should have a large angle to thenext entry, and a low flow entry a smalierangle in order to minimise accidents

•••

••

•

•

•

•

•

Inadequate entry deflection

A very acute entry angle whichencourages fast merging manoeuvreswith circulating traffic

Poor visibility to the "Give Way" line

Poorly designed or positioned warningand advance direction signing

"Reduce Speed Now" signs, whereprovided, being incorrectly sited

More than four entries leading to a largeconfiguration.

Gradient: Whilst it is normal to flattenapproach gradients to about 2% or lessat entry, research at a limited number ofsites has shown that this has only a smalibeneficial effect on accident potential

Visibility to the left at entry: This hascomparatively little influence uponaccident risk. There is nothing to begained by increasing visibility above therecommended level

Crest Curves: Junctions should not besited on crest curves where the approachsight to the roundabout is impaired

•

•

•

•

•

•

•

Provision of map type advance directionsigns

Making the "Give Way" line moreconspicuous.

Moving the central island chevron signfurther to the right to emphasise the angleof turn, placing another chevron signabove the normal position, and placingchevron signs in the median in line withthe offside lane approach on dualcarriageways. Chevron boards canimpinge on circulatory visibility but theeffects can be minimised by positioningthe boards (and associated turn rightsign) 2m back from the central islandkerbline

When approach speeds are low (usualiyin urban areas), a ring of contrastingpaving can be laid in a chevron patterninside the central island perimeter at agentle slope, refer to Clause 5.19.

In rural areas it is not recommended toinstali raised kerbed. chevrons onroundabouts. Experience has shown thatphysical obstructions such as chevronkerbing wili be hit inadvertently at nighttime by vehicles whose drivers are notaware of the junction ahead. Chevronsigns should be placed in these locationsonly

Landscaping where approach speeds arehigh in urban areas can provide a usefulsupplement

Provision of "Yeliow Bar Markings" on fastdual carriageway approaches has shownthat a 57% reduction in accidents can beachieved. This is from studies carriedout in the UK by the TRL

Provision of appropriate levels of skiddingresistance on the approaches toroundabouts and on the circulatorycarriageways



It should be noted that at the speed oftraffic on a circulatory carriageway,skidding resistance is derived from thesurface texture of the aggregates whichform the surface of the road (the microtexture). Particular consideration shouldbe given to ensure that the aggregatesused have skid resisting propertiesappropriate to the circumstances

•

•

•

The deep surface texture (the macrotexture) necessary for good skidresistance on high speed routes is notrequired for circulatory carriageways.Deep surface texture is requiredhowever, on the approaches toroundabouts if the design speed of trafficis greater than 120 kph

Avoidance of abrupt and excessivesuperelevation in the entry region

Reduction of excessive entry width byhatching or physical means

Provision of "Reduce Speed Now" signsand/or "Count-down" markers

If entry problems are caused by poor visibility tothe left, good results can be achieved bymoving the "Give Way" line forward inconjunction with curtailing the adjacentcirculatory carriageway by hatching or extensionof the traffic deflection island.

6.9.2 Two Wheeled Vehicles

Though roundabouts have an impressiveoverall safety record for most vehicle types, thisdoes not apply equally to two wheeled vehicles.Research has shown that at four-armroundabouts in the UK, injury accidentsinvolving two-wheeled vehicles constitute abouthalf of those reported. The proportion ofaccidents involving cyclists is about 15%,although they typically constitute less than 2%of the traffic flow.

The accident involvement rates for two-wheeledvehicles, expressed in terms of accidents perroad user movement, are 10-15 times those ofcars, with pedal cyclists generally having slightlyhigher accident rates than two-wheeled motorvehicles riders.

The study at four-arm roundabouts by the TRLin the UK has shown for example that, in 50 and60 kph posted speed areas, there aredifferences in pedal cycie accident involvementrates for different categories of roundabouts.Engineers should be aware of the following:

• Normal roundabouts with small centralislands and flared entries have accident

- rates which are about twice those ofnormal roundabouts with large centraiislands and unflared entries. Thisrelationship appears to apply consistentlyfor all types of vehicular road users. Aspreviously stated, analysis of accidentdata suggests that when all types ofaccident are considered, entry deflectionis the most important factor

• Reduction of the circular width byinsertion of a central island collar.

Care should be taken with the choice of kerbtype for roundabout design. A safety probiemcan arise where certain specialist, high profilekerbs are used around a central island as theycan be a danger to vehicles over-running theentry. Observations have shown that thesekerbs can result in loss of control or overturningof vehicles unless the approach angle is smalland actual vehicle speeds are low. Wherehigh profile kerbs are to be used onapproaches, the kerbs can be hazardous forvehicles and pedestrians, and considerationshould be given to the provision of pedestrianguardrails. Care shouid be taken to ensure thatvisibility sightlines are maintained.

High circulatory speeds cause associated entryproblems and normally occur at largeroundabouts with excessively long and/or widecirculatory carriageways. Excessive circulatoryspeeds can also be caused at smallerroundabouts by inadequate deflection atprevious entries. The soiution to highcirculatory speeds usually has to be fairlydrastic, involving the signalization of problementry arms at peak hours. In extreme casesthe roundabout may have to be converted to aring junction in which the circulatorycarriageway is made 2-way and theentries/exits are controlled by Individual normalroundabouts or traffic signals.

January 1997

•

•

70% of pedal cycle accidents at smallernormal roundabouts are of the'entry/circulating' type, for example, motorvehicle entering roundabout collides withpedal cycle crossing entry

At dual carriageway roundabouts, theaccident involvement rate for cyclists isabout two to three times greater than thatat dual carriageway traffic signals, but forcars, the opposite is true.

Page 6/36


6.9.3 Large Goods Vehicles

The problem of large goods vehiclesoverturning or shedding their loads atroundabouts has an obvious solution in relationto layout geometry. Whilst in the UK there areonly about 60 personal injury accidents a yearin this category, there are considerably moredamage-only accidents. Load shedding ofteninvolves great congestion and delay, and isexpensive to clear, especially if occurring atmajor junctions. Experience suggests thatroundabouts where these problems persistusually exhibit one or more of the followingfeatures:

SECTION 6

• Inadequate entry deflection leading tohigh entry speeds

•• Long straight sections of circulatory

carriageway leading into deceptively tightbends

• Sharp turns into exits

• Excessive crossfall changes on thecirculatory carriageway

• Excessive adversenearside lane ofcarriageway.

crossfall on athe circulatory

An incipient problem for some vehicles may bepresent even if high speeds are not occurring.Research has shown that an articulated, largegoods vehicle with a gravity height of 2.5mabove the ground can overturn on a 20m radiusbend at speeds as low as 24 kph. Particularattention should be paid to ensure thatpavement surface tolerances are complied withand that abrupt changes in crossfall areavoided. It is good practice to make the exitradii greater than the entry radii.



6.10.1 Definitions •

•The Entry Angle: <p, serves as a geometricproxy for the confiict angle between enteringand circulating streams. For roundaboutshaving a curved circulatory carriageway,

I' Average Effective Flare Length

SECTION 6

Inscribed Circle Diameter: D, is the diameterof the largest circle that can be inscribed withinthe junction outline, see Figure 6.32. In caseswhere the outline is asymmetric, the local valuein the region of the entry is taken.

Figure 6.33 Average Effective Flare Length

v. Approach HalfWidth

r. Entry RadiusD. Inscribed

Circle Diameter

A.Point of Maximum EntryDeflection at LeftHand End of Give WayLine

D. Entry Width

Figure 6.32 Geometric Design Features

Entry Width: e, is measured from the point Aalong the normal to the nearside kerb, seeFigure 6.32.

6.10 ROUNDABOUT ELEMENTS

Approach to Half Width: v, is measured at apoint in the approach upstream from any entryflare, from the median iine (or offside edge ofcarriageway on duai carriageways) to thenearside kerb, aiong a normai, see Figure 6.32

Average Effective Flare Length: I', is found asshown in Figure 6.33. The iine GF'D is theprojection of the nearside kerb from theapproach towards the "Give Way" iine, parailelto the median HA and at a distance of v from it.BA is the iine aiong which e is measured (and

is therefore normal to GBJ), and thus D is at adistance of [e-v] from B. The iine CF' is parailelto BG (the nearside kerb) and at a distance of[e-v]/2 from it. Usuaily the line CF' is thereforecurved and its length is measured aiong thecurve to obtain I'.

Sharpness of Flare: S, is defined by therelationship:

S = 1.6[e-v]/1'

and is a measure of the rate at which extrawidth is developed in the entry flare. Largevalues of S correspond to short severe flaresand smail values to long gradual flares.

~ Entry Angle

Figure 6.34 Entry Angle

The line BC is a tangent to the iine EF, which ismidway between the nearside kerbiine and themedian line or the edge of any median islandon the offside, where this line intersects the"Give Way" line. <p is measured as the acuteangle between BC and the tangent to A'D' atthe point of intersection between BC and A'D'shown in Figure 6.34.

For all other roundabouts, the construction isshown in Figure 6.35. The iine BC is the sameas in Figure 6.34. The line GH is the tangent tothe line JK, which is in the foilowing exit,midway between the nearside kerb and the

•



median line or the edge of any median islandon the offside, where this line intersects theouter edge of the circulatory carriageway. BCand GH intersect at L. <IJ is then defined by:

¢ =90-fangle BLG]/2 ie BLH/2

when the right hand side of the equation is. positive.

Entry Anglo ~ Doflnod as (90~-'El/2)

Figure 6.35 Entry Angle

When the right hand side of the equation is zeroor negative, <IJ=O. Angle BLG is measured onthe "outside" of the roundabout, that is, on theside facing away from the central island.

Entry Radius: r is measured as the minimumradius of curvature of the nearside kerbline atentry, see Figure 6.32. For some designs thearc of minimum radius may extend into thefollowing exit, but this is not important providedthat a half or more of the arc length is within theentry region.

Minimum Stopping Sight Distance: asdefined in Section 2.

Entry Path Curvature: This is a measure of theamount of entry deflection to the right imposedon vehicles at the entry to a roundabout, seeClause 6.10.8.

Traffic Deflection Island: a raised area(usually kerbed) on the carriageway, which islocated and shaped so as to direct and alsoseparate traffic movements onto and from aroundabout.

Ghost Islands used for Subsidiary TrafficDeflection: a shaped area, fiush with the roadsurface, delineated by road markings, andwithin the entry width of the approach to aroundabout, so located to deflect and directtraffic movements into the circulatorycarriageway.

January 1997

SECTION 6

6.10.2 Entries

The design of roundabout entries is a complexprocedure, there are several variables whichneed to be addressed to ensure a design whichis safe and has adequate capacity.

The designer has fiexibility in the application ofthe parameters to best meet the partiCUlar siterequirements and constraints. The variablesare:

Entry Width

Flare Length

Entry Angle

Entry Radius

Approach Carriageway Half Width.

6.10.3 Entry Width

It is good practice to add at least one extra lanewidth to the lanes on the entry approach, but asa general rule, not more than two lanes shouldbe added and no entry should be more thanfour lanes wide. The relationship betweenentry width and capacity is quite significant.Entry width is the largest single factor, apartfrom approach carriageway half width, affectingcapacity.

There may be some cases, usually associatedwith low predicted flows, where increased entrywidth is not operationally necessary, but inthese circumstances it is still recommended thattwo entry lanes be provided. This will giveadded fleXibility at abnormal flow periods in thefuture, a passing facility in the event ofbreakdown, and will ease the problem of spaceprovision for long vehicles turning.

Lane widths at the "Give Way" line shall be notless than 3m. Lane widths should be taperedback in the entry fiare to a minimum width of2m. It is generally better to use wide lanewidths because they are more suitable for largegoods vehicles. For example, at a 10m wideentry, 3 x 3.33m lanes are better than 4 x 2.5mlanes.

The development of entry lanes should takeaccount of the anticipated turning proportionsand possible lane bias since drivers often havea tendency to use the nearside lane. The useof lane bifurcation where a lane widens into twoshould maximise use of the entry width. Theuse of short offside lanes is not recommended.

Page 6/39


The alignment of entry lanes is also critical.On rural roundabouts, where design speeds arerelatively high, the kerbline of the deflectionisland (or central reserve in the case of a dualcarriageway) should be on an arc which, whenprojected forward, meets the central Islandtangentially. In urban areas, where designspeeds are lower, this is less important, butnevertheless should be achieved wherepossible. Care should be taken to ensure thatthe resultant entry angle is not too low and thatentry path curvature is not too great.

For capacity assessment, the entry widthshould be taken as the width which drivers arelikely to use. Where the offside kerbline formsa vehicle path which is tangential to the centralislands, the entry width and effective entry widthare the same.

It is usual to consider design flows 15 yearsafter opening for highway schemes. This canresult in roundabout entries with too many lanesfor earlier year flows and lead to operationalproblems. A design year layout will determineoverall geometry and land requirements for theroundabout, but for the early years, it may benecessary for the designer to consider aninterim stage. This approach can result inreduced entry widths and entry lanes.Consideration can also be given to an interimreduction of the circulatory carriageway width,either by an increase in diameter of the centralIsland, or by extending islands forward into thecirculatory carriageway.

6.1'0.4 Flare Design at Entry

SECTION 6

this the design becomes one of link Widening.Where the design speed is high, entry wideningshould be developed gradually, avoiding anysharp angles. In urban areas the use of longflare lengths is often not possible due to landconstraints and capacity may have to beachieved using wider entries and shorter flares.

As a rough guide, the total length of the entryWidening (BG) should be about twice theaverage effective flare length I' (Figure 6.33).

6.10.5 Entry Angle

The effect of entry angle on entry capacity isnegative; as the angle increases capacitydecreases slightiy. However, care shoult;l betaken in the choice of entry angle since highand low angles may result in increased accidentpotential.

The angle should, if possible, lie between 20and 60 degrees. Low entry angles force driversinto merging positions where they must eitherlook over their shoulders to their left or attempta true merge using their mirrors (with theattendant problems of disregarding the "GiveWay" line and generation of high entry speeds).

High entry angles produce excessive entrydeflection and can lead to sharp braking atentries accompanied by "nose to tail" accidents,especially in rural areas. The best entry anglevalue is about 30 degrees. Figures 6.36 and6.37 show two extreme cases.

•

•

Flares on the approach to roundabouts shall besuch that:

a) The maximum entry width shall notexceed 10.5m for single and 15.0m fordual carriageway approach roads

b) The average effective flare length shallnot exceed 100m, but it should be notedthat beyond 30 or 40m any expectedextra capacity is derived fromextrapolation beyond the bounds ofexperimental data and should thereforeby treated with caution.

The capacity of an entry can be improved byincreasing the average effective flare length,though this is of limited effect. A minimumlength of about 5m is desirable in urban areas,whilst a length of 25m is considered adequatein rural areas. Flare lengths greater than 25mmay assist in geometric layout but have littleeffect in increasing capacity. Flare lengthsshould not be areater than 100m. as bevond

January 1997

Entry Angla ill Defined as (90".6/2)

Figure 6.36 Example of Too Low an EntryAngle and also Substandard EntryDeflection

Page 6/40


•

+ Entry angle

Figure 6.37 Example of Too High an EntryAngle and also Excessive EntryDeflection

.' 6.10.6 Entry Radius

For small roundabouts entry capacity increaseswith entry radius up to about 20m, higher radiiresult in very little increase in capacity. Theminimum entry radius should be 6m, a goodpractical design is about 20m. Where aroundabout is designed to cater for large goodsvehicles in particular, the entry radius shouldnot be less than 10m. For large roundabouts(40-60m diameter), large entry radii will almostcertainly result in inadequate entry deflection,for example it will not be possible to achieve thedeflection standard if the entry radius is 100mor more.

6.10.7 Entry Kerbing

As entries are almost always kerbed, hardstripsshould be terminated when entry wideningbegins. The simplest procedure is to place thekerbs at the back of the hardstrip and thenterminate the hardstrip edge line by profiling itback towards the kerbs in a short smooth curveor taper. (See Figures 6.38 and 6.39). This isnot appropriate where there is regular use bycyclists who may wish to continue to the edgeof the circulatory carriageway by using thehardstrip.



a Kerbsb Edge Linesc Edge Line Profiled Back towards the Kerbd Edge of Carriageway

--.... \--.... \

------\'\

\\\\

SECTION 6

•

Figure 6.38 Method of Terminating Edge Strip on Single Carriageway Approach to a Roundabout

1m

1m

...----...... --------------------------

d _--.- -"=~

b

a Kerbsb Edge Linesc Edge Line Profiled Back towards the Kerbd Edge of Carriageway

--------------------_ I----- I

---\-...... \............ \...... \

............ \

'"\\\\

\\\

Figure 6.39 Method of Terminating Edge Strips on Dual Carriageway Approach to a Roundabout



6.10.8 Entry Deflection

Entry Path Curvature is one of the mostimportant determinants of safety atroundabouts. It is a measure of the amount ofentry deflection to the right imposed on vehiclesat entry to the roundabout.

For design purposes oniy, at both new andimproved 'normal' type roundabouts, the vehicieentry path shail be such that when inscribed inaccordance with the foilowing construction, thetightest radius of the entry path curvature shailnot exceed 100 metres.

Construction of the Vehicle PathThe method of construction and measuring theentry path curvature is described beiow, andshown in Figures 6.40 to 6.43. Figure 6.41shows an approach with negative curvature,Figure 6.42 shows an approach with positiveapproach curvature, and Figure 6.43 aroundabout at a "Y" junction.

Assume:

a) The entering vehicle is 2m wide and wiilbe taking the 'straight ahead' movementat a 4 arm roundabout and across thehead of the Tee at a 3 arm roundabout

b) That there is no other traffic on theapproach and on the circuiatorycarriageway

c) That the driver will negotiate the siteconstraints with minimum deflections andthat lane markings by the "Give Way" iinewiil be ignored

d) The initial approach position for entrypath curvature measured from a point notiess than 50m from the "Give Way" iine iswithin the range:

- 1m from the nearside kerb

- 1m from the centreline of a singlecarriageway or 1m from the offsidekerb of a dual carriageway

This will ensure that ail approachalignments are examined and that novehicle path can exceed therecommended maximum radius ofcurvature

January 1997

SECTION 6

e) That the vehicle proceeds towards the"Give Way" line, then:

- It proceeds towards the central islandof the roundabout passing through apoint not less than 1m from thenearside channel or kerb, the positionof which relative to the starting pointdepends on the amount of approachflare to the right (Figure 6.40 and 6.41)

- The vehicle is then assumed tocontinue on a smooth path with itscentreline never passing closer than1m from the central island (it may bemore in some configurations).

Draw, to a scale not less than 1/500 using aflexible curve of equivalent, the centre line ofthe most realistic path that a vehicle would takein its complete passage through the junction ona smooth alignment without sharp transitions.More than one independent assessment of thevehicle paths shail be carried out.

This tightest radius shail be measured bymeans of suitable templates. See "To Measurethe Entry Path Curvature".

The exact path drawn wiil be a matter ofpersonal judgement and the results should beexamined for compliance and consistency withthe appropriate clauses in this section.

One convenient method of construction of thereqUired path is to imagine the advance of ailthe channel or kerb lines and centreline in thecase of single carriageways (together withcentral islands and deflection islands) into thecarriageway by 1m.

The vehicle path wiil be the line of leastresistance, whose centreline will normally, butnot always, be tangential to these constructionlines; in the entry, at the central island and inthe exit. Any reverse of curvature in the vehiclepath around the central island must be drawn sothat there is no sharp deviation between thatcurve and the entry curve. Particular care inchecking entry path curvature is required whenconsidering smail central island designs.

To Measure the Entry Path CurvatureThe entry path curvature is measured on thecurved length of path in the vicinity of the "GiveWay" line (but not more than 50m in advance ofit) between points X and Y (see Figures 6.40 to6.43) about 20m to 25m but not less than 20min length, over which the tightest radius occurs.

Page 6/43


•

Figure 6.40 Determination of Entry Path Curvature

•

•

___ ..L ~~.-J'\\

---- - -- --~~ c ~~~__ ~ ~ ~ Ir

/'" x _----- '..... T1m min./ ----- .....,

/' -\. ...~/ --}<:;--.;\

Figure 6.41 Determination of Entry Path (On a Curved Approach Arm with Negative ApproachCurvature)



\1mmin \,~---

c _L_ Y ~~------~------_,r, .---', 1m mm

----------- X~-- ------·T-----------~-

•a

Figure 6.42 Determination of Entry Path Curvature (On a Curved Approach Arm with Positive ApproachCurvature)

•a. The radius should be measured over a distance of 20-25m;

it Is the minimum which occurs along the approach entrypath in the vicinity of the Give Way line but not morethan SOm in advance of it.

b. Commencement point 1m from the offside kerb for02 or 1m from centre line for S2L, not less than Samfrom the Give Way line.

C. Vehicle entry path curvature.

Figure 6.43 Determination of Entry Path Curvature for a Roundabout at a "Y" Junction



6.10.9 Achieving Entry Deflection

A good method for creating entry deflection onnew schemes where there are no otherconstraints is to stagger the arms, as shown inFigure 6.44. This will help with the overalldesign, reduce the size of roundabouts,minimise land acquisition and assist with theconstruction of "easy" exits.

It is not good practice to generate entrydeflection by sharply deviating the approachroads to the left close to the roundabout andthen to the right at entry. Approach curvesshould be fairly gentle, but there are caseswhen horizontal radii below the minimum for thegeneral design speed of the approach link maybe used, provided always that they areproceeded by the "Roundabout Ahead" warningsign as defined in the Qatar Traffic Manual.However, tight radii will require large amounts ofverge widening to provide adequate forwardvisibility and add to the verge maintenancerequirements.

There is evidence to suggest that a gentle lefthand bend leading to a right hand deflection atentry is more safe than a gentle right handbend.

SECTION 6

In urban areas, the restrictions on spaceavailable coupled with the turning widthrequirements of large goods vehicles maynecessitate small normal roundabouts whichcannot proVide sufficient entry deflection to theright by means of the central island alone. Inthese cases, deflection should be generated bymeans of enlarged traffic islands in the entry,(Figure 6.45).

II. C.ntr.lln. Off..t H:;-20m (Noll 'E••y· Exltl)

Figure 6.44 Entry Deflection by StaggeringApproach Roads

Figure 6.45 Example Showing How Island Design can Increase Entry Deflection at an ExistingRoundabout



6.10.10 Visibility

The forward visibility at the approach to aroundabout shall be as indicated in Section 2 forthe appropriate design speed. This MinimumStopping Sight Distance (SSD) is measured tothe "Give Way" line as shown in Figure 6.46.

The following guidelines represent goodpractice concerning the provision of visibilityand, when subject to relaxation, there is a needfor additional signing to alert drivers of allvehicles to potential hazards.

Eye and Object HeightsVisibilities, with the exception of visibility to theleft at entry and across the central island, shallbe assessed in accordance to Section 2.Visibility to the left and across the central islandshall be obtainable from a driver's eye height of1.05m to an object height of 1.05m, and theenvelope of visibility shall extend to 2.0m abovethe road surface.

Where traffic and direction signs are to beerected on a central reservation, verge, ordeflection island within the envelope of visibility,including to the left, the mounting height shallnot be less than 2.0m above the carriagewaysurface and the envelope checked on sites withchanges of gradient.

Visibility to the LeftDrivers of all vehicles approaching the "GiveWay" line shall be able to see the full width ofthe circulatory carriageway to their left from the"Give Way" line for a distance appropriate to thesight stopping distance for the circulatory traffic(measured along the centreline of thecirculatory carriageway) as indicated in Table6.14, and shown in Figure 6.47. This alsoapplies to roundabouts that have parapet wallson either side of the circulatory carriageway.

This visibility shall be checked from the centreof the offside lane at a distance of 15m backfrom the "Give Way" line, as shown in Figure6.48. Checks shall be made that crossfalldesign or construction and sign location do notrestrict visibility.

It should be noted that excessive visibility atentry or visibility between adjacent entries canresult in approach and entry speeds greaterthan desirable for the junction geometry.Consideration shall be given to limiting inparticular the visibility of adjacent entries to thatfrom 15m back on the approach, and thevisibility along the approach to no more than thestopping sight distances for the design speed ofthe approach, by the selective use oflandscaping.

January 1997

SECTION 6

Forward Visibility at EntryDrivers of all vehicles approaching the "GiveWay" line shall be able to see the full width ofthe circulatory carriageway ahead of them for adistance (measured along the centre line of thecirculatory carriageway) appropriate to the sizeof the roundabout (as indicated in Table 6.14).The visibility shall be checked from the centre ofthe nearside lane at a distance of 15m backfrom the "Give Way" line as shown in Figure6.49.

Circulatory VisibilityDrivers of all vehicles circulating on aroundabout shall be able to see the full width ofthe circulatory carriageway ahead of them for adistance appropriate to the size of roundabout(as indicated in Table 6.14). This visibility shallbe checked from a point 2m in from the centralisland as shown in Figure 6.50. It is often usefulto improve the conspicuousness of centralislands by the use of landscaping, but this couldobstruct circulatory visibility. The circulatoryvisibility envelope will encroach onto the heightof vegetation or surface treatment. In thesesituations, limited penetration into the visibilityenvelope by vegetative growth of a dispersednature would not be unacceptable.

Inscribed Circle Diameter Visibility Distance(m) (m)

("a" in Figure 6.49)

<40 Whole Junction

40·60 40

60-100 50

> 100 70

Table 6.14 Visibility Distance

Pedestrian Crossing VisibilityDrivers of all vehicles approaching a pedestriancrossing across an entry shall have a minimumdistance of visibility to it of the Stopping SightDistance for the design speed of the link (seeSection 2). At the "Give Way" line, drivers of allvehicles shall be able to see the full width of apedestrian crossing across the next exit if thecrossing is within 50m of the roundabout (seeFigure 6.51). In urban areas, adjacent roadsidedevelopment may however prevent this visibilitysplay being fully established.

Page 6/47


Visual IntrusionsSigns, street furniture and planting shali not beplaced within the visibiiity enveiopes so as toobstruct visibiiity, but infringements by isolatedsiim projections such as lamp columns, signsupports or bridge columns can be ignoredprovided they are less than 550mm wide. Theonly exception to this will be positioning ofbollards on defiection islands and staggeredchevron boards on centrai isiands. Wherepossible, care shali be taken to minimise theeffects of pedestrians on visibility requirements.

January 1997

SECTION 6

Page 6/48


7 .3m Dual Carriageway

\\

\\

\-- ......-.L \...... ...... - - - ---=::.=-::::::::::::::::::::::::==-'E _ --- -

~ I -___ _--_-

"'T

11.3m Single Carriageway

7.3m Single Carriageway

a::::Il Vehicle Position Centre of Nearside Lanea Desirable Minimum Slopping Sight Distance (SSD) for Approach Road Design Speed

Figure 6.46 Measurement of Stopping Sight Distance



Area of circulatory carriageway overwhich visibility shall be obtained--':--/from viewpoint «3. Sight Stopping Distance for Circulating Trafficb. Half Lane Width

Figure 6.47 Visibility to the Left Required at Entry (From "Give Way" Line)

Area of circulatory carriageway over --"which visibility shall be obtainedfrom viewpoint <:{

<l. Sight Stopping Distance for Circulatlng Trafficb. Half Lane Widthc. Limit of Vl51bility Splay

Figure 6.48 Visibility to the Left Required at Entry (15m back from "Give Way" Line)

January 1997

SECTION 6

Page 6/50

Area of cirCUlatory carriageway over whichvisibility shall be obtained

from viewpoint »a. Sight Stopping Distance for Circulating Trafficb. Half Lane Width

c. Limit of Visibility Splay


Figure 6.49 Forward Visibility Required at Entry

Area of circulatory carriageway over whichvisibility shall be obtainedfrom viewpoint «

a Distance Related to CirCUlatory Speedb Limit of Visibility Splay

Figure 6.50 Circulatory Visibility

- -- - --

SECTION 6



<SOm

c---a-, :.'_-----;=-.Jlll1IL---7

'"

,\\\\\\ ,\ ,~/c/

/'~

I\\\\ ,

a Minimum area over which unobstructedvisibility Is required from viewpoint «when crossing Is within SOm of exit

b Half lane widthc Limit of visibility splay

Figure 6.51 Visibility Required at Entry to Pedestrian Crossing at Next Exit



6.10.11 Circulatory Carriageway

The circulatory carriageway should, if possible,be circular in plan, avoiding deceptively tightbends.

The width of the circulatory carriageway shallnot exceed 15m. However, block paving'collars' around the central island can be usedto provide additional width if long vehicle turningmovements need to be catered for on smallerroundabouts.

The width of the circulatory carriageway shall beconstant and lie between 1.0 and 1.2 times themaximum entry width. However, see Clause6.10.12 if small Inscribed Circle Diameters(ICDs) are being contemplated.

It is normal practice to avoid short lengths ofreverse curve between entry and adjacent exitsby linking these curves or joining them withstraights between the entry radius and the exitradius. One method is to increase the exitradius. However, where there is a considerabledistance between the entry and the next exit, asat three entry roundabouts, reverse curvaturemay result (see Figure 6.50).

There may be situations where the turningproportions are such that one section ofcirculatory carriageway will have a relatively lowflow. In this case, there may be an overprovision in circulating carriageway width andan area of carriageway, usually adjacent to anentry deflection island, becomes unused. Itwould be possible to reduce the circulatorycarriageway width by extending the deflectionisland and advancing the "Give Way" line. Thismethod of reducing circulatory width may alsobe adopted as an interim measure in the earlyyears of a scheme.

For larger roundabouts, this reduction incirculatory width can be achieved by the use ofhatch markings and is often associated withtaking out of use the offside entry lane. If suchmeasures are to be considered as an interimgeometric design feature for early years trafficflows, consideration should be given to the useof contrasting hard surfacing for these areas.

For smaller roundabouts it is more appropriateto consider interim circulatory carriagewayreduction by increasing the size of the centralisland. If this is to be introduced from theoutset, a preferable measure would be the useof contrasting hard surfacing but hatch markingscould also be considered.

January 1997

SECTION 6

6.10.12 Inscribed Circle Diameter (ICD)

The following advice is based on the sweptturning paths generated by a 16.5rn longarticulated vehicle with a single axle at the rearof the trailer. This is referred to below as the"Design Vehicle".

The turning width required by this type ofvehicle is greater than that for all other vehicleswithin the normal maximum dimensionspermitted in the classifications given in Table6.1, or likely to be permitted in the near future.The requirements for other vehicles (includinga 12m long rigid vehicle, 12m long coach, 20mdrawbar trailer combination, and a 16.5marticulated vehicle) are less onerous.

The smallest ICD for a normal roundabout thatwill accommodate the "Design Vehicle" is 28m.It should be noted that it may be difficult, if notimpossible, to meet the entry deflectionrequirement with normal roundabouts whichhave ICDs up to 40m. In this caseconsideration could be given to the installationof a low profile central island which wouldprovide adequate deflection for standardvehicles but allow overrun by the rear wheels ofarticulated vehicles and trailers. Such islandsshould have the same profile as the circulatorycarriageway with a maximum upstand of 50mm.

The turning space requirements for the "DesignVehicle" at normal roundabouts from 28m to36m ICD are shown in Figure 6.52. For ICDsabove these values, and/or where low profilecentral islands are to be installed, the circulatorycarriageway width should be checked againstTable 6.5. But usually the rule in Clause6.10.11 will provide more than adequate width.

6.10.13 Exits

The spacing of an exit and the preceding entryshall not be less than that which results from thecombination of the minimum entry radius (6m)and the minimum exit radius (20m), thoughdesirable radii of 20m, and 40m respectivelyshould be used where possible. If an existingroundabout is to be modified to include anadditional entry, care must be taken to ensurethat this does not affect safety at the proceedingentry and following exit. It may be necessary toredesign the whole junction if adequate spacingbetween adjacent entry/exit cannot beachieved.

The principle of "easy exits" shall be applied. Anearside kerb radius of about 40m at the mouthof the exit is desirable but for larger ruralroundabouts this may be increased to suit the

Page 6/53


overall junction geometry. In any case, thisradius shall not be below 20m or greater than200m.

At the beginning of an exit, its width, measurednormally to the exit radius, should, wherepossible, allow for an extra traffic lane over andabove that of the link downstream.

For example, if the downstream link is a single2 lane or wide single 2 lane carriageway, thewidth at the exit should be 7.0m or 7.5m, and ifthe link is a 2 lane dual carriageway, the widthshould be 10m to 11 m. This extra width shouldbe reduced on the nearside in such a way as toavoid exiting vehicles encroaching onto theentering carriageway at the end of the trafficdeflection island. Normally, this would be at ataper of 1:15 to 1:20, though where the exit ison an up gradient, the local widening may beextended to reduce intermittent congestion fromslow moving larger vehicles and to provide anovertaking opportunity for faster vehicles.Similarly, if the exit road is on a right handcurve, it may be necessary to extend the taperlength and the length of the traffic deflectionisland. Within single carriageway exits, aminimum width of 6m, measured normally to thenearside kerb, should be provided adjacent totraffic deflection islands to allow traffic to pass abroken down vehicle. Figure 6.53 shows atypical single carriageway exit embodying someof the above principles. On exits, the edge lineshould continue along the line of the kerbingonce this is terminated (see Figures 6.38 and6.39).

January 1997

SECTION 6

Page 6/54


\\\\\\I

IIIIII

I

/I

////..-.-',"

--------------_.......

a Main central islandb Low profile subsidiary central Island where providedC Remaining circulatory carriageway width 1.0-1.2 x maximum entry widthd Design vehiclee 1m clearance minimumf Inscribed circle diameter (ICD)

SECTION 6

Central Island Diameter R1 R2 Minimum ICD(m) (m) (m) (m)

4.0 3.0 13.0 28.0

6.0 4.0 13.4 28.8

6.0 5.0 13.9 29.8

10.0 6.0 14.4 30.8

12.0 7.0 15.0 32.0

14.0 6.0 15.6 33.2

16.0 9.0 16.3 34.6

18.0 10.0 17.0 36.0

Figure 6.52 Turning Widths for Smaller Normal Roundabouts



6.10.14 Crossfall and Longitudinal Gradient

Steep gradients should be avoided atroundabout approaches or flattened to amaximum of 2% before entry. Crossfall andlongitudinal gradient combine to provide thenecessary slope that will drain surface waterfrom the carriageway. Thus, although thefollowing clauses are for simplicity written interms of crossfall, the value and direction of thegreatest slope must always be taken intoaccount when considering drainage.Superelevation is arranged to assist vehicleswhen travelling round a curve. Its values, whenused, are equal to or greater than thosenecessary for surface water drainage.

Superelevation is not required on the circulatorycarriageways of roundabouts whereas crossfallis required to drain surface water. However, onthe approaches and exits superelevafion canassist drivers to negotiate the associatedcurves.

To provide comfort and enable drivers to remainin control, the maximum algebraic sum ofopposing crossfall gradients should not begreater than 5%.

a

a Exit Radius 40~100m

SECTION 6

Normal crossfall for drainage on roundaboutsshould not exceed 2% (1 in 50). Crossfallshould not exceed 2.5% (1 in 40). To avoidponding, longitudinal edge profiles should begraded at not less than 0.67% (1 in 150), with0.5% (1 in 200) considered the minimum.

The design gradients do not in themselvesensure satisfactory drainage, and therefore thecorrect siting and spacing of gullies is critical toefficient drainage.

For EntriesHere, curves may be tightened, (see paragraph6.10.9) and the degree of superelevation shouldbe appropriate to the speed of vehicles as theyapproach the roundabout but superelevationshould not exceed 5% (1 in 20). in cases wheresuperelevation is used, it should be reduced tothe crossfall required merely for drainage in thevicinity of the "Give Way" line, since withadequate advance signing and entry deflection,speeds on approaches should be reducing.

Figure 6.53

January 1997

Typical Single Carriageway Exit

Page 6/56


n/ ,

/ ,/ ,

a / , a/ ,

/ ,/ ,

/ ,/ ,

X t:>/

//

a //

//

//

Vb

~

a Crown Lineb Smooth Crown

Figure 6.54 Typical Example of Crossfall Design Using One Crown Line Which Joins the TrafficDeflection Islands by Straight Lines

For Circulatory CarriagewayValues of crossfall should be no greater thanthose required for drainage, although it is goodpractice at normal roundabouts, to arrange forcrossfall to assist vehicles. To do this, a crossline is formed where the entry and exitcarriageways meet the conflicting crossfall ofthe circulatory carriageway. This line can eitherjoin the end of the traffic deflection islands fromentry to exit (Figure 6.54), or divide thecirculatory carriageway in the proportion 2:1internal to external. The conflicting crossfalls atthe crown lines have a direct effect on drivercomfort and may also be a contributory factor inload shedding and large goods vehicle roll-overaccidents. The maximum recommendedalgebraic difference in crossfall is 5% althoughlesser values are desirable, particularly forroundabouts with smaller ICD. Care needs tobe taken during detailed design and at theconstruction stage to ensure a satisfactorycarriageway profile, without sharp changes incrossfall, is achieved. A smoothed crown isessential.

In some cases with small ICDs it may be moreappropriate to apply crossfall across the fullcirculatory carriageway width either towards the

central island or away from it. This should onlyapply where vehicle speeds are relatively low.

For ExitsSuperelevation, related to the horizontalalignment, should be provided where necessaryto assist vehicles to accelerate safely away fromthe roundabout. However, as with entries,crossfalls adjacent to the roundabout should bethose required for surface water drainage. If theexit leads into a left hand curve, superelevationshould not be introduced too quickly and tosuch a value that vehicles tend to encroach intoan adjacent (dual or opposing singlecarriageway) lane.

Adverse CrossfallAdverse Crossfall is crossfall that acts againstthe desired movement of a vehicle whenturning. It can lead to driver discomfort andeven safety hazards and should, if possible, beeliminated from the paths of the main trafficmovements at normal roundabouts. Smallernormal roundabouts in urban areas are oftensuperimposed upon existing pavement profilesand in these cases, the cross section of theexisting roads will influence crossfalls at theroundabout. T-Junctio'ns require particular



attention. Some adverse crossfall can beaccepted in order to fit the existing levelsprovided approach speeds are low. Limitedadverse crossfall at these roundabouts canassist in making the form of junction moreconspicuous to drivers.

6.10.15 Segregated Right Turning Lanes

Segregated right turn lanes are a useful methodfor giving an improved service to vehiclesintending to leave a roundabout at the first exitafter entry. Their use should be consideredwhen more than 50 percent of the entry flow, ormore that 300 vehicles per hour in the peakhours, turn right at the first exit. However, whenconsidering the use of these lanes, vehiclecomposition should be examined. If the rightturn vehicles are predominantly light and thereis a high proportion of cyclists and/or largegoods vehicles leaving the roundabout, therecould be problems with differential speeds atthe merge, particularly if this is on an uphillgradient. If segregated lanes are to be used inthese situations they should finish with a "GiveWay" line at the exit to the lane.

The use of these lanes in urban areas wherepedestrians are expected to cross should becarefully considered. In no circumstancesshould pedestrians be expected to cross rightturn lanes segregated by road markings.

If pedestrians are anticipated they should bechannelled with the use of guard rail to a safercrossing point. If this is not possible thesegregation should by a physical island ofsufficient width to accommodate the anticipatedpeak number of pedestrians.

There are two basic types of segregated rightturn lanes, namely segregation by roadmarkings and physical segregation. In bothtypes, vehicles are channelled into the righthand lane by lane arrows and road markingssupplemented by advance direction signs, andvehicles proceed to the first exit without havingto "Give Way" to others using the roundabout.Segregation by road markings is more common,but is less effective because it is subject toabuse. It is essential that the operation of thesegregated lane is not impaired by trafficqueuing to use the roundabout itself. Thedesigner should ensure that the approacharrangements are sufficiently clear so that theyare relatively self-enforcing.

Segregated right turn lanes should not inducehigh speeds. The design speed should notexceed that of either the entry or exit link, andany desirable speed reduction should beachieved at the entry to the lane rather than

January 1997

SECTION 6

within it. Forward visibility throughout thesegregated lane should be the appropriatestopping site distance for the design speed.Where the large goods vehicle proportion islow, the lane width may be reduced to 3.5m butshould not be less than 3.3m. Where roadmarkings are used to create the lanesegregation, the overall width of the markingshould normally be a minimum of 1.0m. Wherethe large goods vehicle content is higher, thelane width must be checked to ensure that itcan accommodate the swept paths of largervehicles, especially where physical segregationoccurs. Further information on the widening oflanes on curves is given in Table 6.5 andSection 3.

It is not necessary to make allowance forbroken down vehicles. With segregation byroad markings, such vehicles can be overtakenwith caution. Where physical segregation isintroduced, this should not prevent a right turnat the roundabout in the normal way from thenon-segregated part of the approach.

These lanes have been observed to handle1300 vehicles per hour with ease and for designpurposes a maximum capacity of 1800 lightvehicles per hour may be assumed where theexit is free running. Segregated lanes need notbe considered as part of the entry whencalCUlating capacities for other trafficmovements.

The merging between vehicles from asegregated right turn and other vehicles exitingthe roundabout should take place within 50m ofthe roundabout, where speeds are stillcomparatively low. Ideally, there should not bea forced merge. However, running the twostreams alongside each other is only possiblewhere the exit link can provide two lanes in thesame direction.

In other cases the segregated right turningtraffic has to merge with the other stream, givingway where necessary. This merging lengthshould be at least 10m long. Segregation byroad markings is not recommended if vehicleshave to give way at the merge point. Wherestreet furniture is placed on the island in thevicinity of the merge, it should not obstructvisibility.

In the improvement of an existing urban TJunctions, the signing on the segregated rightturning lane must clearly indicate to drivers thatthey have to "Give Way" to vehicles leaVing theroundabout.

Page 6/58


6.10.16 Road Markings

Road markings are used to channelize trafficand, where required, to indicate a dedicatedlane. Lane indication arrows to reinforce theadvance map type direction signs at entries canbe beneficial where heavy flows occur in aparticular direction.

Lane dedication by arrows and markings on thecirculatory carriageway is not normaliyrecommended. Where a roundabout isparticularly extensive and partially signalled andit is tending to a gyratory system, then somedegree of channelization by road markings mayprove beneficiai operationally.

January 1997

SECTION 6

Page 6/59


6.11 U-TURNS - GENERAL

Generaliy rural U-turns shouid be provided inadvance of or beyond junctions as foliows:

The provision of U-turn facilities are appropriateto a limited number of situations in rurallocations on duai carriageways and whencombined with other forms of junction in urbansituations. We shali consider rural U-turnfacilities only in this section.

•

•

•

•

Beyond a junction to enable drivers toreturn to an important junction if they misstheir turning

Beyond a junction to accommodate leftturn traffic movements not otherwisecatered for at the junction

In advance of a junction where throughand other turning movements would behampered by the U-turn movement

To facilitate maintenance operations, useby emergency services etc.

The area of median in the vicinity of the U-turnshould be kept uncluttered and free fromobstructions that are over 1.0m high and widerthan 500mm, with the exception of signs. Thevisibility requirements are given in Table 6.15.

This measure will help to ensure that driversexiting from the U-turn are able to see vehiclesapproaching from their right, and for them to beseen by drivers on the major road.

U-turns, in a similar fashion to left turns,contribute to congestion by drawing slowmoving turning traffic into the offside lane. Theyalso add to the accident hazard particularlywhere U-turning movements are heavy or ofslow moving vehicles. However, U-turns oftenafford the best economically available solutionto a given problem.

6.13 U-TURN ELEMENTS

6.13.1 General

The main elements in the production of anacceptable U-turn facility are:

One of the key requirements for a satisfactoryU-turn design is that the width of thecarriageway, including the shoulder or turningbay, be sufficient to permit the turn to be madewithout encroachment beyond the outer edgesof the road pavement. The minimum medianwidth for a U-turn is 11.6m. This aliows spacefor physical islands each side of traffic waiting toturn. U-Turns should be positioned at least400m in advance of or beyond any junction.Figure 6.55 illustrates the standard U-Turnlayout.

Wherever a U-turn facility is to be provided,consideration should be given to providing areciprocal U-turn. This enhances safety byreducing the likelihood of any illegal turningmovements that may have resulted from theprovision of a single U-turn facility and presentsa consistent layout to drivers.

6.12 SAFETY AT U-TURNS

Safety is a major concern at ali junctions,particularly on high volume, high speed roads.Where U-turn facilities are to be provided onthese roads, the hazard created by the turningvehicles and their interference' with throughtraffic must be minimised. Designs that enablevehicles to be in a protected position whilewaiting to turn are safest. As are those thatmake the turning vehicle cross and leave theopposing carriageway before returning to thenear side lane with a standard mergemovement.

January 1997

• Median width

• The length of the median opening

• Use of acceleration/deceleration lanes ortapers

• The nature of the turning traffic

• The design speed of the main road.

Figure 6.55 and Table 6.15 detail standard UTurn layout arrangements for rural locations.

6.13.2 Direct Taper Length (d)

The direct taper length is the length over whichthe width of a left turning lane is developed. Leftturning lanes shali be introduced by means of adirect taper whose length is part of thedeceleration length and depends on the designspeed. This taper length is given in Table 6.16.

6.13.3 Width of Physical Islands in theMedian

The width of median at the turning point shali bea minimum of 11.6m including hardstrips. Thiswidth is sufficient to shelter most large goodsvehicles using the U-turn facility. The minimumwidth of a physical island, usualiy located at theend of the direct taper shali be 305m. Theminimum width of physical island separating thestorage lane from the through lanes shali be1.2m or that necessary to incorporate signing.

Page 6/60


6.13.4 Left Turn Lane

The length of the left turning lane will dependon the major road design speed and thegradient. It consists of a median opening length,a storage/queuing length and a decelerationlength. The deceieration length shall beprovided in accordance with Table 6.17, inwhich the gradient is the average for the 50Omlength before the U-turn opening.

6.13.5 Median Openings (a)

The opening in the median at the crossing pointshall typically be 11 .Om Wide, as shown on Fig6.55. However this shOUld be adjusted to suitlong vehicles or those with abnormal loadswhen required.

6.13.6 Storage/Queuing Length (b)

The storage/queuing length shall be determinedin accordance with the requirements of theQatar Traffic Maunal. The queuing length shallbe separated from through traffic by a physicalisland on each side and the queuing lane widthshall be 5.0m.

6.13.7 Merging Length (e)

The merging length shall be constructed inaccordance with Clause 6.7.14. The mergelength commences a minimum distance of 45mfrom the inside radius of the median opening, orif the major road design speed is 120kph orgreater, the merge nose taper commences atthis point. The distance of 45m is that requiredfor the design vehicle to be parallel to the majorroad carriageway following the U-turnmovement.

The width of shoulder on the exit of the U-turnshail enable the design vehicle to make the Uturn without using excessive steering lock whilstmaintaining a 1m hardstrip from the outsidewheel to the edge of surfacing. To aid vehicledirection, the shoulder should be marked orstudded to guide vehicles to the merging length.

6.13.8 Pavement Construction

The pavement construction for the entire U-turnfacility shall be a minimum of that used for themajor through road construction. Whereconsistent heavy loading is expected, theengineer should consider more durablepavements. Refer to Section 9.

January 1997

SECTION 6

6.13.9 Road Lighting

It is particularly important that U-turns areclearly visible to through traffic. In all cases,street lighting shall be provided. Refer Section10.

6.13.10 Traffic Signs and Road Markings

U-turns shall be clearly signed in accordancewith the Qatar Traffic Manual. Considerationshould be given to providing additional signingfor the traffic on the through route to indicatethat vehicles may be crossing the road ahead.

6.13.11 Drainage and Crossfall

To allow for surface water drainage and drivercomfort, the road crossfall on the major roadshall be continued through the U-Turn. Checksshall be made for flat areas at all changes ingradient, superelevation or crossfall. Surfacerun-off shall not be allowed to collect in streamsand flow from the U-Turn across the majorthrough road, or to collect on or cross the UTurn lane so as to present a hazard to vehiclesmanoeuvring and braking. In addition, the ruralsituation requires the engineer to carefullyconsider the maintenance requirements of anydrainage system he adopts. Refer to Section8.

Page 6/61


ll. Median openingb. Queuing lengthc. Deceleration length + direct taper lengthd. Direct I..per lengthc. MergIng length (nose length when required)$1 and S2. Visibility distances

II b I· ' I d I~~,~..::::::::::::::::_---_::::::::::::::::--:::_::::-::-:~~ "mlo I . I

Figure 6.55 Typical U-Turn Layout

Design Speed S1 S2on Major Road (m) (m)

(kph)

0-45 50 5.045 - 60 75 7.560 - 80 125 10.0Over 80 175 10.0

Table 6.15 Visibility Distances

Design Speed Direct Taper Length(kph) (m)

50 560 570 1580 15100 25120 30140 35

Design Up Gradient Down GradientSpeed(kph) 0-4% Above 0-4% Above

4% 4%

50 25 25 25 2560 25 25 25 4070 40 25 40 5580 55 40 55 80100 80 55 80 110120 110 80 110 150140 150 110 150 200

Table 6.17 Deceleration Length - c (m) forDual Carriageways

Note. Roundmg shall be applied to the kerbllnes, typically50mR.

Table 6.16 Direct Taper Length - d


.. Providing satisfactory diverge/mergelengths

.. Siting diverges and merges away fromother junctions or traffic generation points(both on the major and service roads).

Figure 6.56 shows a diverge and merge for aservice road off an urban road of design speed100 kph or greater. The spaci~g of divergenose to merge nose is also fixed by the designconstraints of the facility. Major roadhardshoulders continue across the junction asa painted hatched marking.


6.14 URBAN ROAD - SERVICE ROADDIVERGE/MERGE

Service roads should be provided in the urbansituation where through traffic on a districtdistributor or higher classification road will besignificantly affected by traffic manoeuvres fromdevelopments lying adjacent to the throughroad. The function of the service road istherefore twofold:

.. Collects connecting minor roads andconcentrates the entrances and exits to alimited number of locations along themajor road, thereby allowing major roadtraffic to flow more freely

..SECTION 6

Avoiding long straight service roads

.. Provides road users with a saferenvironment adjacent to developments byseparation from higher speed throughtraffic.

Service roads typically run parallel to the majorroad. However, their vertical alignment is oftengoverned by a lower design speed and cantherefore be used to match threshold levels inexisting development situations.

Figure 6.57 shows a similar diverge and mergefor a service road off an urban road of designspeed 80 kph or greater but less than 100 kph.The spacing of diverge nose to merge nose forthis design speed is fixed by the designconstraints of the facility. Major roadhardshoulders are shown with 45' tapers atdistances, set backs and shy distances shown.

The minimum weaving length between mergesand diverges is given in Table 6.18.

Service roads should preferably be connectedto major roads using the major/minor junctionscriteria listed earlier in this Section. However,limited reservation space usually requires thejunction to connect at a skew to t[ie major road.This creates the following undesirable situationswhich the engineer should recognise inpreparing service road designs:

The above points can be mitigated to someextent by:

..

..

..

..

..

Angled diverge off the main carriagewayencourages high speed entry into theservice road and consequent danger toother service road users

Angled merge onto the main carriagewayrequires the driver to make use of hismirrors to effect a safe merge with majorroad through traffic.

Eliminating parking and providinguncluttered visibility in the area of mergesand diverges

Introducing a chicane type manoeuvre atthe entrance to a service road thereforeslowing traffic entering the service road

Increasing the conflict angle wherevehicles entering and vehicles using theservice road meet

Design MinimumSpeed Merge/Diverge(kph) distance

(m)

120 500100 41780 33370 29260 25050 208

Note. Junction spacings may only be reduced below theseminima on the express approval of CEO Roads.

Table 6.18 Minimum Merge/Diverge WeavingLength

The minimum weaving length in metresbetween successive Merge/Merge orDiverge/Diverge measured between the tips ofthe noses shall be:

Weaving Length (min) = 3.75V

Where V = design speed of main road (kph)

The distance given by the above formula maybe increased if the minimum requirements foreffective signing are provided.

Note: Service roads would generally be oneway in the same direction as the major road, themajor road always being a dual carriageway orminimum 11.3m wide single carriageway.

However, where space permits, a service roadmay be two way with normal T-junctionentry/exits onto the major road.



DecelerationLen th Y = 4.0m

(See Table 6.9).....Service RoadOne Way

Major Road

3m Shoulder

MergingLength

(See Tabie 6.10)

Service Road

I-_M-,a3,,"jm°u..r.§Rc!J0.Qa!!dlc!!~r:.._LL.L..L.t.~:'2Y~:3:::0:"==;;~Z;~Z22Z22Z_ ,zzzllllllll

• One Way

Y = 4.0m

Figure 6.56 Service Road Diverge/Merge for Speeds;, 100kph

One WayService Road

Deceleration

I 10 I Length I.. .... Dr

(See Table,6.9)

30'---Y=4.0m

Parking or Shoulder

Spaint Markr~ 15 "I____ _0~51

Merging Length(See Table 6.10)

I'" / "I'" 10 Dol Major Road

:..\/30'-------

3.0

Service Road

One WayY=4.0m

Figure 6.57 Service Road Diverge/Merge for Speeds;, 80 kph < 100 kph




6.15.1 Residential Areas

In urban areas and, in particular, withinresidential areas, where there is the likelihoodof pedestrians crossing the road and whereparking may be on-street, careful considerationis required at road junctions.

The most commonly used junction to accessdevelopments and the most appropriate is theT-Junction. There are two basic forms ofaccess layout.

In the first form, the major traffic flow is on thethrough route (eg. a local road with accessroads joining), as shown in Figure 6.58.

In the second form, shown in Figure 6.59, alltraffic is distributed to the residential accessroads. This is the preferred method of treatingaccess roads, as the short lengths of straight,combined with the turning movements requiredat the junction, serve to restrict vehicle speedsand the number of accesses onto and off themajor route.

SECTION 6

traffic flow, for drivers on the minor road to failto obey the priority signing and drive through thejunction, thereby creating a hazard to traffic onthe major road.

The preferred form of vehicular crossingmovement is the staggered crossroads.Wherever possible the offset should be to theleft so that vehicles making the crossmovement first turn left then right. This isdiscussed in Clause 6.2.3.

Roundabouts may be used at the junctions oflocal roads with local roads and of local roadswith access roads.

However, roundabouts are generally onlyrequired where the volume of traffic on theminor road approaches is of the same order asthat on the major road, and where the overalllevel of traffic is such that vehicles on the minorroad experience severe delay. If the residentialroad network is properly planned, this shouldnot occur.

6.15.2 Older Residential Areas

Many existing older residential areas in Qatarhave particular requirements. When consideringrecoristruction of these roads, the following shallbe noted:

• High parking requirement

• Street system of ill defined through-ways,crossroads and rat-runs

• Poor illumination.

• Highly variable threshold levels, oftenadjacent.

Figure 6.58 MUltiple Access Roads Joining aMajor Road

r-----c--,- - - - - - - - - - - - ,---------,

I-----SIC-----I

•

•

••

Narrow road reservations giving rise topoor visibility, especially at junctions

Poor utility records and poor utilitycondition

No existing surface water drainage

Existing development in low lying floodareas

Figure 6.59 Access Roads Concentrated Priorto Main Road Junciion

As already discussed in Clause 6.2.2, the useof 'simple' crossroads is not encouraged asthere is a tendency, particularly in areas of low

January 1997

Faced with this number of considerations, it isessential that the engineer carefully plan therevised road system to meet the requi rementsof the area. Traffic should be restricted fromareas where it is undesirable, rat-runs should beclosed, parking regulated and surface watereffectively collected. The following are typicalactions:

Page 6/65


• Close or partially close one or more legsof a crossroads

• Provision of a sign posted alternativecycle route away from a junction

••

Introduce parking at every opportunity

Close some minor access roads leadingInto the development from local or districtdistributors

• Grade separation (eg. in urban areas) bymeans of a footbridge or subway. Thiscould be combined for use by bothpedestrians and cyclists.

•

•

Identify areas such as schools, shops,mosques, etc that may require specificconsideration for parking or access

Introduce one-way systems whereappropriate

If provision of any of these is not possible, thengreater emphasis should be placed on safetywith carefully selected crossing places. Atroundabouts, where cyclists are always at risk,motorists should be made aware of theirpresence by road markings and signing,especially where segregated right turning lanesare used.

• Introduce traffic calming if required

• Introduce block paving as a road surfaceto identify areas where pedestrian trafficIs a dominant factor

Pedestrian requirements at major/minorjunctions including roundabouts should becarefully considered.

••

Introduce effective surface water removal

Consider utility requirements for futuredevelopments and reconstruction

Although it is preferable to provide separatepedestrian routes away from junctions, whereroad crossing widths are less and trafficmovements more predictable, this is rarelypractical.

6.15.3 Other Road Users

Many of the factors identified for olderresidential areas can be satisfactorily applied toany older area. Engineers should first identifythe area uses and needs and apply suitablesolutions to arrive at a well thought out, safeand useful environment.

The principle road users in Qatar are vehicles.However, it is important that the'engineer alsoconsiders the requirement~ of other users of theroad system, particularly cyclists andpedestrians, where major/minor junctionsincluding roundabouts present a particularhazard.

Suggested facilities for improved pedestriansafety at junctions are given below:

Provision of a minor road central refugeat an unmarked crossing place withdropped kerbs and tactile paving, if In abusy pedestrian area

Provision of a pedestrian crossing, with orwithout a central refuge. These shouldnot be of excessive length or angled tothe road

Provision of a subway or footbridge.

Provision of displaced controlledpedestrian crossings

•

•

•

•

Introduce street lighting.•

Measures to improve cyciist and pedestriansafety are described below:

• Provision of cycle lanes adjacent to therunning carriageway will go some waytoward protecting the cyclist. This laneshould be identified with the cycle lanemarking. At junctions the minor road"Stop" and "Give Way" lines should beset back out of the way of cyclists

• Provision of a displaced cycletrack/footpath for shared use bypedestrians and cyclists with uncontrolledor controlled crossings at junctions

At-grade pedestrian crossing points should notbe placed in the. mouth of the junction. Insteadthey should be located away from the mouthwhere the carriageway is relatively narrow. Inurban areas, with low pedestrian flows, it ispossible to provide a central refuge in thehatched area of a ghost island junction, thoughit is important to check for the design vehiclemovements.

If a crossing giVing pedestrians priority isprovided close to the entry/exit points of aroundabout the safety of pedestrians will becompromised and traffic operation problemsmay become evident with the roundabout.Where a crossing must be provided within thelayout of a roundabout, a non-signalized



pedestrian crossing is preferred. A signalizedpedestrian crossing may be confusing to driversapproaching the "Give Way" line of aroundabout. If a signalized pedestrian crossingis provided, it should preferably be of thedivided crossing type to minimise delays at theexits.

In urban areas, where iarge numbers ofpedestrians are present, pedestrian barrierswould prevent pedestrians from crossingindiscriminately across the junction. Theyshould direct the pedestrians to a controlled,safer place to cross. Pedestrian barriers shouldbe of the standard CED design and positionedso that the drivers view of the pedestrians ismaintained and vice-versa.

The type of safety facility seiected forpedestrians and cyclists at major/minorjunctions (including roundabouts) will dependupon the expected volume and movements ofpedestrians, cyclists and vehicular traffic.

January 1997

SECTION 6

Page 6/67


6.16 SIGNALIZED JUNCTIONS The lane width on the approach to the junctionshall be in accordance with Clause 5.2.

6.16.1 Introduction

6.16.2 Basic Requirements

When designing traffic signal installations, careshould be taken to ensure the following:

Reference shall be made to the Qatar TrafficManual and a concept layout should be agreedwith the Director of Civil EngineeringDepartment prior to proceeding with thepreliminary and detail design stages.

Design of signalized junctions brings togetherthe highway engineer and the traffic engineer.In Qatar this requires the close involvement ofthe Civil Engineering Department - RoadsDivision. The highway engineer is responsiblefor the geometric parameters of the road designon the approaches to and through the junction.The traffic engineer is responsible for thespecific layout of the junction in terms ofcapacity, turning movements, signing, marking,pedestrian considerations, specification andposition of signals.

It is preferable that left turn lanes and throughlanes are segregated by physical islands for theentire queuing length. It is also preferable thatentry and exit traffic on opposing carriagewaysis segregated by a median or physical island.

The number of lanes at the stop line shall bemaintained across the junction to the exit lanes.

If U-Turns are to be provided at the junction,lane widths and turning movements of differentvehicles should be considered and the positionof pedestrian refuge points checked againstpossible conflict.

Minimum visibility requirements to the primarysignals are detailed in the Qatar Traffic Manual.

The possibility of introducing slip roads at thecorners of a junction should always beconsidered. These allow right turning traffic to"Give Way" or "Stop" rather than wait for thesignals. They also provide larger turning radiithan would otherwise be the case and can bebeneficial to pedestrians when provided withclearly defined crossing points.

Drivers have sufficient advance warningto know exactly which direction to take atthe junction

•

• Drivers are guided into the intended laneor lanes by road markings

• Drivers have a clear view of the signals atthe junction itself

• The junction layout allows easy visualrecognition of correct exit lanes andrequired vehicle trajectory.

• Movement from "Stop" line to exit lane isa natural flowing movement and does notinterfere with other movements allowed atthe same time.

6.16.3 Typical Layout Features

It is impractical to deal with all possiblevariations of junctions. The various featuresmentioned is this clause may be considered formost situations.

The size of traffic islands and pedestrian refugesis important. Adequate clearance between thekerb and any street furniture is needed toprevent damage by vehicles having a lateraloverhang.



SECTION 7 INTERCHANGES c) To improve the alignment of a road

7.2.1 General

7.2 TYPES OF INTERCHANGE

The decision to provide an interchange and thetype and detailed design of an Interchange willbe specific to a particular site. The seiection ofthe most suitabie facility for a particular site andthe associated design parameters depend upona number of controliing factors which include:

SafetyRoad classification for the connectingroutesDesign speedTraffic volume and mixRequired junction capacityNumber of junction legsTopographyLand available, the type of land and itspresent useEconomicsLightingEnvironmental impactAccess to local communitiesPedestrians, farming and cyclists.

To standardise junction types whenupgrading a corridor to motorway status.

d)

It is important for the engineer to use the correctterminology. The principle definitions relating tograde separation are given below:

7.1 INTRODUCTION

Grade Separation: Removes conflicts arisingfrom an intersection by the provision of abridge.

Junction: The treatment of the road alignmentat the intersection to enable traffic to negotiatethe intersection in the defined manner.

For new roads with high predicted traffic fiows,consideration can be given to grade separation.Grade separation removes confiicts betweenthe major vehicle fiows thereby improving safetyand capacity of an intersection. For existing atgrade junctions, grade separation can also beconsidered to improve safety and capacity ifthese partlcuiar problems have been identified.

Intersection: The meeting point of two or moreroads.

Interchange: When grade separation is usedbut a connection is maintained between theroads, this combination of grade separation andjunctions is called an interchange.

Interchanges may be complex and includeextensive connecting roads and loops. They willonly be required for the highest range of trafficflows.

This section sets out the requirements for thedesign, layout and size of Interchanges. It isessential that the engineer produces safedesigns that provide adequate capacity.

Interchanges are generally required betweenprimary routes and between primary andsecondary routes although they may bepositioned at the intersection of any urban orru ral road. The major selection criteria arealways safety and capacity.

Safety is always the most important factorfollowed by capacity.

Layouts will vary for different locations. It isuniikely that the layout for one site could bedirectly applicable for another. The traffic andtopography are unlikely to be the same.However, it is desirable to standardise layoutsalong a particular route wherever possible toattempt to reduce confusion to drivers andthereby improve safety.

The two forms of Interchange consideredprovide a wide variety of types available to theengineer. These have been classified into thefollowing generic types for selection of the mostsuitable form:

Interchanges may be considered to improve anexisting junction for a number of differentreasons. For example:

a) To remove a hazardous main at-gradejunction in order to improve safety

Full Interchanges

Full interchanges combine grade separation ofmajor conflicts with slip or loop roads that beginand end with diverges and merges.

b) To eliminate traffic delays at a bottleneckcaused by the volume of crossing andturning traffic

Full cloverleaf interchangeDirectional interchange with variants3-leg junction types including trumpetsPartial cloverleaf.



Advantages:

A typical full cloverleaf interchange is shown inFigure 7.1. It is a 4 leg interchange whichprovides free flow movements for all traffic. Itcompletely eliminates all left turn conflicts.Inner loop/slips are provided for the 4 left turnmovements and outer loop/slips are providedfor the 4 right turn movements.

Compact Interchanges

Compact Interchanges combine gradeseparation of major conflicts with connectorroads that either begin or end with a form ofjunction other than a diverge or merge.

Diamond junctions and variantsRoundabouts and variantsHalf cloverleaf and variantsCompact 3 and 4 leg grade separation

Junctions and Weaving SectionsThe main aim of grade separation is to removethe conflicts between turning vehicles therebyimproving safety and capacity. Thereforeparticular attention must be paid to the design ofthose areas of an interchange where thisconflict cannot be removed.

a)

b)

c)

d)

All left turn movements are provided forwith one grade separated single structure

All traffic movements are free flowing

The interchange may be built in stages

Traffic signals are not required.Junctions are the areas of carriageway wheretraffic joins or ieaves the main road and are thelocations where accidents are most Iikeiy tooccur.

Disadvantages:

a) Requires large land take

On a single carriageway road the lengthbetween successive junctions is called thestagger distance. Refer to Section 6.

On a dual carriageway the distance betweenany combination of successive junctions iscalled a weaving section. This is the length ofcarriageway in which drivers change ianes inadvance of turning off the main road. Due tolane changing, weaving sections must becarefully designed in order to give driverssufficient time to make their manoeuvres safely.Refer to Clause 7.4.9.

7.2.2 Full Interchange

This form of interchange provides uninterruptedmovement for all turning traffic by the use ofinterchange links.

Full Cloverleaf Interchange

b)

c)

d)

e)

f)

g)

Weaving lengths on both routes aregreatly reduced. A collector distributorroad would help weaving by reducing thetraffic speed, but would increase thestructurai costs

Multiple merges and diverges complicatetraffic signing

Short deceleration lane lengths for innerloops

The design speed of the inner loops isgenerally low

Provision for U-turn movement isrestricted until fully constructed

Significant environmental impact due tothe size of the junction.

Trumpet JunctionsTrumpet junctions can be of varying forms.Typical layouts are shown in Figures 7.2 and7.3.

Advantages:

b) Only one structure is normally required

Figure 7.1 Full Cloverleaf Interchange

January 1997

a)

c)

The layouts generally provide a relativelyhigh speed semi-direct connection forlarge traffic flows

Successive merges and diverges areavoided therefore no weaving lengths arerequired

Page 7/2


f) Simple structures can be achieved

c) Single exit slip road simplifies signing

b) Economic landtake and low constructioncosts

RoundaboutFigure 7.5 DumbbellInterchange

Can improve capacity of the at-gradeintersection by providing extra lane widthat entry, segregated turning lanes andtraffic signals.

g)

d) No weaving lengths are required on themajor road

e) No acceleration or deceleration tapersrequired on or under structures

Disadvantages:

d) Possibility of traffic turning the wrong waydown slip roads

a) Lower capacity on the minor road due toleft turning movements

With the many turning movements at twolocations on the minor road, visibility andintervisibility is difficult

Many points of conflict on the minor roadincreasing the accident potential. Trafficsignals will help reduce conflict

b)

c)

e) Turning traffic from the primary route hasto stop at the secondary route with thepossible requirement of wider lanes forstorage capacity

Figure 7.6 Two BridgeInterchange

Advantages:

Roundabout

f) Little possibility of future expansion of thejunction.

a) The dumbbell roundabout is veryeconomic with a signal structure and verysmall landtake

d) Single exit slip roads simplify signing

Interchange with Roundabouts and VariantsInterchanges with roundabouts can provide amore flexible junction arrangement than adiamond interchange. The roundabout elementcan cater for varying turning volumes, therebyreducing the overall delay to vehicles incomparison with simple T-junction elements.They are particularly useful when there is alarge percentage of left turning traffic.

The two most common forms of roundaboutinterchange are the two bridge and thedumbbell type. The dumbbell type is the mosteconomic because of the single structure andreduced landtake, however the two bridge typeis safer for larger volumes of traffic. These areshown in Figures 7.5 and 7.6.

b)

c)

e)

f)

g)

The two bridge roundabout, although notso economic is safer with a less confined"Give Way" area

High standard merge and diverge can beprovided in advance and beyond thestructure

No weaving lengths are required on themajor route

No acceleration or deceleration tapers onor under structures

Simple structures can be achieved



Disadvantages:

h) Can improve capacity of two bridgeroundabout by providing extra lane widthat entry, segregated turning lanes andtraffic signals.

4th QUlldmnt

40m20m R40m

a) The efficiency of the roundabout relies ondrivers being aware of how roundaboutsoperate. Drivers must give way to trafficon the roundabout to their left and mustnot queue across the exits which wouldcause the roundabout to lock 2nd Quadrant

Compact 3 and 4 Leg Partial CloverleafInterchangesCompact partial cloverleaf intersections can beused in rural or urban locations. They aresimple, low speed versions of partial cloverleafswith the same advantages and disadvantagesexcept that they have smaller land take andlower cost. Typical compact partial cloverleafinterchanges are shown in Figures 7.7 and 7.8.

b) Difficult to enter large, two bridgeroundabouts if circulatory speeds arehigh. Figure 7.8 Variant of Compact Partial

Cloverleaf Interchange

The objectives of compact partial cloverleafsare as follows:

a) Provide a safe means of crossing a highspeed route

b) Reduce the environmental impact of fullinterchanges by providing a compactjunction layout

====Il=:---..;:=0::v,::=Z::=========lr=~==~~===== e) Provide a junction with minimal land take

lsI Quadraifnl ICompact JConnector -....,Road

4th Quadrant

c)

d)

f)

Regulate and maintain vehicle speed forminor route traffic through the junction ata level appropriate to the layoutstandards

Remove the left turn manoeuvres fromthe major route

Provide an operational, efficient junctionlayout.

3rd Quadrant

The only disadvantage is that high speed trafficon the major route will exit on a tight loopradius. Adequate advanced signing, goodvisibility and chevron signing at the exit pointwill reduce the safety hazard. If all suchjunctions along a primary route are the samethen drivers would be very aware of thetightness of all such loops and would adaptaccordingly.

Compact~Connector lRoad2nd Quadrant

Figure 7.7 Compact PartialInterchange

Cloverleaf

g) Provide an economic solution formodifying an existing junction to gradeseparation standards.

January 1997

It is only when there is inconsistency in thedesign standards and types of junctions thatdrivers are confused and safety iscompromised.

Page 7/5


7.3 SELECTION OF INTERCHANGE TYPE

7.3.1 General

This section outlines the design procedures forselecting a form of interchange most suitable fora particular location. The geometric design ofthe elements are covered in Clause 704. Aseries of preliminary designs shall be preparedfor comparison before final selection andproduction of a detailed design.

7.3.2 Traffic Flows and Design Year

The major factor influencing junction design issafety. However, for the road network to operateefficiently, new junctions must have sufficientcapacity. It is not possible to ensure at the timeof design that a new junction has sufficientcapacity indefinitely. Instead, new and improvedjunctions shall be designed on traffic levelspredicted to occur in the Design Year, typically20 years after the opening of the schemes, toensure that they are free of congestion for areasonable period.

Predicted traffic flows shall be based on theexisting, observed traffic flows growthed up tomodel the Design Year flows. All Junctions andInterchanges shall be designed using the peakhour flows. The use of peak hour flows willmodel the worst case for traffic congestion. Ofparticular ''l1portance to junction design is thevolume of traffic undertaking each turningmanoeuvre. All predicted traffic volumes andturning volumes for the Design Year shall beagreed with CED Roads.

7.3.3 Junction Spacing Within the Network

In deciding on the form of the interchange theengineer must consider the location within theoverall road network. The aim must be toproduce a consistent junction strategy acrossthe network that maximises safety. Guidance onthe junction strategy for a particular locationshall be sought from CED Roads.

SECTION 7

than the minimum weaving length as defined inClause 704.9.

7.3.4 Initial Information Requirements andDecisions

The following information must be collated toform the basis for the selection of the mostappropriate type of interchange for a particularlocation.

Required Information:

a) Define the classification of the roadsapproaching the intersection

b) Define the carriageway cross-section ofthe roads on each side

c) Define the design speed of the roads

d) Define the proposed opening year for thenew facility

e) Obtain the existing traffic volumes mustbe obtained for the peak hour and applygrowth factors.

f) Define the location of any constraints tothe scheme. These include landownership, existing and proposedutilities, planning constraints, topography,dry wadi courses, flood plains andground conditions.

g) Define the environmental constraints.These include proximity to dwellings,severance of communities, plants ofparticular importance, animal habitatsand reguiarly used animal tracks andmigration routes.

Having collated the above information, thefollowing decisions must be made beforefinalizing the form to be used.

Initial Decisions:

The minimum spacing of consec.utive junctionson a multi-lane road is defined in Clauses 6.104and 704.9, and is based on safety requirementsfor weaving movements. This minimum spacingwill also allow the design of effective trafficsigning and lighting schemes for each junction.These clearances shall be achieved betweenthe maximum extent of the consecutive mergesand diverges for each junction. In nocircumstances shall spacing between junctionsof consecutive interchanges be reduced lower

January 1997

a)

b)

c)

Agree the overall strategy with CEDRoads

Agree predicted traffic volumes andturning volumes with CED Roads

Decide which turning movements will beaccommodated

Page 7/6


The engineer must also consider:

d)

e)

Decide which movements will be givenpriority with grade separation and highgrade links, and which minor movementswill be accommodated by low-grade linksand junctions

Confirm horizontal and verticalclearances for structures.

g)

h)

i)

Provision for non-motorway traffic andnon-motor vehicle road users

Estimate of construction costs

Method of construction

m) Provision of safety fences and barriers.

Preliminary designs will be discussed with CEDRoads and approval granted before theengineer progresses to detailed design. Certainelements of the preliminary designs may needto be worked up into more detail at the requestof CED Roads to fully assess the relative meritsof the preliminary designs.

I) Lighting and signing principles

Method of maintenance

includingeffectsEnvironmentallandscaping

j)

k)

No fixed rules can be given for the selection dueto the multitude of criteria that must beconsidered. Each location will have differentgoverning criteria and it is for the engineer touse his experience to select the mostappropriate type for evaluation.

The type of facility must be selected beforepreliminary designs are prepared. The varioustypes of junction and their relative advantagesand disadvantages have also been discussed inSection 6. For a given location two or moretypes of facility may be worked up intopreliminary designs for evaluation.

7.3.5 Type of Interchange for PreliminaryDesign

Safety will always be the highest priority.However, adequate capacity is also important toreduce congestion and thereby improve safety.Refer to Section 6.3.

7.3.6 Preliminary Designs

Preliminary designs are prepared for alternativearrangements to assess suitability and relativecosts. The main elements of the facility must bedefined in sufficient detail and at a suitablescale to determine the landtake required.

The items to be defined in the preliminarydesign include:

a) Safety implications for road users andnon-road users

b) Number of lanes required for eachmovement

c) Radii of links and loops

d) Vertical and horizontal clearances forstructures and maximum carriagewaygradients

e) Lengths of ioop roads, slip roads andmerges and diverges

f) Lengths of weaving sections



7.4.1 Definitions

7.4 DESIGN ELEMENTS

Interchanges are made up of distinct elements,each serving different purposes. Anyonefacility may have any number of these elements.The detailed design of each of these separateelements is covered in this section. Forclarification, they are defined below:

Connector Road: The length of road that joinsmerges, diverges, "GiveWay" or "Stop" junctionswithin an interchange. Slip,Link and Loop roads aretypes of connector road.

Main Road:

Minor Road:

Merge:

Diverge:

Auxiliary Lane:

The carriageway orcarriageways that are givenpriority, generally by natureof carrying the highestvolume of traffic.

The carriageway orcarriageways that are notgiven priority, generally bynature of carrying iowvolumes of traffic.

The area of taperedcarriageway where trafficjoins the main road.

The area of taperedcarriageway where trafficleaves the main road.

An additional lane addedparallel to the main road andused in conjunction with amerge or diverge carryinghigher traffic volumes toprovide extra capacity.

Loop Road: A particular form ofconnector road where thecarriageway turns throughan angle of approximateiy270 0 in order toaccommodate the trafficmovement.

Weaving Section: The length of carriagewaybetween successivemerges and diverges wheretraffic changes lanes inorder to reach its chosenexit.

Physical Nose: The point where thecarriageway surfaces of themain line and the merge ordiverge separate.

Painted Nose: The length of chevronmarking from the physicalnose to the intersection ofthe merge or diverge withthe main road travelled way.

7.4.2 Design Speed

Design speeds for slip roads and link roads arerelated to the design speeds for the main roadas shown in Table 7.1.

Main Road Urban RuralDesign a) 120kph (a) 140kph

Speed b) 100kph (b) 120kph

Type of Link Slip Link SlipConnector Road Road Road Road

Road

Design a)1200r100 a) 70 a) 140 or 120 a) 80

Speed b)100orBO b)70 b)120or100 b) 80

Table 7.1 Design Speed for Link and SlipRoads

Link Road: A particular form ofconnector road that joinsdiverges and merges withina full Interchange to provideuninterrupted movement forturning traffic.

Slip Road: The iength of carriagewaybetween the end of themerge or diverge and the"Give Way" or "Stop" line onthe junction within theoverall interchange.

January 1997

Where two alternative design speeds areshown, the engineer may use the lower if it isconsidered that safety will not be compromised.Where transition curves are used betweendesign elements within the interchange, thetransition curve relating to the higher designspeed must be used. The appropriate StoppingSight Distance must always be used. Designspeeds on slip roads must not be reducedbelow the stated values as they terminate with"Stop" or "Give Way" junctions and wouldcompromise safety.

Page 7/8


7.4.3 Lane Provision and Capacity

Lane provision for the main road, slip roads, linkroads and loops shall be based on the agreedtraffic flows as defined in Clause 7.3.2. Forinterchanges, the minimum number of lanesprovided on any particular element of thejunction shall be based on 1600 vehicies perlane per hour. The number of ianes shall berounded up to the nearest whole number.

The engineer may wish to increase the laneprovision above the minimum defined above foroperational reasons. The 1600 figure is basedon UK acceptabie congestion standards for allpurpose roads and may not be suitable for alllocations in Qatar.

Lane provision for the main road or roadsthrough the junction shall not be less than theprovision either side of the junction except withthe approval of CEO Roads.

Where the minimum lane provision is one lane,the engineer may wish to add an extra lane toreduce the potential for problems with brokendown vehicles blocking the carriageway orrestricted space for maintenance. Any proposedchanges from the minimum lane provision shallbe agreed with CEO Roads.

For the majority of interchanges, the maximumnumber of lanes provided for connector roads,is likely to be two. If the lane provision for anyparticular connector road, is more than two, theengineer may have incorrectly defined which isthe main road and shall refer to CEO Roads forguidance.

7.4.4 Hard Shoulders and Edge Strips

W here hard shoulders or edge strips(Reference to Section 5.4 and 5.5) are providedon the main road either side of the interchange,they shall be continued through the interchange.For connector roads, the provision of hardshoulders or hard strips shall be in accordancewith Table 7.2.

On the main road, the hard shoulder or edgestrip shall continue immediately after thechevrons for the painted nose.

January 1997

SECTION 7

Provision on Main Road

Hard Shoulder Edge Strip

Slip Terminate hard Continue edge stripRoads shoulder opposite 10 10m before "Give

physical nose. way" or "Stop" lineReduce at 1:30 to1.0m edge strip.Terminate edgestrip 10m before"Give Way" or"SlOp" line

Link Jf both main roads If both main roadsRoads have hard have edge strips

shoulders, continue continue them alongthem along the link the link road.road. ff not,terminate hardshoulder oppositephysical nose.Reduce at 1:30 to1.0m edge strip.

Loops As link roads As link roads

Table 7.2 Provision of Hard Shoulders andEdge Strips on Connector Roads

7.4.5 Merges and Diverges at Interchanges

Within interchange areas, merges and divergesare the iocations where accidents are mostlikely to occur. It is essential for the engineer topay particular attention to their layout. Trafficshould be able to leave or join the main road assmoothly as possible. To this end, the speedsof traffic joining or leaving the main road mustbe similar to that on the main road. Accelerationor deceleration to the appropriate speed shouldtake place on the slip road or link road beforethe merge or after the diverge. The geometry ofthe carriageway or other conditions in thevicinity of the merge or diverge must notimpede this smooth flow. Queuing in the area ofthe merge or diverge must be avoided.

Two aiternative types of merge and divergeshall be used depending on the volumes oftraffic as defined in Clause 7.3.2. They are thestandard taper and the auxiliary lane layout.The auxiliary lane layout has an additional laneparallel to the main road to increase capacity ofthe merge or diverge taper.

To select a merge layout, hourly flows for themerge and the upstream mainline are insertedinto the nomograph Figure 7.9. Theintersection point of the merge and upstreammain line flows will fall within a segment of thenomograph from which the number of lanesrequired on the connector road, and need foran auxiliary lane are determined.

Page 7/9


To select a diverge layout, the procedure isrepeated using the hourly flows for the divergeand the downstream mainline, and thenomograph Figure 7.10. The mainline lanecapacity is based on a flow of 1600 veh/hour.

Generally the auxiliary lane layout is used inlocations with higher volumes of traffic. Theauxiliary lane shall be the same width as thenearside lane of the main road but may bereduced to a minimum width of 3.5m in urbanareas on approval of CED Roads.

Where the existing mainline lane capacity isalready at a maximum or where exceptionallylarge merge or diverge flows are expected,provision of a lane gain a lane drop may berequired. In these instances, the engineershould refer to the "Design Manual for Roadsand Bridges, Volume 6 Road Geometry, Section2 Junctions, Part I TD22192 Layout of GradeSeparated Junctions" and the merge anddiverge layouts should be agreed with CEDRoads.

The standard taper and the parallel taper mergeand diverge are shown in Figures 7.11, 7.12,7.13 and 7.14. The geometric parameters forsetting out are shown in Table 7.3 for mergesand Table 7.4 for diverges.

Stopping Sight Distance in accordance with thehigher design speed from the adjacent elementsshall be provided over the whole length of themerge or diverge

January 1997

SECTION 7

Page 7/10


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3000

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G 1500~.QLLQlen 1000~

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Lane 1 Lane 2

Upstream Mainline

Lane 3 Lane 4

I I I I I I I

o 1000 2000 3000 4000 5000 6000

Upstream Mainline Flow (Veh/hour)

A = Standard TaperB =Auxiliary Lane

Figure 7.9 Merge Design



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a

500

2000

2500

1000

1500

3000

Lane 1 Lane 2 Lane 3Downstream Mainline

Lane 4

I I I I I I I

a 1000 2000 3000 4000 5000 6000

A =Standard TaperB =Auxiliary Lane

Downstream Mainline Flow (Veh/hour)

Figure 7.10 Diverge Design



Road Class Length of entry Taper for min Painted nose Min auxiliary Length of aux lane pertaper (m) angle at length (m) lane length (m) lane provided (m)

(1 ) physical nose (3) (4) (5)(2)

Rural140 kph 205 1:40 115 230 75120 kph 150 1:30 85 190 55100 kph 130 1:25 75 160 55

Urban120 kph 130 1:25 75 160 55100 kph 95 1:15 50 125 4080 kph 75 1:12 40 100 40

Table 7.3 Geometric Parameters for Merges

Pointed PhysicalTaper NOBO Noao

(1) (3) (2)

:~~~~~-~------------------ -

Taper

(1)

Auxiliary Lane

(4)& (5)

PaintedNose

IS)

PhysicalNose

(2)

Figure 7.11 Standard Taper Merge Figure 7.12 Auxiliary Lane Merge

Road Class Length of exit Taper for Painted nose Min auxiliary Length of aux lane pertaper (m) min angle length (m) lane length (m) lane proVided (m)

at physical (4) (5) (6)1 lane 2 lane nose

(1 ) (2) (3)

Rural140 kph 170 185 1:15 80 200 75120 kph 150 150 1:15 70 170 55100 kph 130 130 1:15 70 150 55

Urban120 kph 130 130 1:15 70 150 55100 kph 95 110 1:15 50 125 4080 kph 75 90 1:12 40 100 40

Table 7.4 Geometric Parameters for Diverges

Physical PaintedNoso Nose(3) (4)

:

Taper(1) & (2)

Physical Palnll,ldNose Nose AuxllJary Lane Taper(3) I') (5)& (6) (1)& (2)

= ------------------------------ ---------

Figure 7.13 Standard Taper Diverge

January 1997

Figure 7.14 Auxiliary Lane Diverge

Page 7/13


7.5 OTHER DESIGN CONSIDERATIONS

7.5.1 Clearance and Headroom

Clearances and headroom shall be designed inaccordance with Clause 3.7 and 4.6. Theengineer shall seek guidance from CED Roadsto define if any additionai clearance orheadroom is required for specific structures toaccommodate abnormal load routes.

7.5.2 Superelevation

Superelevation and camber shall be designedin accordance with Clause 3.4. Specialconsideration shall be given to thesuperelevation on adjacent design elements.The engineer must ensure that the entirecarriageway will drain efficiently and that thereis minimal risk of long vehicles grounding atchanges of superelevation.

7.5.3 Safety Fencing

Safety fencing shall be provided at locationsdefined in Clause 5.15. Special considerationmust be given to measures at the physical noseof diverges. High speed vehicles crossing thepainted nose are at particular risk. The ends ofsafety barriers at these iocations must be givenspecial treatment to reduce the dangers ofhead-on impact. Consideration shall be given tothe provision of energy absorbing terminationsfor these locations.

Direction and warning signs for interchangesmay be large and possibiy gantry mounted.Consideration must be given to the protection ofisolated signs and gantry legs.

In addition to safety fencing designed tomitigate accidents, consideration should begiven to provision of safety fencing to preventillegal movements within the interchange.lIiegal movements across the verges betweenslip or link roads are highly dangerous to alltraffic and must be strongly discouraged.

7.5.4 Signing

Effective and clear signing is essential for thesafe operation of any junction. This isparticularly relevant to interchanges wherevehicle speed and traffic volumes are high.Signs at such junctions will be large andpossibly gantry mounted. Adequate clearancemust be provided for the large foundationsrequired.

January 1997

SECTION 7

Detailed guidance on signing is provided in theQatar Traffic Manual. As a general point, theengineer must consider signing requirements atthe preliminary design stage. At this stage theengineer can build in suitable locations andvisibility splays for the signs.

7.5.5 Lighting

Suitable roadway lighting greatly reduces thepotential for accidents throughout the roadnetwork. Lighting design is detailed in Section10. As with signing, the engineer must considerlighting requirements at the preliminary designstage. Lighting columns can have very largebases which may need special consideration.

7.5.6 Utilities

Information must be obtained from the UtilityAuthorities at an early stage of the design.Diversion or modification to existing orproposed equipment can have a major impacton the design and the cost of an interchange.Utility Authorities may require servicereservations to be provided through theinterchange to accommodate future equipmentnot yet detailed.

7.5.7 Emergency Vehicles

At the preliminary design stage the engineermust consider how emergency vehicles couldreach the scene of an incident, particularly if thecarriageway is blocked by other vehicles heldup by that incident. Provision of additionallateral clearances at structures could beconsidered along with emergency mediancrossovers with demountable safety fences.

7.5.8 Maintenance Provisions

Maintenance of the carriageway is an importantlong term objective for the network. Theengineer must consider the implications ofmaintenance strategies and traffic managementon the layout of the proposed interchange. Hemust ensure that the facility will be safe tomaintain and that turning movements can bereasonably accommodated whilst maintenanceis taking place.

7.5.9 Environmentallssues

Environmental issues shall be considered at thepreliminary stage. All reasonable efforts shall bemade to design out unacceptable environmentalimpacts. The remaining impacts shall bemitigated as far as reasonably practical.

Page 7/16


One main impact of interchanges is visualintrusion due to their size. Carefui landscapingcan reduce the impact of large structures aboveground level. A combination of hard and softlandscaping can usually achieve the bestresults. Materials in keeping with thesurroundings should be used, with carefulconsideration of colours, textures and styles. Inproposing soft landscaping, the engineHr mustconsider how it could be safely maintainedthroughout the year, including regular wQtering.

The design of hard and soft landscaping mustnot interfere with the operational requirementsof the facility. No landscaping features shallobstruct stopping sight distances, visibility ofsigns or the effectiveness of roadway lighting.

January 1997

SECTION 7

Page 7/17


SECTION 8 DRAINAGE

8.1 INTRODUCTION

Reduces the damaging affectof pore water build up in thepavement, formation orsubgrade

8.1.1 Functions of Highway Drainage

Construction of a highway shall not be allowedto increase the risk of flooding to properties.

The highway drainage system must therefore beconsidered as providing four primary functions,which due to land use constraints are usuallydealt with differently in urban and ruralsituations, namely:

The requirement for satisfactory road drainagehas a direct bearing on the ability to use theroad during and after a rainfall event, long-termserviceability of the road structure, provision ofan acceptable urban environment andminimising health risk caused by long termsurface ponding.

Concentrates flood water todischarge basins for easyremoval.

Prevents damage to property inflood prone areas

Prevents pavement weakeningdue to ingress of salt lensesfrom the lower subgrade layers.

Determine points of concentration,discharge and hydraulic controls,together with method of entry into andexit from the drainage system

Determine the requirement for theprovision of sub-surface drainage.

In the case of exceptional rainfallevents the road surface itself can beused as a storm carrier:

Select appropriate criteria on limits andfrequency of acceptable flooding

Determine the total amount and rate (0)of storm water run-off reaching the pointunder consideration

Minor SystemThe Roads Division is responsible for the designof the Minor System, nameiy the road drainage,comprising gullies, soakaways, connectingpipework and storage areas required prior todischarge into the Drainage Division Network.The highway drainage system shall bedesigned using parameters defined in thissection. The point of discharge and dischargeparameters listed below, will be provided by the

Drainage of highways is the joint responsibilityof the Civil Engineering Department's RoadsDivision and Drainage Division. Each Divisionhas defined responsibilities and procedureswhich shall be adhered to when designinghighway drainage. These are explained in thefollowing clauses.

8.1.2 Minor and Major Systems

..

..

..

The engineer shall undertake the followingminimum studies for each highway using thecriteria set out in the clauses in this section:

..

..

damage to theor embankment

Minimisespavementstructure

Reduces the danger ofstanding water to traffic

Minimises road impact on thenatural surface hydrology inrural areas.

Maintains the use of alltrafficked lanes

Minimises disruption to traffic

Reduces sediment build up atthe road side

Guides surface water run-off tosuitable discharge points

Reduces percolation into theroad structure.

Remove water percolating through thepavement, lower ground water andprevent capillary rise:

Guide surface water run-off safelyacross or under roadways:

Collect precipitation falling on thehighway reservation, adjacent sideroads and catchment and convey to asuitable outfall:

..

..

..



CEO Drainage Division:

Diameter of trunk sewerAllowable discharge volumeInvert level of trunk sewerLocation of trunk sewerAcceptable method of discharge intothe trunk sewer.

Major SystemCEO Drainage Division is responsible for theMajor System which comprises all the drainagecomponents beyond the agreed interface pointwith the minor system:

Trunk. surface water sewer networkSurface water pumping stationsGround water control networksSurface water storage retentionareas/tanks.

The preferred drainage method is by a positivesystem. However should this not be practicaldue to distance from a suitable discharge pointor economics, agreement to discharge water tothe ground or adjacent areas may be soughtfrom the Director of the Civil EngineeringDepartment.

8.2 DESIGN CRITERIA

8.2.1 Hydrological Data

Rainfall CharacterizationLong term rainfall records for Qatar commencedin 1962 and are recorded daily. together withother weather information, from a number oflocations by the Civil Aviation and MeteorologyDepartment of the Ministry of Communicationsand Transport.

Summaries of recorded data are issuedregulariy.

Qatar lies in an arid region and annual rainfallmay vary from 20mm to over 300mm perannum. Individual storms occasionally asintense as 124mm in a 24 hour period and54mm in a 3 hour period. have been recorded.Rainfall is therefore characterised by:

• High variability

• Severe thunderstorms of limitedgeographical extent.

January 1997

SECTION 8

For the purpose of highway drainage design thecountry shall be considered as haVing the samerainfall characteristics for all regions.

The Total Rainfall and Maximum Rainfall in 24hours data (Table 8.1a & b) provided from DohaInternational Airport Meteorological Stationprovides the longest available rainfall recordand shall be referred to for design purposes.However, a more onerous review may berequired in specific cases where flood damageto strategic highways' or property would besevere.

Intensity-Duration-FrequencyData regarding individual storm events in Qataris scarce and generally inadequate. However,statistical analysis and comparisons by anumber of researchers has established anintensity - duration - frequency relationshipwhich is generally found to stand comparisonwith Bahrain data and to some extent. theBilham FormUla. See Figure 8.1 a & b.

1=25.4 [(1.25 x TIN)"282 - O. 17T

WhereI = rainfall intensity (mm/h)T = duration of storm (hours)N = Probable number of

occurrences in 10 years

Run-off Coefficients (C)Typically. for densely built up areas. there is ahigh run-off for all rainfall intensities. However.as development becomes more sparse orground conditions more pervious the total runoff will reduce. Run-off is also affected by stormintensity.

Calculation of surface water run-off shall bemade using Figure 8.2 which gives values forrun-off coefficients which reflect the abovesituations.

Page 8/2


State of QatarMinistry of Communications & Transport

Department of Civil Aviation & Meteorology

Total Monthly Rainfall (mm)

Station: Doha International AirportLat: 25 15N Long: 51 34E Elevation: 11 metres

Year/Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Total

1962 0.0 0.0 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4

1963 0.0 0.0 0.0 1.5 106.4 0.0 0.0 0.0 0.0 0.0 5.6 1.5 115.0

1964 23.1 36.3 13.0 2.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 155.4 302.8

1965 5.0 1.2 0.0 68.1 0.0 0.0 0.0 0.0 0.0 0.0 13.0 0.0 87.3

1966 0.0 40.5 0.0 3.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 43.9

1967 0.0 2.0 3.3 13.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 19.2

1968 0.0 40.4 0.0 27.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 68.2

1969 101.8 0.2 0.0 15.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 117.1

1970 10.7 0.0 1.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 12.2

1971 0.6 5.8 0.0 6.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 15.0

1972 1.6 6.7 57.7 9.6 0.0 0.0 0.0 0.0 0.0 0.0 1.0 7.9 84.7

1973 22.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 22.2

1974 5.8 23.4 16.7 1.7 0.2 0.0 0.0 0.0 0.0 0.0 0.0 4.1 51.9

1975 31,3 46.3 1.1 1.8 Trace 0.0 0.0 0.0 0.0 0.0 0.0 4.4 64.9

1976 25.2 53.9 23.1 40.3 Trace 0.0 Trace 0.0 0.0 5.4 45.5 Trace 193.4

1977 41.4 17.9 0.5 2.3 0.0 0.0 0.0 0.0 0.0 17.3 5.1 3.1 90.6

1978 0.0 12.8 1.0 5.9 0.0 0.0 Trace 0.0 0.0 0.0 Trace Trace 19.7

1979 5.7 0.1 68.9 Trace Trace 0.0 0.0 0.0 0.0 Trace 0.0 27.2 101.9

1980 12.7 30.8 6.6 Trace 0.7 0.0 0.0 0.0 0.0 0.0 Trace Trace 50.6

1981 6.4 2.4 23.4 Trace 1.6 0.0 0.0 0.0 0.0 0.0 0.0 Trace \33.6

1982 2.7 16.7 102.3 2.1 0.0 0.0 0.0 0.0 Trace Trace 20.3 21.2 167.3

1983 8.0 5.4 46.2 6.9 0.9 0.0 0.0 0.7 0.0 0.0 0.0 Trace 68.1

1984 Trace Trace 23.5 Trace 0.2 0.0 0.0 0.0 0.0 0.0 0.0 17.2 40.9

1985 1.7 0.0 0.5 Trace Trace 0.0 0.0 Trace 0.0 0.0 Trace 7.5 9.7

1986 4.7 7.4 5.7 32.6 Trace 0.0 0.0 0.0 0.0 0.0 Trace 27.6 78.0


1988 6.8 130.5 2.7 12.8 0.0 0.0 Trace 0.0 0.0 0.0 0.0 Trace 152.8

1989 Trace 2.0 12.6 2.7 0.0 0.0 0.0 0.0 0.0 0.0 9.2 43.2 69.7

1990 10.7 13.7 0.6 4.6 Trace 0.0 0.0 0.0 0.0 0.0 0.0 0.0 29.6

1991 0.3 1.3 26.2 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.1 31.9

1992 8.7 26.8 1.9 2.9 0.1 0.0 0.0 0.0 0.0 12.2 0.0 50.6 103.2

1993 12.1 74.4 2.3 6.4 2.6 0.0 Trace 0.0 0.0 0.0 0.0 Trace 97.8

1994 0.1 0.5 25.6 3.9 8.6 0.0 0.0 Trace 0.0 Trace 0.0 Trace 38.7

1995 0.0 32.4 141.6 6.6 Trace 0.0 Trace 0.0 0.0 0.0 0.0 60.3 260.9

Mean 12.4 18.7 19.7 8.4 3.6 0.0 0.0 0.0 0.0 1.0 3.0 13.4 80.1

Total 420.2 636.4 668.8 285.2 121.3 0.0 Trace 0.7 Trace 34.9 102.7 454.7 2724.9

Table 8.1 a Total Rainfall - Doha International Airport 1962 - 1995(Data to be reviewed at regular intervals)



State of QatarMinistry of Communications & Transport

Depanmenl of Civil Aviation & Meteorology

Maximum Rainfall in 24 Hours (mm)

Station: Doha Inlernatlonal AirportLal: 25 15N Long: 51 34E

Year/Month JAN FEB MAR APR MAY JUN JU, AUG SEP OCT NOV DEC Year

1962 0.0 0.0 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

1963 0.0 0.0 0.0 0.9 64.0 0.0 0.0 0.0 0.0 0.0 5.6 1.5 64.0

1964 47.0 15.0 13.0 2.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 80.1 80.1

1965 3.0 0.6 0.0 30.0 0.0 0.0 0.0 0.0 0.0 0.0 13.0 0.0 30.0

1966 0.0 17.6 0.0 2.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 17.8

1967 0.0 1.5 1.5 6.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.1

1968 0.0 25.0 0.0 14.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 25.0

1969 58.0 0.2 0.0 6.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 58.0

1970 6.7 0.0 1.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.7

1971 0.6 5.B 0.0 7.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 7.4

1972 O.B 2.5 32.1 4.6 0.0 0.0 0.0 0.0 0.0 0.0 1.0 5.9 32.1

1973 15.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 15.0

1974 5.4 9.2 9.0 1.7 0.2 0.0 0.0 0.0 0.0 0.0 0.0 2.5 9.2

1975 20.2 29.3 1.1 1.3 Trace 0.0 0.0 0.0 0.0 0.0 0.0 2.7 29.3

1976 23.2 23.2 9.4 94.4 Trace 0.0 Trace 0.0 0.0 3.6 45.5 Trace 45.0

1977 10.0 17.9 0.5 2.0 0.0 0.0 0.0 0.0 0.0 17.3 6.1 3.1 17.9

1978 0.0 9.5 0.5 5.6 0.0 0.0 Trace 0.0 0.0 0.0 Trace Trace 9.5


1960 7.2 20.2 3.0 Trace 0.7 0.0 0.0 0.0 0.0 0.0 Trace Trace 20.2

1961 6.4 2.4 12.7 Trace 1.6 0.0 0.0 0.0 0.0 0.0 0.0 Trace 12.7

1982 1.6 9.9 40.1 2.1 0.0 0.0 0.0 0.0 Trace Trace 17.3 11.8 40.1

1963 6.0 4.1 17.5 5.0 0.9 0.0 0.0 Trace 0.0 0.0 0.0 Trace 17.5

1964 Trace Trace 15.2 Trace 0.2 0.0 0.0 0.0 0.0 0.0 0.0 16.2 16.2

1985 1.7 0.0 0.5 Trace Trace 0.0 0.0 Trace 0.0 0.0 Trace 3.B 3.B

1986 3.7 6.2 3.4 17.1 Trace 0.0 0.0 0.0 0.0 0.0 Trace 16.0 17.1


1988 4.1 41.3 2.3 6.7 0.0 0.0 Trace 0.0 0.0 0.0 0.0 Trace 41.3

1989 Trace 1.3 5.0 2.6 0.0 0.0 0.0 0.0 0.0 0.0 8.3 34.9 34.9

1990 7.5 6.B 0.6 2.3 Trace 0.0 0.0 0.0 0.0 0.0 0.0 0.0 7.5

1991 0.2 1.3 14.7 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.9 14.7

1992 3.0 20.5 1.6 1.2 0.1 0.0 0.0 0.0 0.0 12.2 0.0 32.7 32.7

1993 5.5 44.6 1.9 2.0 1.6 0.0 Trace 0.0 0.0 0.0 0.0 Trace 44.6

1994 0.1 0.5 B.B 2.0 B.6 0.0 0.0 Trace 0.0 Trace 0.0 Trace B.B

1995 0.0 12.0 58.2 3.1 Trace 0.0 Trace 0.0 0.0 0.0 0.0 38.6 58.2

Highest 58.0 44.6 58.2 34.4 64.0 0.0 Trace 0.7 Trace 17.3 45.0 80.1 80.1

Table 8.1 b Maximum Rainfall - Doha International Airport 1962 - 1995.(Data to be reviewed at regular intervals)



1/r

J14 J/ /

11 if/ 1/ I

/ II /'II

I I I! II/ 1/

VI/

/ 1/ / I/ / 1/V1/ j

/ // I / I I/ /oII)

N

o 0 0 0OlI)O II)N ~ ~

(4/WW) Al!sUalullleJu!e~

o

0N N

N

j j'"..c: ~

<'Il

EQ)

~ >- 00 c: II) II)-~ U)

"0.... 0

j j0 'Cc: Q)

0 a."" c:<'Il~

~

::l ::l-0 Q)

II) 0::0

0 0 0~ ~

j jN0

o

Figure 8.1 a Bilham Formula, Intensity - Duration - Frequency Chart (O-4h)



IJIf

/ / I1/11

/ / / / j/ / ///

// //j'/

-----~~~/

SECTION 8

a aC") N

(4/WW) AllsualUI neJuletJ

a

Figure 8.1 b Bilham Formula, Intensity - Duration - Frequency Chart (1-24h)



1.0

0.9

0.8

0.7

0

LLLL 0.60Z::Ja::LL0 0.5(/).....ZW

~LLLL 0.4W00

0.3

0.2

0.1

0.0

• -,0 IRoof Can rete, Surf cinQ

"'~ ••s Fully Built up

./ C\\'i .0. ROc .-I-

./ S~P'\3 \\'I.A~~~ ~

j....---"

~ Co --- ~J...-,I c·' f;'"0\ e~

,... l...----"0;,"V--:,.:,,~ V ./ ,0· t---

~r«lw'0,' t:lY ~ \\eo ~

/ [V ,"clP' ~~ .~'f:o. V/ ~,ISP .." ~ ~vv

/

1'7 ,i.<'.?< ,,'1/' ,,' .-

I / k-/ ~1f/: 0'" 6.0\\.....V

I 1/ ~.;,

/';. ,"' 'e>• , '"

I I ~ e;.'~oI .....00 '<'- 1>9 05"

/ / IV - ~V~~ 0~ p"/ V ~-a " c~

.~V"

/ ./ '" ~ ,,'"I I "',c;;-: ,,,,"I / / 0;,"

I I ./

I I / .//

I / VI / V

I V

I / // /

/I /

I1/

"II

o 10 20 30 40 50 60 70 Bo 90 100 110 120 130 140 150 160 170 180

RAINFALL INTENSITY (I) mm/h

Figure 8,2 Run-off Coefficients for Urban Catchments

January 1997 Page8n


Catchment Area (A)

RuralThe area to be considered shall incorporatetwo parts:

• The area of the road corridor subject todirect precipitation

At a chosen point the peak flow generallyoccurs at the instant all parts of the catchmentare contributing to the flow.

The Time of Concentration (Te) is defined asthe interval in time from the beginning of therainfall to the time when water from the mostremote part of the catchment reaches the pointunder consideration by the engineer.

WhereQ=2.78CIA

Reference to topographic mapping should bemade to assess the catchment area.

UrbanThe area to be considered shall incorporate twoparts:

WhereV = Mean velocity of flow (m/s)n = Manning's coefficient of

roughnessR = Hydraulic radius (metres)S = Slope (percent)

When considering short duration storms therainfall intensity changes rapidly with only asmall change in storm duration, (Figure 8.1 a).Therefore it is important that for small drainageareas an accurate assessment of Time ofConcentration is made. However, due to thenecessity for the surface to receive rainfall andreach a flowing condition the Time ofConcentration shall not be reduced to less than3 minutes.

Time of Concentration:

For easy reference, when preparing drainagecomputations to the Rational Method, theengineer may use the nomograph given inFigure 8.3.

Te = -LV

The Time of Concentration is a function of theaverage slope, length 'and roughness of thecatchment.

Te = Time of Concentration(seconds)

V = Mean velocity of flow (m/s)L = Length of flow path from the

point of consideration to thefurthest catchment extremity(metres)

Where

V= R;;S~

n

A number of equations have been developed forcomputation of the Time of Concentration forvarious methods of flood analysis. However, itis recommended that where the RationalMethod is employed, Manning's equation isused for the calculation of flow velocity ingutters, drainage channels or pipes.

Manning's Equation:

The additional adjacent area assessedby reference to the Development Plansand topographic mapping for the area.

The area of the road corridor subject todirect precipitation

Surface Run-off (Q)Highway drainage areas to be considered inQatar are typically less than 50 Hectares. Forthese areas surface run-off (Q litres/second)shall be calculated using the formula:

For areas larger than 50 Hectares, mostly ruralconditions, consideration should be given toassessment of run-off by a combination ofhistoric observation and generation of stormhydrographs. The method used shall beagreed with CEO.

•

C = Run-off coefficientI = Rainfall intensity (mm/h)A = Area (hectares)

Time of Concentration (Tc)The engineer wishing to size a drainage systemmust ascertain the peak rainfall run-off from thecatchment under consideration for thedesignated design storm return period.

•

• The broader naturai catchment areawithin which the road runs.Specifically, the effect the road mayhave on the natural surface and subsurface drainage of the area.

The additional area will be dependent onfactors such as intensity of development,provision of flood storage areas, andcontribution from adjacent roads anddevelopments.



Highway Situation Storm ReturnClassification Period

(years)

Primary Rural 1 in 50Urban 1 in 50

Secondary Rural 1 in 20Urban 1 in 20

Tertiary Rural 1 in 10Urban 1 in 10

Table 8.3 Design Return Period - PositiveSystem

Table 8.5 Design Return Period - NaturalSurface Run-off

Area Description Rainfall

Residential Areas & 12mm in 24 hoursMinor Roads

Major Roads & 18mm in 24 hoursCommercial Areas

Table 8.4 Design Total Rainfall - SoakawaySystem

Where a positive drainage system is notavailable and drainage is to soakaways, thenthe 24hrs total rainfall figures given in Table 8.4shall be used.

Highway Situation Storm ReturnClassification Period

(years)

Primary Rural 1 in 10Urban 1 in 10

Secondary Rural 1 in 5Urban 1 in 5

Tertiary Rural 1 in 2Urban 1 in 2

Where the highway is required to cross a watercourse, the acceptable frequency limits againstflooding and damage from natural watercourses given in Table 8.5 shall be maintained:

The run-off that a positive highway drainagesystem shall be designed for is determined bythe Time of Concentration and reference to theacceptable frequency limits provided for thedifferent highway classes in Table 8.3.

Special measures required In thiS range.

Table 8.2 Typical Permeability

The design of an economic surface waterdrainage system is related to the acceptable riskagainst flooding. Though Qatar is an aridcountry, when storms occur, the disruption anddamage caused can be considerable. However,to provide a complete, risk free, surface waterdrainage system would be prohibitivelyexpensive. The following Design Return Periodtables list the minimum storm return periods tobe used in the design of surface water systems.

Soil Type Permeability(m/s)

1Clean gravels

10,1

10-2

Clean sandsand sand~ 10~

gravel mixtures10~

Desiccated andfissured clays

Very fine 10-5

sands, silts andclayMsilt 10'laminate

. 10-7

1O-e

Unfissured clays and clay-silts(>20% clay) 10-9

10-10.

8.2.2 Design Return Period

Should geotechnicai data not be available thenreference to Table 8.2 and to records heid byCEO Roads and Drainage Divisions shouldassist the engineer. However, where existingrecords are used, this shouid be verified by sitepermeability testing during construction in orderto confirm the design values used.

Permeability (P)Permeability of the ground shall be determinedby in situ geotechnical testing as described inAppendix B of this manuaL

Ideally the permeability will be assessed at anumber of locations aiong a project site andsoakaway sizes optimised on the basis of thetest results.

The engineer may chose a reduced level of riskif a specific project requires this.



Table 8.6 Design Return Period - Areas

A number of important points need to beconsidered by the engineer utilising this method.

If an area forms a boundary with no naturaloutlet for surface run-off then higher acceptablefrequency limits may apply. CED DrainageDivision should be consulted further for advice.

• Catchments where the contributingarea does not increase uniformly withtime can produce erroneous results.

Storm hydrographs should be built up fromexisting known storm data. However, thisinformation is currently not widely available inQatar and hydrographs such as a UK summerstorm are considered generally equivalent toQatar storms and therefore suitable for use inhydrograph models.

Design of larger diameter piped systems shouldtake account of pipe storage and proprietarycomputer software models should be used atthe direction of CED Roads to optimize systemdesign.

Retention ponds, storage tanks and hydraulicrestrictors shall be modelled using methods asagreed with CED Roads.

Each gully shall be connected to an individualsoakaway, except at junctions where areas tobe drained are reduced due to gully/channelrequirements.

Soakaway DesignSoakaways should be considered for surfacewater drainage in areas where a positivesystem is not available or economics precludethe use of a positive system.

Hydrograph MethodsSuitable for larger urban catchments wherestorage in pipes and above ground becomessignificant, and for calculation of overland flowin larger rural catchments for the sizing ofculverts and retention ponds.

Soakaways shall be positioned in accordancewith the reservation cross-sections given inSection 5.

However, areas of high groundwater table shallnot be considered suitable for soakaways. Inthese areas positive systems shall be providedwith outfalls to EFA's, storage/retention tanks orpumping stations.

Where permeability has been accuratelyassessed with confidence and where its longterm availability through maintenance is withoutdoubt, then ground permeability can beconsidered within the design of the soakaway.In all other situations the soakaway shall beconsidered a storage chamber and shall becapable of storing the total rainfall requirementof Table 8.4, below carriageway formation level.

Care should be taken in selecting run-offcoefficients and rainfall intensities foruse in the equations.

• Simple to use

Larger catchments can provideconservative results, typically whenchosen pipe diameters exceed 600mm

•

•

If there is a requirement to utilise the road as astorm run-off carrier in the case of a majorrainfall event then advice regarding theacceptable frequency limits for individualsituations should be obtained from the CEDDrainage Division. This will typically reflectthose shown on Table 8.6.

8.2.3 Design Method

Surface water drainage design should besubmitted to the CED Roads Design Section forapproval as part of the project detail designreport. Detail design should utilise theinformation provided within this Design Manual.Basic design methods to be used are as follows:

Lloyd Davis Rational MethodSuitable for the majority of surface waterdrainage systems enVisaged in Qatar, ego Minorbranch connections to a major trunk sewerdesigned by others. The relevant storm andcatchment parameters given in this section areused to calculate surface water discharge flowsand the piped system is sized to suit these flows.

A standard calculation sheet to be completedand submitted with designs is given in Figure8.4.

Classification of Area Subject to Flood StormReturnPeriod

Hospital/Airport 1 in 100Industrial 1 in 50Prestigious Commercial 1 in 20Government Offices and Private Offices 1 in 20Residential &Light Commercial 1 in 10

January 1997 Page 8110


Soakaways can introduce localised subsidencedue to wash out of fines. As such, they shall notbe positioned under the carriageway, shoulder orparking area or within 5m of a structure (subjectto geotechnical advice).

Soakaways shall be sized and located so as notto introduce water to the pavement construction.

Soakaways should be constructed with a risingpiece to enable shallow utilities to pass abovethe main chamber.

In particular situations the engineer can considerlinking soakaways by pipe connections at invertor intermediate levels. However, he shouldensure that this is not going to merelyconcentrate the surface water at the road valleypoint.

Where the existence of a perched water tablehas been established by geotechnicalinvestigation, CED Drainage shall be consultedregarding the use of combinations of boreholesand soakaways to discharge to lower aquifers.It should be noted that in some areas loweraquifers may be under a piezometric head orutilised for potable water purposes.

When a road is reconstructed or a pipeddrainage system is installed in an existing road,the original soakaways are unlikely to be eitherefficient or undamaged by corrosion and willneed to be removed or renovated.

January 1997

SECTION 8

Page 8/11


1\ 1\

1\1\

1\

1\ 1\ 1\1\

1\ 1\ 1\

1\ 1\1\ 1\

1\ 1\

1\ 1\ 1\1\ 1\0

~o 0o 0

P., o~ ~r< r\}:: 1\ 1\ 1\

1\I~ 1\

<iJ 1\ 1\

1\

V

r>'

...

itt;~.~~

~

V

Figure 8.3 Time of Concentration - For Use with Rational Method

January 1997

ooo

00

'"

E0 S0N 0

....JLL

0 00 Z~ «

....J~W

0 >'" 0

LL0II-

0 <.9NZW....J

0~

'"

~~

c:~

EN ~

WU

'" «LL... ~

::J'" (j)

~W>

0 0~

....JW>«

0 ~N l-

LL0 0'"0 W... ::;];0

'" I-0<0

SECTION 8

Page 8/12

t.. J:!III <0::l c<: CilIII~

'"'<~ :..'" (f)

'" 0---l:3(f)ro:;:ro~

0row

cO·::J

003

"0C

§:o·:J

-n0

:3

'1JIIIto

C1l

~

'"

STORM SEWER DESIGN COMPUTATIONS

Location of Pipe Diff. in Length Pipe Velocity Time of Time of Rainfall Impermeable Area (Ha) Flow Pipe papaclly Flow Velocity Velocity FemarkLevel Slope Flow Conc. Intensity Dia !capacily Full

From To (m) (m) (m/s) (min) (min) (mm/h) Roads Cut Other Total (m'/s) (mm) (m'/s) Velocity (m/s)

"~:lJ::r:l5::r:

~om(f)

l5z:s:>zc:>,...

(f)mgoZex>


8.3 URBAN DRAINAGE 8.3.2 Urban Catchment

8.3.1 Introduction

Drainage of highways in urban areas of Qatar isachieved using the major and minor systemsdescribed in Clause 8.1.2 and constructed andmaintained by the CED Roads and DrainageDivisions.

Highway drainage shall be provided for allurban roads.

Rainfall falling within the catchment area shallbe collected and disposed of within the highwaylimits or to a designated outfall point. Surfacerun-off shall not be allowed to shed outside thehighway reservation unless to a specifieddischarge point. Surface water shall not beallowed to stand within the highway reservationfor an extended period of time so as to causepublic nuisance or a health hazard.

It is important that the highway drainagerequirements are established early in the designprocess to ensure that adequate reservationspace is provided and service utilities routed toavoid possible clashes, particularly withsoakaways. Refer to typical cross-sections inSection 5.

Drainage problems can often be alleviated bythe engineer considering the layout of the roadsystem and planning of a new development inharmony with the natural drainage of acatchment.

Urban development causes changes to the runoff process by both altering the route andsurface characteristics over which the run-offflows.

Highways form a part of the urban catchmentand the highway engineer must carefullyconsider adjacent development and itsdischarge points and Gharacteristics in order toaccurately assess the total catchment that maybe contributing to the highway drainage systemunder design.

The urban catchment provides the engineerwith further points for consideration; that ofavailability of discharge points for the collectedwater, and the environmental damage due toincreasing build up of pollutants washed into thehighway drainage system.

8.3.3 Positive Drainage

Positive drainage is preferred in all urbansituations. Water collected is piped orchannelled to a discharge point from whence itcan be collected and discharged away fromroads and developed areas.

Highway drainage by positive means involvesdischarging run-off to a point advised by theCED Drainage Division for onward transmissionby the Trunk Sewer System.

8.3.4 Drainage of the Carriageway

• Guide overland flow

• Isolate drainage catchments intomanageable sizes

The roadway can be used to provide thefollowing functions:

•

••

Increase the drainage path and hencetime of concentration

Provide additional flood storage area

Provide a drainage reservation to thearea discharge point.

Rain falling on the road surface builds up andpresents a hazard to vehicles both during andafter storms. It is therefore necessary toprovide drainage to the carriageway by acombination of transverse and longitUdinalgradients, shedding to water collection pointsand a distribution system.

Typical topography in urban areas of Qatar,where roads are kerbed, requires slackgradients to minimise the appearance of a rollercoaster road and reduce fill requirements. Theminimum gradient criteria to be used are givenbelow:

Open areas such as parks, school yards, carparks etc. can provide storage areas should thedrainage system be unable to cope with areasurface water run-off. Their location shouldtherefore be carefully chosen at the planningstage to make the best use of topography anddrainage constraints.

January 1997

• Transverse gradients of 2% areprovided as normal for drainage off thetravelled way to the channel

Page 8/14


Figure 8.5 Typical Detail of a Rolling CrownAcross a Single Carriageway

•

•

•

Minimum longitudinal gradients of 0.3%should be provided to drain the edge ofa travelled way to a discharge point

However, a desirable minimumlongitudinal gradient of 0.5% is to beprovided, where practical

Care shall be taken at junctions andareas of superelevation to ensure thatthe combination of transverse andlongitudinal fall does not create a flatzone in the carriageway

In particular cases, a rolling crown maybe used as an alternative tosuperelevating channel lines to avoidflat zones, Figure 8.5. The length of therolling crown is determined using thesame formula as that for applyingsuperelevation (refer to Clause 3.4).

~_-,r,------,Smooth crown

x-x

To maintain gully performance under theinfluence of wind borne debris and dust and toimprove collection under the effect of highrainfall intensity, it is preferred that gullies areconstructed as pairs.

Valley points of large catchments should belocated in areas where flooding would presentminimal hazard or disruption, or whereadditional water storage or dispersion isavailable. ie Emergency Flood Areas (EFA),parks and gardens, trunk storm sewers etc.

Gullies shall be linked to the disposal system,by piped connections.

The preferred minimum gradient for gullyconnections is 1%. However, gradients of 0.5%are acceptable should situations dictate.

Maximum gully connection length is 36m.Should longer lengths be required thenintermediate manholes or catchpits shall beincluded in the scheme to facilitate cleaning.

Utilities shall be located so as not to provide ahindrance to the drainage system installationand maintenance or increase the chance ofdamage during utility maintenance works.

Storm sewer design shall be in accordance withCED Roads and Drainage Divisions' designgUides and specifications. Storm sewers shallcater for the flows computed from the designcriteria in this Section and any additional flowsadvised by CED Roads or Drainage Divisions atthe project commencement.

Drainage collection points in urban areas shouldtypically be prOVided by gullies located alongthe channel or gutter. On gradients of 0.5% orless the flow of water to the gullies can be aidedby the use of channel blocks. Gully spacing isa function of grating size, road gradient andcrossfall and acceptable flow width at thechannel. Standard gully spacings and criteriaare given in Figure 8.6.

Where standard criteria do not apply, theengineer should consider reducing the gullyspacing or referring the specific case to moredetailed calculation procedures.

On roads with longitudinal falls, valley pointsshall be provided with double gullies to aidwater collection.



200

190

180

170

160

150

140

130

120

E

(') 110z0« 1000..(j)

>-...J 90...J::::>(')

80

70

60

50

40

30

20

10

0

NOTE

Graph depictsLongitudinal gradientat channel given as %- Flood width of 1.0m- Crossfall2%- Heavy Duty Grating

\

\ \\ \\ 1\\ \

\ 1\

\ 50~

\ ""1\ I~

\ 2~

'" "" ...........

\ 1'-"" ----"\ ~

~""" ...........---0.3% i'--

-----I--r-..r--

2 3 '" 4<D

'"

5 ",6<D

'"

7 8'"r--

9 10 11 12

Figure 8.6 Gully Spacing

January 1997

IMPERMEABLE WIDTH (m)

Page 8/16


8.3.5 Drainage of Medians, Footways andVerges

MediansMedians in urban areas are normally paved orlandscaped with planting. Paved medians shallbe sloped to shed run-off onto the adjacentcarriageway for collection by the carriagewaydrainage system. Landscaped areas inmedians shall be edged so as to prevent run-offfrom these areas taking soil and plant debrisonto the carriageway.

SECTION 8

They are to be used in situations where run-offfrom sizeable catchments would becometrapped at a valley point and consequentialflooding would cause damage to adjacentproperties or render a road impassable with noequal adjacent route available for detours.

Water should not be allowed to pond forextended periods so as to cause a healthhazard.

Emergency Flood Areas shall therefore beprOVided with:

FootwaysFootways shall normally be sloped at 2%towards the carriageway to shed run-off ontothe carriageway.

.. A location where water can be easilypumped by tanker or temporarypumping station.

Where new highways are to be constructed inareas of existing development, care must betaken to ensure road levels are set to allow thefootway to slope from the property threshold tothe carriageway. Areas of wide paving mayrequire sloping to additional collection pointsaway from the carriageway. These collectionpoints must be suitable for pedestrian traffic tocross without risk of injury and must be situatedso as not to be a hindrance to maintenanceaccess.

It is the duty of adjacent property owners toprevent significant run-off across the footway bythe introduction of collection channels. This isparticularly relevant in the case of polluting runoff such as from petrol station forecourts.

Collected water may be added to the highwaydrainage system once cleaned of grit, oil andother pollutants.

VergesVerges with hard landscaping shall be sloped toshed water towards the carriageway. Wheresoft landscaping is prOVided then it shall beedged and sloped to prevent run-off fromdepositing soil and plant debris onto theadjacent pedestrian or trafficked surfaces, orinto property thresholds. Areas of raisedplanting which incorporate drain holes shallincorporate a filter membrane to preventwashout of soil onto adjacent areas.

8.3.6 Emergency Flood Area (EFA)

Emergency Flood Areas are portions of land setaside, within or adjacent to the highway reserve,that are used for additional storage ofexceptional run-off generated by storms greaterthan those normally designed for.

January 1997

.. Borehole soakaways to aid discharge tothe ground water table, whereinvestigation has shown this isachievable.

.. Permanent surface water pumpingstation and rising main connected to thetrunk sewer system.

In order to make the best use of land indeveloped areas it is normal practice to designEFA's as sports fields, parks, playing fields, carparks etc.

EFA's that are not landscaped or utilised forother purposes have a tendency to collectrubbish and become an eyesore.

EFA's should be considered a potentialdrowning and disease hazard. Where possiblethey should be kept shallow and spread over alarge area. This helps evaporation anddissipation and presents a less deep waterhazard. Side slopes should be gentle to alloweasy exit and marker posts should be locatedaround the rim to identify the deeper area intimes of heavy flooding.

Prior to designing EFA's the prevailinggroundwater table should be ascertained toensure the excavation does not allow standingwater to remain. Soakaways or boreholes canbe constructed in the base of the EFA toencourage water dissipation.

Page 8/17


8.3.7 Maintenance Strategy 8.4.3 Drainage of the Carriageway

All highway drainage systems shall be designedwith future maintenance procedures beingconsidered.

Routine maintenance will be required due tobuild-up of wind blown debris and settledsediments in gutters, gullies and pits.

In order to reduce surface build up of rainfalland the consequent hazard to vehicles bothduring and after storms, it is necessary toprovide drainage to the carriageway by acombination of transverse and longitUdinalgradients shedding onto the verge and adjacentland:

8.4 RURAL DRAINAGE

8.4.1 Introduction

Drainage of highways in rural areas of Qatarcan be considered as two cases:

Exceptional maintenance should be limited bygood design and construction practices.

Transverse gradients of 2% areprovided as normal for drainage of thetravelled way.

•

• Longitudinal gradients are notconsidered for drainage purposes onunkerbed roads. However, care mustbe taken during the design ofsuperelevated sections to avoid flatzones in the carriageway.

In areas where carriageway edge run-off coulddamage verges or steep embankments thenedge kerbing or edge channels shall beprovided to collect water to discharge points.

8.4.4 Drainage of Medians and Verges

MediansMedians in rural areas would normally beunkerbed and unpaved.

Discharge points would include gullies andprecast channels.

Drainage of rainfall falling onto the roadand highway reservation

Drainage of natural overland flows.

•

CEO Drainage Division are the responsibleauthority for maintenance of the Trunk StormSewer System.

CEO Highway Maintenance Section are theresponsible authority for the maintenance of thehighway drainage system, including EFA's andstorage areas not in the Trunk Storm SewerSystem.

•Drainage of run-off from the road and highwayreservation shall normally be achieved byshedding onto adjacent land.

The median should be sloped away from thecarriageway to prevent run-off washing soildebris onto the road.

8.4.2 Rural Catchment

The engineer is not usually faced with theproblem of catching and dissipating rainfall as inurban situations, but is allowing run-off to flowgenerally unimpeded on its natural course.

Rural catchments are often extensive and canbuild considerable volumes of water in theirlower reaches during even moderate stormevents.

Where run-off is collected from long sections ofgradient, median outlets should be provided atwadi and valley points to prevent water pondingand flooding onto the carriageway. Alternativelythe median may be broken into individualcatchment segments and surface water allowedto percolate into the embankment or evaporate.Median ditches, if required, should have amaximum side slope of 1 in 6 and shall bedesigned such that water in the ditch cannotpercolate into the road construction, see Figure8.7.

Considerable care should be taken in assessingthe size, slope and surface characteristics of thecatchment (refer to Figure 8.2) and applying theappropriate design storm (refer to Table 8.5).

Where ditches are required to facilitatesubsurface drainage, it is important to ensurethat adequate outlets or storage volume isprovided.



J~

------.,If-' -"'M"'.dria"'n'----~______if----I slo I,2~.L

In areas of steep cutting, ditches should belocated so they are not filled with loose debrisfrom the cutting. In areas where natural surfacerun-off is high it may be necessary to install aditch setback from the top of cuttings to preventrainfall damaging the cutting face.

8.4.5 Natural Surface Drainage

Where a highway crosses a wadi, the wadicatchment characteristics, design storm andclass of road will determine the type of roadcrossing required. It is normal practice to allowrun-off even from small catchments, to crossunder the road so as to minimise disruption tothe natural surface flow.

Rainwater storage

~ "u17%17%" ~LJ

-P=j~:----",2.",5-'-I."I---'2",.5'------<:F+Ditch1profile SL column

typically

--"''''-~~~~T~O~PyOf=D~i~!C~h==:c;r-lJ~5~~8omclear~ge~~:~~:::§::::::-

Longitudinal Sectionon Centreline

Fig 8.7 Typical Median Ditch

Verges and DitchesVerges in rural areas shall be sloped to shedwater away from the carriageway.

At the back of the verge a shallow ditch may beprovided to both collect and transportcarriageway run-off and catch minor area runoff for transport to wadiis along the route.

The designer shall ensure that ditches are notlocated so they can introduce surface water tothe pavement construction. Normal practice isto ensure the ditch invert is a minimum of O.3mbelow the carriageway formation level at theouter edge of the carriageway.

CulvertsA culvert is a covered channel or pipeline usedto convey a watercourse under the road. Itconsists of an inlet, one or more barrels and anoutlet.

Typically, culvert barrels will be constructedfrom concrete or steel pipes or boxes. Inletsand outlets may be constructed with gabions,mattresses, stone pitching or concrete.

The hydraulic characteristics of a culvert arecomplex due to the number of flow conditionsthat can occur. The highway engineer shallconsult specialist literature in his design ofculverts and shall choose the most appropriateculvert for the specific purpose considering thefollowing general constraints:

Ditch dimensions and shape shall be designedfollowing consideration of its location andimpact on highway safety together with thefollowing hydraulic considerations:

•

•

Preferred minimUm pipe culvertdiameter 800mm

Minimum pipe culvert diameter 450mm

contributing catchmentappropriate storm durationgradientroughness coefficient of lining/surface

• Flooding against embankments isacceptable short term. Freeboard toedge of carriageway to be a minimumof O.5m for the design storm.

The engineer shall balance embankment heightwith culvert height to provide a satisfactorytechnical and economic solution.

In most cases it is expected that rural ditcheswill be unlined. Permissible depths of flow forunlined channels are given in Figure 8.8.

Shallow side ditches are not normally graded toproVide a fall but follow the road profile.

Ditch slopes should not present a significanthazard to traffic leaving the road during anaccident. Side slopes of 1 in 6 or shallowershould suffice for this.

• Embankment slopes of 1 in 6 or greaterdo not normally require protectionagainst washout due to short termponding. Long term ponding mayrequire embankment slopes of 1 in 10.



FordsWhere wadi flows are exceptionally high or theroad requires a low storm design return periodand is lightly trafficked, culverts may proveimpractical. The engineer may thereforeconsider incorporating a dry ford or vented dryford. In designing a dry ford, care must beexercised to ensure driver awareness of thepotential hazard. Guide posts should bepositioned adjacent to the carriageway to assisttraffic positioning and advance signing shouidbe used to indicate the dry ford to approachingdrivers.

Specific attention must be paid to minimisingscour and the prevention of carriagewaysurfacing and edge loss. Verges, medians andembankment slopes should be protected byimpervious layers or rock. Washout ofembankment fines should be prevented by theuse of filter layers or impermeable membranes.

January 1997

SECTION 8

Page 8/20


oCf)

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eft. Q.. '-10 0 WOCf)

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I

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Figure 8.8 Permissible Depths of Flow for Unlined Channels



8.5 JUNCTION DRAINAGE

8.5.1 Introduction

Effective drainage of the carriageway atjunctions is particularly necessary for tworeasons:

SECTION 8

Lightweight Glass Reinforced Concrete (GRC)embankment channels are easily installed toprevent washout of embankment slopes atareas of run-off concentration such as at kerbends.

8.5.2 Drainage at Junctions

• The need to retain surface grip toenable the safe stopping, starting andturning manoeuvres routinelyundertaken by vehicles at theseiocations.

Carriageway crossfalls and longitUdinalgradients at junctions are used to channelwater to collection points. The following areexamples of satisfactory crossfall layouts withtypical collection points:

The following criteria must be considered tosatisfy the above requirements:

T-Junctions (Figure 8.9)

• Constant camber maintained on majorroad

•

•

•

•

•

The need to maintain the traffic systemcapacity, particularly at major junctionsmakes it essential that flooding of lanesand reduction in junction capacity isavoided.

Satisfactory transverse gradients mustbe maintained, particularly on theapproach to "Stop" or "Give Way" lines

Longitudinal gradients must be carefullychosen to keep slack sections ofchannel to a minimum

Where slack gradients are unavoidablethe transverse gradient should be aminimum of 2%

Collection points must be carefully sitedto avoid ponding or run-off acrosscarriageways from one channel toanother

•

•

•

•

•

Longitudinal gradient on major roadmaintained across minor road throat

Longitudinal gradient maintained onminor road to major road channel line

Constant transverse gradient on minorroad maintained to radius tangentpoints

Gully positions chosen to prevent flowcrossing the minor road entry/exit.

It is preferred to maintain the majorcarriageway transverse gradientsthrough cross roads or small signalizedjunctions.

MAJOR ROAD

• Collection points must link to an easilymaintainable disposal system withadequate capacity.

Junctions should preferably be situated awayfrom valley points for large catchments toprevent flood concentration at these points.Locating junctions adjacent to trunk sewers orEFA's to provide additional drainage facilitiesshould also be considered.

Urban junctions should always be kerbed andare therefore drained by gullies to the disposalsystem.

Rural junctions would normally be kerbedhowever an economic collection and disposalmethod may be achieved by flush kerbs locatedat collection points with shallow lined channelsremoving the water to the adjacent ground.

January 1997

-}---------,t--------{---r?~

I,I MINOR ROAO

lEI GULLY I..... DIRECTION OF DRAINAGE

Figure 8.9 Typical Drainage at T-Junctions

Page 8/22


Large Signalized Junctions (Figure 8.10)

.. Transverse gradients to be maintainedat approach to "Stop" lines & pedestriancrossings

.. Longitudinal gradients to be satisfactoryto prevent a large flat area beingcreated at the intersection point

.. Transverse gradients on right turn slipsto provide superelevation

.. Valleys created in siips to haveadequate collection and disposal points

.. Additional guliies placed at collectionpoints serving a large surface area

.. Gully positions chosen to prevent flowcrossing carriageways.

Roundabouts (Figure 8.11)

.. Transverse gradients maintained atapproached to "Give Way" lines

.. Longitudinal gradients to continue to bemaintained on approaches anddepartures

.. Channel of central island to fall to onecollection point

.. Transverse gradients providesuperelevation for right turners or thosecirculating

.. Gullies positioned to prevent crosscarriageway run-off.

January 1997

SECTION 8

Page 8/23


--I

tIll! GULLY-.. DIRECTION OF DRAINAGE

ttl t t-- ~---;m - F~-+ --§=J- -'- /---, , , ,

Figure 8.10 Typical Drainage at Large Signalised Junction

• GULLY... DIRECTiON OF DRAINAGE

/ ,/ ,

/ " ,;f ,

t--- --+ +

'- ;f,

" /, /, /

-f-I

Figure 8.11 Typical Drainage at Roundabouts



8.6 SUBSURFACE DRAINAGE ..SECTION 8

Tidal coastal areas where the watertable varies close to the surface.

8.6.1 Introduction

Water can be introduced to the pavement by:

.. Capillary rise from groundwater nearthe formation.

Where these situations are present, subsurfacedrainage is required to prevent build up of porewater within the pavement, formation andsubgrade. Increase in pore water can weakenthe pavement by:

SubSUrface drainage is not normally detailed inQatar as it is rarely a problem. Low lying areasare normally filled prior to development to raisethem sufficiently above the groundwater table.Roads are generally constructed onembankments in areas of high groundwater asthey are usually subject to flood inundationduring storms.

Subsurface Drainage Methods8.6.2

Alternatively, in rural areas, the provision of sideditches can serve the dual function ofintercepting overland flow and aid in thelowering of groundwater local to the roadstructure.

High GroundwaterIn areas of existing developm~nt where high orrising groundwater is likely to bring moisture tothe formation level, a collection and disposalsystem shall be installed to lower the watertable.

It is preferred that a soils investigation isundertaken to assist in deciding the need forsubsurface drainage.

.. Construction of high embankments

.. Introduction of a granular capillarybreak layer below the formation.

Coastal AreasIn tidal coastal areas, sabkha is likely to bepresent as an indication of a high groundwatertable.

General Design ConsiderationThe highway engineer should consider theintroduction of water to the formation as likely tohappen due to annual rainfall and irrigation ofplants in the median and verges.

This is generally prevented by:

It is normal practice that this is performed by theinstallation of a perforated land drain below thecarriageway, together with a positive surfacewater drainage system. This would normally beundertaken by the CED Drainage Division aspart to the Trunk Sewer Network. In theselocations, soakaways shall not be used fordrainage.

In these situations capillary rise of up to 1.0mcan draw saline water up to the road formatioAievel, depositing salt lenses and increasing porepressure.

the(old

throughcourses

is therefore onlyin the following

drainagenecessary

High groundwater table at the formationdue to natural water table or seasonalponding

Washout of fines by movement of porewater

Rainfall permeatingwearing and basepavements)

Swelling in susceptible material,followed by shrinkage or drying out.

Rainfall permeating through the vergesand medians

Increase in salt content in pavementlayers and subsequent swelling due tocapillary rise when appreciablequantities of salt are present in thesUbgrade

Transferring loads to lower (weaker)sections of the pavement throughincrease in pore water pressure

Subsurfaceconsideredsituations:

..

..

..

..

..

..

..

.. Areas of existing development andrising groundwater levels

In most cases the dry granular nature of thetypical Qatar subgrade layers means the porepressure rise due to percolation is slight.



However, to provide an additional safety factoragainst this occurrence, the following measuresshould be considered:

• Slope the formation to drain away fromthe carriageway to the verge or median

• Avoid steps in the formation that couldlead to water concentration points

• Keep planting areas separated from thepavement construction to preventmoisture transfer

• Ensure planting area watering iseffectively controlled to prevent overwatering

• Utilise surface water drainage detailsthat will reduce the chance ofaccidental damage and maintenanceproblems

• Ensure soakaways do not introducewater to the pavement construction.

January 1997

SECTION 8

Page 8/26


SECTION 9 PAVEMENT DESIGN

9.1 INTRODUCTION

9.1.1 General

The pavement designs described in this manualreplace those given in the 1989 HighwayDesign Manual issued by the Civil EngineeringDepartment of the Ministry of Public Works.Unlike the previous designs, based on the roadhierarchy and a standard subgrade, the newdesigns described in this section are based onthe cumulative traffic over a definite design life(normally 20 years) and three subgradestrengths. The designs are set out in catalogueformat and the technical basis for these isdescribed in an Annex at the end of this section.

All materials, methods of construction andtolerance used for road pavements must be inaccordance with the Qatar ConstructionSpecification (QCS). The Civil EngineeringDepartment (CEO) laboratory should beconsulted during both the design andconstruction stages of any project to ensure thatthe latest material specifications are beingused.

The various types of pavement constructionsdescribed herein may be used for kerbed or unkerbed roads, in locations with or withoutpositive drainage. Any requirement for kerbingand drainage will depend upon the exact natureand location of the road - refer to Section 8.

9.1.2 Typical Pavement Structures

A typical flexible pavement structure is shown inFigure 9.1. It comprises a wearing course laidupon roadbase and sub-base layers, and thesubgrade.

The wearing course must provide a skidresistant running surface and should be bothcrack and rut resistant. However, due to itsexposure to the extremes of temperature andhigh wheel load shear stresses, the wearingcourse will probably deteriorate and requirereplacement before the rest of the pavement.Resurfacing is likely to be required at intervalsof approximately 6-8 years during the life of theroad.

The roadbase is the main structural layer of thepavement and may consist of either asphalticconcrete or granular material (gravel or crushedstone) for medium traffic levels, but onlyasphaltic concrete for high traffic levels. Itsthickness is determined by the amount of trafficwhich is expected during the design life.

January 1997

SECTION 9

The sub-base is a granular layer to support theroadbase and its thickness is determined by thestrength of the underlying subgrade. In additionto providing adequate support to the roadbase,the sub-base must be able to carry constructiontraffic without developing excessive ruts.

The subgrade is the top layer of the earthworksand depending on the road geometry, will beeither cut or fill.

In rigid pavements, the asphalt wearing courseand roadbase are replaced by a high qualityconcrete slab, with or without reinforcement.The sub-base is normally cement bound ratherthan just granUlar, to ensure a robust surface onwhich to erect side forms and joint assembliesand to minimise any pumping of fine materialthrough slab joints.

FleXible-composite pavements consist of acement bound roadbase with asphalt surfacing.As the cement bound material normally crackstransversely due to shrinkage and temperaturewarping, the surfacing must be thickened toprovide insulation, to reduce the temperaturegradient in the roadbase, and to prolong theperiod for crack development through thesurfacing.

In pre-cast block paving, the asphalt surfacingis replaced by a layer of concrete blocksbedded on a course of sand. This pavementtype is only used in areas of low speed traffic,typically in parking areas, or when a contrastingappearance is required for areas such asmedian strips.

9.1.3 Road Deterioration

Generally, pavements gradually deteriorate withtime under the influences of environment andtraffic. The environmental deterioration can takethe form of hardening of the bitumen in thesurfacing which can lead to excessivebrittleness and cracking, or to salt damage ofthin surfaced roads built on or with salt-richmaterials. Poorly designed or maintaineddrainage can lead to weakening of pavementlayers or the foundation which then deformsunder traffic loading. Traffic-relateddeterioration can take many forms including thedevelopment of ruts, general unevenness of theroad surface, with a consequent loss of ridingquality, and cracking which can lead to pop-outsand potholes.

Page 9/1


Formation

(Generally, asphalt concrete, Limestone aggregate 110 - 230mm thickdependant on traffic. For traffic less than 5 million standard axles,granular material can be used for part of this layer)

(Granular layer, varying between 100 and 200mmdepending on subgrade strength)

Sub-base

Subgrade (In-situ or imported, CBR >15%)

Wearing Course (40mm layer of asphalt concrete, Gabbro aggregate)

Roadbase~I~

",r -m "

, "'.9, , , ,'.' '.', , , ,, , ,, , , ,'.' Va'", , , ,, , ,, , , ,, , , ,

Figure 9.1 Typical Pavement Layers

Determining when a pavement has "failed" or isno longer providing the intended level of serviceis not simple. Generally the deterioration is veryslow and variable. Criteria for "failure" can beset such as rut depth, roughness, deflection oreven the level of maintenance expenditure ortotal quantity of patching.

Occasionally, major deterioration can occurover a relatively short period of time when, say,a low quality, moisture susceptible sub-basebecomes wet due to surface cracking or a risein groundwater level. However, distress at thesurface of the pavement does not necessarilyindicate the structural failure of the road.Surface cracking and rutting within the wearingcourse material may be treated without theneed for major structural maintenance, as themain structural layer of the road, the roadbase,could be completely undamaged.

9.1.4 Variability in Materials and RoadPerformance

Road pavement performance is a ve ry variableprocess due to a number of factors. Variationsin the thickness and quality of the pavementlayers and variations in the strength of thefoundation all contribute to this, even thoughmaterials may comply with the relevantspecifications. Also, uncontrolled factors suchas the long term ageing of the bitumen causevariations in performance.

The random nature of variations in each layershould ensure that most deficiencies inthickness or strength do not coincide, or very

rarely so. The importance of good practice inquarrying, material handling and stockpiling toensure this randomness and also to minimisevariations themselves cannot be overemphasised.

Sometimes a road fails to carry trafficsatisfactorily to the end of its design lifebecause the traffic is considerably greater thanpredicted. Proper axle load assessment andreliable traffic forecasting are essential toprevent this. However in some circumstancesthis is very difficult and either a generouscontingency will have to be provided or thetraffic and/or pavement regularly monitored sothat strengthening can be carried out before thepavement is seriously weakened.

9.2 TRAFFIC ASSESSMENT

9.2.1 Introduction

Pavement deterioration under trafficking is dueto both the magnitude of the wheel loads andthe number of times the load is applied. Forpavement design purposes, it is essential toconsider not only the number of vehicles thatwill use the road over the design life but alsothe axle loads of these vehicles. This is doneby converting each axle load to an equivalentnumber of "standard axles" of 80 kN using anempirical relationship and totalling these overthe life of the pavement. The conversion tostandard axles is described in more detail inClause 9.2.5. Light vehicles cause negligibledamage - an axle load of 10 kN (1 tonne) has adamaging effect of only 0.00024 standard axles



compared to the normal maximum axle load of130 kN (13 tonnes) which has the effect of 6.45standard 80 kN axies.

The pavement designs in this manuai areselected on the basis of the cumulative traffic tobe carried over the design life expressed instandard axles. The determination of thisnumber is done in three stages:

1 The traffic for each class of vehiclewhich is expected to use the proposedroad, both at opening and subsequentiyover the design life, must be forecast

2 The axle loading of each class ofvehicle over the life of the road must beestimated

3 The cumulative number of standardaxles to be carried over the design lifemust be caicuiated from stages 1 and2.

These stages are described below.

9.2.2 Design Life

The design life for the majority of pavementswill normally be 20 years. In this period itshouid not be necessary to either strengthen orreconstruct the pavement provided that thetraffic volume and axle loads have been asforecast. At the end of the design period thepavement should still have sufficient integrity toallow overlaying, rather than full reconstruction,to extend the life for further service. However,some surface deterioration, generally rutting orcracking, will occur in this period. The rutscouid be caused by slow or stationary vehicles(at junctions), high temperatures and over-richmixes (where the mix parameters have driftedto high bitumen or low voids within the specifiedlimits) and couid develop early in the pavementlife before the bitumen has aged and stiffened.Cracking will normally arise (after 10 years) asa result of ageing of the bitumen in the hightemperature environment. Depending on thestatus of the road and the extent and degree ofsurface deterioration, resurfacing by a thinoverlay (40mm) or inlay (planing off andreplacing the surfacing) may be necessarywithin the design life.

There may be situations where the future trafficloading may be very uncertain depending, say,on the siting or timing of some majordevelopment. In this case it may be prudent toconsider a shorter design period and makeprovision for possibie strengthening overiayswhen plans are more definite. The CED shouldbe consulted in cases where a design perioddifferent to 20 years appears appropriate.

January 1997

SECTION 9

At the end of the 20 year design period, thegreat majority of pavements will continue to beused, but will probably require strengthening.The precise works will be determined byevaluation as described in Clause 9.6, but willprobably take the form of an overlay of 50 to150mm, with or without planing the existingsurfacing. Outside urban areas, with minimalkerblng and ironware and generous shouldersor verges, a raised road surface will not presentany significant problems. However, in urbanareas or adjacent to and under over-bridges,raised surface levels coLlid be difficult orexpensive to accommodate. In these areas, anincreased initial pavement thickness wouldallow inlays to be used and thus avoid the needfor overlays and changes in level.

9.2.3 Traffic Forecasting

This is an uncertain process, particularly in acountry with a developing economy such asQatar. To forecast traffic growth, the followingthree traffic categories must be considered.Anyone of these could be dominant orinsignificant, depending on the site.

1 Normal traffic, which would pass alongthe route even If no new pavement wasprovided

2 Diverted traffic, which is attracted to theroute because of the improvedpavement

3 Development traffic, which arises fromeither planned or unplanneddevelopment along the road corridor.(The latter type is sometimes termedgenerated traffic).

Normal traffic can be assumed to continue togrow according to current trends, either as afixed number of vehicles per year or as a fixedpercentage of the current total. Diverted trafficcan be considered from an economicperspective. It can be assumed that all vehicleswhich would save either time or money byswitching from an existing route to the newpavement would choose to do so. Divertedtraffic is normally forecast to grow at the samerate as the traffic on the road from which it hasbeen diverted. The quantity' of planneddevelopment traffic can be estimated from thedetails of policy plans. The quantity ofunplanned development traffic, sometimescalled generated traffic, will be far more difficultto predict but will be influenced by theavailability of land for such development and byexperience from previous road projects.Allowance must also be made for theconstruction traffic which will be associated withboth types of development.

Page 9/3


Traffic forecasting must differentiate betweenlight, medium and heavy goods vehicles as theirgrowth rates may be different and theirpavement damaging effects are very different.Whilst most routes will have approximatelysimilar traffic in both directions over a period oftime, checks should be made for any directionaleffects.

•

be factored up to obtain 24 hour totais

The average of the six 24 hour counts(total or vehicle class) in each directionshould be considered to be the oneway Average Daily Traffic (total orvehicle class)

9.2.4 Traffic Counts

• Traffic counts are performed on sixconsecutive working days (excludingFridays), for both travel directions

Manual classified counts should be carried outusing the Qatar standard 16 classes indicatedin Table 9.1. In order to ensure that the ADTand composition percentages arerepresentative of the yearly traffic, the followingmethod is suggested:

Conventional traffic counts, to justify or togeometrically design a road project, are usuallybased on manual or automatic methods whereall vehicles are combined to produce a singleAverage Daily Traffic (ADT) figure. The ADT isdefined as the total annual traffic summed forboth directions and divided by 365. However,for pavement design purposes, it is essentialthat classified counts are carried out so that theheavy goods vehicles which cause most of thepavement damage can be clearly quantified.The counting process must yield separate ADTvalues for each vehicle class. Also, forpavement design it is the traffic in one directionor individual lane, rather than the two-way flow,which is of interest.

Class Type No. Wheels Average No.of (on each of Standard

Axles side of the Axles pervehicle) Vehicle

1B00Nf

3 Mini-bus 2 1+1 or 1+2 0.2- 0.5

4 Bus/Coach 2 f+2 0.7 - 5.0

5 P/U Truck 2 1+1 or 1+2 0.1-3.0

6 Riaid Lorrv 2 1+2 0.4-7.0

7 Riaid Lorrv 3 1+2+2 1.5·6.0

8 Arctic. LorN 3 1+2+2 0.6-10.0

9 Arctic. Lorrv 4 1+2+22 1.5·10.0

10 Arctic. Lorrv 5 1+2+222 2.5·7.0

11 Arctic. LorN 4 1+22+2 1.5·7.0

12 Arctic. Lorrv 5 1+22+22 2.0 - 7.0

13 Arctic. Lorry 6 1+22+222 1.5·7.0

14 Trailer 3 +2+22 2.0 - 7.0

15 Trailer 4 +22+22 2.0- 10.0

• On important road schemes, the sixday counts should be repeated severaltimes throughout the year to ensureaccuracy in the ADT values.

Nole. Refer also to Table 6.1

For example, axle loads of 5, 8, 10 and 13tonnes are equivalent to 0.14, 1.00, 2.26 and6.45 standard axles, respectively.

9.2.5 Standard Axles

For pavement design purposes the damagingeffect of vehicle axles is expressed in terms ofa "standard axle". This was originally definedas one carrying 18,000 Ib (8,160 kg), in theAASHTO road trial in the USA in 1956-8(Croney and Croney, 1991). Subsequently thisload has been rationalised in SI units to 80 kN(eqUivalent to 8,157 kg). In order to determinethe cumulative axle loads over the design life ofthe pavement, it is necessary to convert thenumbers of each class of heavy vehicles thatwill use the road, to an equivalent number of80kN standard axles. Axle loads are related tothe standard axle using the followingrelationship:

Standard Axles ~ (Axle Load(kg)/8157

Times of abnormal traffic activity shouldbe avoided such as public holidays, etc.

•

The requirement for counts of present traffic willdepend on the type of road project beingconsidered and the relative magnitude of thethree types of. traffic expected to use it.Forecasting normal and diverted traffic willrequire knowledge of the flows and vehiclecomposition on existing roads running parallelto, or in the vicinity of, the proposed road.Obviously, development traffic cannot becounted, but traffic resulting from planneddevelopment should be quantifiable if thegeneral details of the planned residential,commercial and industrial projects are known.For most roads it is likely that there will be somerelevant traffic data available but this willprobably have to be augmented or updated byfurther counts.

• During the six days at least two countsshould be for a full 24 hours. Thecount totals for the other days should

Table 9.1 - Qatar Standard Vehicle ClassesFor each vehicle class, a representative number



2. Determine the average daily onedirectional traffic flow for each class ofvehicle

In order to determine the cumulative "standardaxles" over the design life of the road, thefoilowing procedure should be followed;

1. Determine the daily traffic flow for eachclass of vehicle weighed using theresults of the traffic survey

4. Determine the mean equivalence factorfor each class of vehicle and for eachdirection from the results of the axleload survey

Cumulative9.2.6 Determination ofStandard Axles

For dual carriageways it should be assumedthat the slow lane will carry ail the heavyvehicles unless local experience indicatesotherwise or the one-way ADT traffic flowexceeds 13000 vehicles per day. In the lattercase 90% of the heavy traffic should beassumed to travel on the slow lane. All lanes ofthe carriageway should be designed for the slowlane traffic. Each carriageway can be designedfor a different number of standard axles.

5. The products of the cumulative onedirectional traffic flows for each class ofvehicle over the design life of the roadand the mean equivalence factor forthat class should then be calculatedand added together to give thecumulative "standard axle" loading foreach direction. The higher of the twodirectional values should then be usedfor design.

3. Make a forecast of the one-directionaltraffic flow for each class of vehicle todetermine the total traffic in each classthat will travel over each lane during thedesign life

speed of the vehicles, the transverse position ofthe vehicle wheel and the smoothness of theroad surface. In UK, trials of WIM systemshave shown substantial unexplained variationsin average vehicle loads between sites withsimilar traffic. Moderate errors in weightmeasurement will be converted to much largererrors in the equivalent standard axle values. IfWIM systems are used, it is stronglyrecommended that check weighing of a sampleof the heavy vehicles be carried out usingconventional weighbridges, either permanent orportable types. This is in addition to thecaiibration already mentioned.

need to be weighed and the average number ofstandard axies for that class determined. Thisis then 'appiied to ail the vehicles of that classfor the design period. The values can varyconsiderably depending on the proportions ofthe various vehicle classes and the degree ofloading. On some routes, the loading is verydirectional, eg the approach to a quarry mayhave similar vehicle flows in both directions, butempty lorries in one and fully laden in the other,hence axle load surveys are essential.

Axle loads can also be measured and countedby weigh in motion (WIM) systems. Theseinvolve the embedment of load sensitive stripsor pads, flush with the road surface, across thewheel path. These systems are very attractivebecause axle loads are measured whilevehicles travel at normal speeds. However,WIM systems require careful, regular calibrationand the measurements are affected by the

At present, Qatar has no legal iimits on eitheraxle or gross vehicle weights. A considerableamount of overloading, relative to the designedvehicle weights occurs. Local surveys havefound extreme cases of vehicles being loadedto nearly twice their designed gross vehicleweights. Overloading causes a big increase inwear to the pavement. In the case of a 5-axlearticulated truck, this can increase from about 4equivalent standard axles, for the designedweight iimit, to 160 for the overloaded case.Obviously, not all vehicles will be overloaded tothis degree, but the average number ofequivalent standard axles per vehicle for eachtraffic class wiil generaily be higher than inplaces where legal iimits, related to the vehicledesign, are imposed and enforced. Anindication of the likely range of average valuesfor Qatar in each of the classes is shown inTable 9.1. (Classes 1 and 2, consisting of cars,4-wheel drive vehicles, iight pick-ups and taxiscause negligible pavement damage and havebeen omitted.) The wide ranges are due to thevarying proportions of loaded, part loaded andempty vehicles and the extent of overloading.The mix will vary with vehicle class and route.

Axle load surveys, using portable weighbridges,should be carried out to determine the axle loaddistribution of a sample of the heavy vehicles inthe vicinity of the road. Data coilected fromthese surveys can then be used to calculate themean number of standard axles for a typicalvehicle in each class. These values can thenbe used in conjunction with traffic forecast todetermine the predicted cumulative standardaxles that the road will carry during its designlife. Alternatively, there may be data availablefrom the CEO, who should be consulted on theneed for specific load surveys.



However, the differences would have to be atleast 50% before pavement thicknesses werealtered significantly. In practice, the largestnumber of standard axles in either slow lanewould determine the design for all lanes.

9.2.7 Design Traffic Classes

Accurate calculations of cumulative traffic aredifficult to make due to inaccuracies in the trafficforecasts and average numbers of standardaxles for each vehicle type. Consequently thepavement designs are provided as a set ofdiscrete thicknesses for defined ranges of trafficrather than as a graph of thickness versuscumulative standard axles. Each range ofcumulative axles is termed a class and theseare summarised in Table 9.2, expressed inmillions of standard axles (msa). Forcomparison, the pavement classes used in theprevious design manual are also shown. Whenthe forecast number of axles is considered fairlyreliable, and is within 10% of one of t'le classboundaries, it is acceptable to use a designbased on the average of the adjacent classes.

Traffic Class T1 T2 T3 T. T5 T6

Design Traffic <1 1·2 2·5 5 10 20(msa)

10 20 50

Previous Tertia""Pavement

SecondarvClassification

Prima'"

Table 9.2 - Design Traffic Classes

9.3 PAVEMENT MATERIALS

9.3.1 Qatar Construction Specification(QCS)

The full details of the materials to be used inpavement construction and the subgrade aregiven in the QCS together with the applicabletest methods, based mainly on BritishStandards. Brief descriptions of these materialsare given below.

9.3.2 Subgrade

Qatar generally has high strength natural soilsconsisting of weathered limestone or sands.Historically, it has been possible to constructearthworks, or at least the upper layers, usingmaterial with a minimum soaked CaliforniaBearing Ratio (CBR) of 25% and the previouspavement designs were based solely on thisstrength. However it is becoming impractical orexpensive to always provide this standard. Insome locations, such as cuttings, a significantlyhigher strength of in situ subgrade is possible.

January 1997

SECTION 9

Accordingly, the present pavement designsinclude three classes of subgrade defined byCBR:

S1: > 15% and <25%S2: > 25% and < 50%83: > 50%

The CBR values are measured using the BS1377 method, on soaked subgrade samplesstatically compacted to 95% of the maximumdry density (MDD), determined using the BS1377 4.5 kg rammer method. There are alsograding and Atterberg Limit requirements,detailed in the QCS. The in situ subgrade mustalso be compacted to the same relativecompaction, namely 95% of MDD (4.5 kgrammer).

The specified subgrade strengths must besustained for a depth of at least 300mm and thematerial below this must have a CBR, at the insitu density, of at least 10%. This can be easilyconfirmed using a simple hand operatedDynamic Cone Penetrometer (Kleyn andSavage, 1982), rather than the much morelabourious method of recompacting laboratorysamples to the same density.

Where the above conditions are not fulfilled,either some of the subgrade material must bereplaced with higher quality material, or theamount of cover (fill height) increased. Thenecessary replacement or cover thickness canbe determined on the basis of providing thesame stiffness at formation level (top of theearthworks) as for the standard CBR 25%subgrade. Details for this procedure are givenin the Annex to this section. The proposals forthese non-standard subgrade situations must bediscussed with the CED.

9.3.3 Granular Material for Sub-base andRoadbase

The same material is used for both layers andmay consist of either crushed stone or gravel, ornatural gravel, or a mixture of these. There arerequirements for aggregate hardness, durability,cleanliness, grading, shape and strength, givenin the QCS. The principal requirement is for thematerial to achieve a CBR value of not less than60% when compacted to 100% of the maximumdry density (MDD) determined using the BS1377 4.5kg rammer method. This material isused as sub-base for all pavements, except theconcrete slab designs, in thicknesses rangingfrom 100 to 200mm, depending on subgradestrength. The in situ sub-base must becompacted to the same density as the CBR test,namely 100% of MDD (4.5 kg rammer).

Page 9/6


9.3.5 Cement Bound Material

9.3.4 Roadbase - Asphalt Concrete

9.3.6 Wearing Course

The criteria for compaction on the road willresult in average voids from 5 to 6 % in the laidmaterial before trafficking.

In order to reduce the risk of cracking due toimperfect curing or joint construction, reinforcedjointed slab construction has been adopted.LongitUdinal reinforcement to BS 4483 isrequired at the rate of 600mm2/m width. Thereinforcement also reduces the slab thicknesscompared to an un-reinforced slab and reducesthe number of transverse joints. Thereinforcement is placed with 50 to 60mm ofcover below the slab surface and maintaining aminimum cover of 30mm below any longitudinaljoint sealing groove. Longitudinal joints must beprovided to limit slab widths to less than 5.Omfor limestone aggregate. Most other aggregateswith higher coefficients of expansion must belimited to 4.0m. Transverse expansion andcontraction joints must be installed alternately at15m intervals and proper transitions providedbetween sections of concrete and asphaltconstruction. Details of these features, derivedfrom the UK Highway Construction Details(DoT, 1991), are provided in the QCS.

These are manufactured from Portland Cementconcrete in two thicknesses, 60 and 80mm.The thickness to be used depends on the levelof traffic. The average compressive strengthmust be not less than 40 N/mm2 and individualblocks not less than 35 N/mm2

• Otherrequirements, including preferred shapes anddimensional tolerances are given in QCS.

9.3.8 Precast Paving Blocks

The required grade of bitumen is 60/70 Pen witha binder content typically between 4.0 and5.0 %. Compaction requirements are the sameas for asphalt concrete roadbase and the laidmaterial should have voids of about 5 to 6 %before trafficking.

The paving blocks are laid on a compactedcourse of sand, normally in simple herring-bonebond. The laying course sand may be eithernatural sand or crushed rock fines, complyingwith the grading envelope in Table 9.3. Thesand is laid so that after compaction it forms alayer 30mm thick. After placement, the blocksare compacted using a Vibrating platecompactor and finally, sand is vibrated into thejoints.

Rigid construction is included for use in localareas with a high risk of rutting. It may beadopted more widely in the future. Concreteslab pavements require high quality concrete,sometimes termed pavement quality concrete(PQC), with a 28 day cube strength of 40N/mm2

•

High quality mix constituents, good qualitycontrol and thorough curing are necessary toensure that the required standard is achieved.

9.3.7 Concrete for Rigid Pavements

8 kN4mm3to 6 %60to 75 %.

Minimum Stability:Maximum Flow:Air Voids:Voids Filled with Bitumen:

The standard form of pavement constructionuses a type MD1 asphait concrete roadbasebetween 100 and 230mm thick depending ontraffic loading. This material must comply witha given grading envelope (maximum particlesize 37.5mm) and will be proportioned using theMarshall Design method to meet the followingcriteria:

This is used as sub-base in the concrete slabpavements and as roadbase in flexiblecomposite pavements. A fairly wide gradingenvelope is specified for the material which mayconsist of, any or all of, sand, gravel or crushedrock. This is mixed with cement either in-placeor in an off-road mixer. A modest cube strengthof 7.5 N/mm2 at 7 days, is specified.

This material has not previously been muchused in Qatar, but is now included for use assub-base for concrete slab pavements and itmay also provide a cheaper roadbase. Limitson grading, cleanliness and durability are givenin QCS. For both sub-base or roadbase use,this material must be compacted to 95% ofMDD (4.5 kg rammer).

The required grade of bitumen is 60/70 Penwith a binder content typically between 3.2 and5.0%. The QCS specifies additionalrequirements for particle shape, soundness,particle strength, water absorption and abrasionresistance.

A standard surfacing of MD4 asphalt concrete,laid as a 40mm course, is used on all flexibleand flexible-composite designs. The nominalmaximum aggregate size is 14mm and the mixproportions are determined in a similar mannerto the asphalt concrete road base, but with thefollowing difference. Imported gabbroaggregate must be used for the coarse fraction,to provide adequate skid resistance andresistance to polishing. This last requirementraises the cost of the material considerably, andjustifies the thickness of only 40mm.



Nominal % by mass passinosieve size

(mm) Laying Course Jointing SandSand

10 100 100

5 90-100 100

2.36 75-100 95-100

1.18 55-90 90-100

0.6 35-70 55-100

0.3 8-35 15-50

0.15 0-10 0-15

0.075 0-3 0-3

SECTION 9

These pavements do not satisfy conventionalanalytical strain criteria but have performedsatisfactorily in other areas of hightemperatures. The designs in Figure 9.3 arebased on those in Figure 9.2, but with some ofthe asphalt concrete thickness replaced bytwice this thickness of granular roadbase. Thisis in accordance with the structural numberconcept of the AASHTO design method (1993)in which the reduction in thickness of one layeris compensated by increasing another, inproportion to the material coefficients. In thisinstance the granular layer (CBR 60%) has acoefficient of 0.13 whilst the asphalt (stiffness1.0 GPa) has one of 0.26.

Table 9.3 - Sand Gradings for Block Paving9.4.4 Flexible-Composite

(Figure 9.4)Roadbase

Full details of the laying procedure are given inthe QCS, based on BS 6717, Part 3.

9.4 DESIGN CHARTS

9.4.1 General

The designs for the various types ofconstruction are presented as a series of charts,Figures 9.2 to 9.6. Knowing the subgrade class(refer Clause 9.3.2) and the traffic class (referClauses 9.2.6 and 9.2.7) the thicknesses of thelayers can be easily read for each pavementtype. Not all types of pavement are consideredappropriate for every traffic class.

Pavement construction should be constantacross all running lanes as the savings to bemade by reducing the roadbase thickness arenot great. In rural situations, where the hardshoulder/edge strip is not expected to haveheavy usage, its pavement thickness may bereduced. In urban areas, where parking isexpected, a reduction of the pavementconstruction for the hard shoulder is notrecommended.

The design requirements for stagedconstruction is dealt with in Clause 9.5.

9.4.2 Asphalt Concrete Roadbase(Figure 9.2)

This type of construction will suit all classes oftraffic and is similar to past pavement practice inQatar. The basis of these designs arediscussed in the Annex to this section.

9.4.3 Asphalt and Granular Roadbase(Figure 9.3)

This type of construction is restricted to roadsexpected to carry no more than 5 millionstandard axles and with only a small proportionof heavily loaded vehicles.

January 1997

This type of pavement has not previously beenused to any great extent in Qatar although it isvery common and successful In somecountries. The cement bound layer will cracktransversely soon after construction through acombination of drying shrinkage and thermalgradient warping. The successful performanceof this type of pavement depends on theshrinkage of the cement bound roadbase beingsmall and the asphalt roadbase being tolerantof the cracked roadbase. The low strength of7.5 N/mm2 and the use of limestone, with a lowcoefficient of thermai expansion, should resultin narrow roadbase cracks. The hightemperatures are likely to assist the asphaltsurfacing in resisting the development ofreflection cracks.

Thick asphalt surfacing will reduce thedevelopment of cracking by insulating thecement bound layer and reducing thetemperature gradient and warping stresses.

The material thicknesses shown in Figure 9.4are based on UK practice. However, it isprobable that the asphalt surfacing thicknesscould be reduced in future designs, after someexperience of satisfactory performance isobtained.

9.4.5 Reinforced Jointed Concrete Slabs(Figure 9.5)

Rutting of conventional asphalt pavements atthe approaches to junctions or at roundaboutsis a significant problem in Qatar. It results fromthe high ambient temperatures, inherentproperties of the asphalt concrete and high axleloads. Although it may be possible to reducedeformation by mix re-design, or by the use ofbitumen modifiers, there will be uncertaintyover performance and the increased stiffnessmay could cause other problems in later life.

Page 9/8


Concrete slab pavements at these problemlocations will provide guaranteed, rut-freeperformance. Concrete pavements requireconsiderable attention to mix quality, placement,joints and curing to be successful. Jointedreinforced concrete slab construction has beenselected in preference to un-reinforced slabs asthe reinforcement will provide more tolerance toany workmanship deficiencies and wiil alsoreduce the slab thickness and number of joints.

The designs shown are based on UK practice(DoT, 1994) which is based on the work ofMayhew and Harding (1987). The concrete slab(40 N/mm', 28 day cube strength) rests on acement bound sub-base (7.5 N/mm', 7 dayminimum cube strength). This is to ensure thatthere is a robust surface on which to erect sideforms and joint assemblies, and that pumping ofsub-base or subgrade fines through joints isminimised. Joint details and reinforcementaround openings shail be as shown in the UKHighway Construction Details, Series C (DoT,1993) or as specified by the CEO.

The UK un-reinforced slab designs agreeclosely with USA practice (Portland CementAssociation, 1984). It has not been possible todirectly verify the reinforced slab designs as thePortland Cement Association manual does notcover this type.

If properly constructed, concrete pavementsshould last longer than asphait pavements and';e cheaper to maintain because they should notrequire resurfacing or re-texturing for at least 30years. However the joints wiil probably requireperiodic resealing at 15 year intervals.

9.4.6 Precast Block Paving (Figure 9.6)

Block paving may be used for the constructionof car parks or parking bays, median strips andverges, laybys and access roads. Selection ofthe appropriate design will be on the basis ofboth total traffic and the incidence of heavyvehicles. Granular roadbase has been selectedas this will be a more practical material thanasphalt for working in smail areas, which wiiloften be the case with this type of roadwork. Inaddition, any fuel or oil spillage wiil not affect thestructural layers.

The designs are based on German practice(Roads and Traffic Research Association, 1986)and are only suitable for the stated levels andtypes of traffic. Where block paving is requiredfor locations with substantial numbers of heavyvehicles, such as ports or industrial areas, otherdesigns such as those of the British PortsAssociation (1994) should be used. Theproposed designs for such situations should bediscussed with CEO.

January 1997

SECTION 9

Page 9/9


40

250

150

300+ •...• .. .. 300+ · .".< .. 300+ ·.. .. ;.:." ". ... -. 300+ .' . 300+.' . · . .. ··. .....

40

250

100

· .· .300+ .....

300+.-......300+· ... • -w· .

CBR,greater than50%

Traffic Classes T1 T2 T3 T4 T5 T6

Standard Axles<1 1-2 2-5 10~20(millions) 5-10 20-50

Subgrade 40

Class S1250

CBR,greater than15% 200and lass than25%

300+

SubgradeClass 83

SubgradeCrass 52

CBR,greater than25%and les8 than50%

Layer definitions Notes

Wearing Course (Asphalt Concrete MD4)

Roadbase (Asphalt Concrete MD1)

Sub-base (Granular Material)

Subgrade (CBR at 95% of MOD(BS 1377, 4.5Kg rammer, soaked»

1. Standard Axles are 80 kN.

2. All thicknesses in milllmetres.

3. These diagrams afe expected to have the widestapplication and are similisr to the past practice.

4. Roadbasa thicknesses greater than 130mmshould be laid in two courses.

Figure 9.2 Asphalt Concrete Roadbase Designs



150

150

4090

100

120

4090

300+

.'." ., .

. ' ".• '", 300+, .. ' '., .

300+

CBR,greater than25%and less than50%

CBR,greater than50%

SubgradeClass 83


Standard Axles1-2 2-5 10-20 20-50(millions) , <1 5-10

Subgrade Not 40 Not Not Not

Class S1 Considered 90 Considered Considered ConsideredSuitable Suitable Suitable Suitable

CBR, 150greater than15% 200and less than25%

300+

SubgradeClass 82


Wearing Course (Asphalt Concrete MD4)1. Standard Axles are 80 kN.

2. All thicknesses in millimetres,

Upper Roadbase (Asphalt Concrete MD1)

Lower Roadbase (Granular Base Material)


3. These designs are only to be used when theproportion of goods vehicles, with equivalentstandard axles of 12 or more, does not exceed5% of all vehicles.

... .... .... Subgrade (CBR at 95% of MOD(BS 1377, 4.5Kg rammer, soaked))

Figure 9.3 Asphalt and Granular Roadbase Designs



100

270

40150

......,," ~.

"" 300+." ... '."

T5 T6

10-20 20-50

40150

270

200

300+

"',."<0 ••

: .. :" 300+.. ~ ...

T4

5-10

NotEconomic

T3

2-5

NotEconomic

1-2

T2

NotEconomic

<1

T1

NotEconomic

Standard Axles(millions)

SubgradeClass 52


Traffic Classes


SubgradeClass 81

SubgradeClass 83

CBR,greater than50%

40150

270

300+

3. The asphalt concrete inhibits thedevelopment of reflection cracking.

2. All thicknesses in millimetres.

Noles

1. Standard Axles are 80 kN.

Upper RoadbasB (Asphalt Concrete MD1)

Lower Roadbase (Cement-bound Materialcube strength of 7.5 N/mm 2 at 7 days)

Wearing Course (Asphalt Concrete MD4)

4. A low strength Cement-BoundSub-base (Granular Material) Malerial has been selected to

minimise reflection cracking.

SUbgrade (CBR at 95% of MDD(BS 1377, 4.5Kg rammer,soaked» 5. The cost of this form of construction

is similiar to Asphalt ConcreteRoadbase, but could vary dependingon local circumstances.

Layer definitions

Figure 9.4 Flexible-Composite Roadbase Designs




Standard Axles1-2 2-5 5-10 10-20 20-50(millions) <1

SUbgrade Not Not200Class S1 Economic Economic

CBR,150greater than

15%and less than25% 300+

SubgradeClass 82

Sameas 81

Sameas 81

Sameas 81

Sameas 81

CBR,greater than 25%and less than50%

SubgradeClass 83

Sameas 81

Sameas 81

Sameas 81

Sameas 81

CBR,greater than50%


3. Transverse joint spacing shall be not greaterthan 15m.

4. These pavement designs are intended for useat junctions or other areas with a high riskof rutting.

Cement-bound Sub-base(7.5 N/mm 2 cube strength at 7 days)

Subgrade (CBR at 95% of MDD(BS 1377, 4.5Kg rammer, soaked»

1. Standard Axles are 80 kN.Concrete Slab (40 N/mm~ cube strength at 28 dayswith 600 mm2/m of longitudinal reinforcement 2. All thicknesses in millimetres.to BS 4463)

5. The design given for Class T3/S1 provides theminimum construction thicknesses to be used.

Figure 9.5 Reinforced, Jointed Concrete Slab Designs



Traffic Classes

Standard Axles(millions

SubgradeClass 81


SubgradeClass 82

CBR,greater than 25%and less than50%

SUbgradeClass 83

CBR,greater than50%

Layer definitions

TO

<0.5

300+

T1

0.5 -1

8030

200

200

300+

8030

200

150

300+

8030

200

100· ..w._ ••.'O."~.: ~ 300+• •• w"· ..

Notes

1. Standard Axles are 80 kN.Precast blocks (60 or BOmm)

30mm sand laying course

Roadbase (Granular Material)


Subgrade (CBR at 95% of MDD(BS 1377, 4.5Kg rammer, soaked))

2. All thicknesses in miIHmetres.

3. TO Traffic Class includes residential roads andparking areas with minimal heavy vehicles.

4. T1 Traffic Class includes laybys, dualcarriageway median strips and areaswith appreciable heavy vehicles.

Figure 9.6 Precast Block Paving Designs



9.5 SPECIAL PAVEMENT SECTIONS

9.5.1 Staged Construction (Single LayerConstruction)

Sometimes it is appropriate not to construct thefull pavement thickness at one time for one ofthe following reasons:

.. A road may initially be required to carryonly limited traffic. After thecompletion of related development(other roads or industrial or residentialprojects) traffic volumes will increase

A new road may carry constructiontraffic in the first few years of its lifeand thereafter normal traffic. Theapplication of the wearing course couldbe delayed until after the constructiontraffic has ceased to avoid rutting ofthe final surfacing

.. An anticipated change to traffic flowpatterns may require extensivechanges to road markings.

Assessments should be made in each case ofthe traffic over the whole design life and in theinitial period. The sub-base would be designedfor the whole life but roadbase and surfacingwould be matched to the initial level of traffic.The balance of the asphalt would be added indue course.

Pavements for temporary roads can often beconstructed to lower standards thanconventional pavements because performanceexpectations will be lower (deeper ruts or morecracking will be tolerable). However, thefollowing should also be considered:

.. Design period may be veryunpredictable

.. Design traffic may also be veryunpredictable

.. Savings may not be very substantial.

9.6 PAVEMENT EVALUATION

9.6.1 Introduction

As the road network reaches maturity, there willbe fewer new roads to design but more existingpavements to rehabilitate. Increasinglypavement engineers will be required to evaluateexisting pavements and devise appropriateresurfacing or strengthening measures.Pavements deteriorate in different ways and atdifferent rates depending on traffic, pavementthickness, material quality, drainage etc. Thevisible deterioration does not always give areliable indication of the underlying cause(s)and some investigation is needed. A fourstage, highway pavement evaluation procedureis outlined below:

However, other factors must also beconsidered:

9.6.2 Routine Monitoring

4. Interpretation and Remedial WorksDesign.

3. Detailed Investigation (Planning,Execution and Interpretation)

Routine Monitoring

Detailed Survey

1.

The objective of routine monitoring is to identifythose parts of the road network which areshowing signs of surface or structuraldeterioration and require further investigationand possible maintenance. Routine monitoringof most of the network should be carried out atintervals of 2 to 4 years, depending on the age,condition and importance of the road, and thetraffic usage. The monitoring will be by visualsurveys with written records of the conditionsupplemented by photographs or video tapes.Some indicative rut measurements should bemade. In rural areas the survey will normally becarried out during a slow (20 kph) drive-through,with occasional examinations on foot atjunctions, structures or any locations withserious defects. In urban areas the surveys will

2.

The approaches to underbridgesshould be constructed to full thicknessto avoid either overlaying the structureor full depth reconstruction of theapproaches.

Sufficient overbridge headroom mustbe provided to allow for the overlaythickness

Depending on the status of the road,the initial top course of asphalt mayhave to be a conventional wearingcourse containing gabbro aggregate.This will involve extra cost to providetwo, rather than one, asphalt courseswith superior aggregate

Kerbing, if present, must either beinstalled high or also raised when theoverlay is applied

Any ironware in the carriageway willhave to be lifted when the overlay isapplied

..

..

..

..

..



be carried out mainly on foot, from the vergesor footways. The results of all RoutineMonitoring should be stored in the PavementManagement System (PMS) beingimplemented by the CED in 1996.

9.6.3 Detailed Survey

Where any significant pavement deteriorationis discovered, a Detailed Survey should becarried out over the affected length andadjacent area. The objectives of this surveyare to obtain a good description of thedeterioration (type, degree and extent) and anindication of the likely causes. The survey willconsist of a more detailed visual survey carriedout on foot, including rut measurements. Nondestructive testing of these pavement lengths,using either Benkelman Beams or a FallingWeight Deflectometer (FWD), may also beuseful at this stage. Deflections can be used tocheck if there is any change in pavementstiffness between a sound and deterioratedsection and should assist in deciding whetherthe deterioration is confined to surface layers oraffects the whole pavement structure. TheFWD will give more detailed structuralinformation as it measures the deflections bowlof the pavement in response to a dynamic load.Using appropriate software, it is possible toback-calculate the stiffnesses of the pavementlayers, provided that the thicknesses of theseare known. In order to produce consistentmeasurements and layer stiffnesses, therecommendations given in the FEHRL (1996)publication should be followed. The stiffness ofasphalt layers are strongly influenced bytemperature and the results of all deflectionmeasurement must be corrected to a standardtemperature. To do this, temperatures in theasphalt layers must be measured at the time oftest.

Where the deterioration is considered seriousor is worsening, strengthening or resurfacingwork will be necessary. However, a DetailedInvestigation will be required to provide furtherinformation to decide precisely what work isnecessary. If the pavement condition is not tooserious, it may be appropriate to merely repeatthe Detailed Survey after, say, one year.

9.6.4 Detailed Investigation

The objective of the Detailed Investigation is toexplain the pavement deterioration, includingthe identification of the layer(s) responsible forthe deterioration and thus provide informationto enable any strengthening to be economicallydesigned. It will normally involve coring andtest-pitting of selected areas of the pavementtogether with in situ and laboratory testing ofthe pavement layers. If deflection testing has

January 1997

SECTION 9

not already been carried out at the DetailedSurvey stage, it should now be carried out.

The investigation must be properly planned andeffort concentrated at locations to produce datawhich will be relevant to explaining thedeterioration. Before planning the investigation,as much background information as possible,applicable to the length of interest, should beassembled:

• Original construction details, includingspecifications

• Local subgrade and drainageconditions

• Maintenance history

• The results of any previous pavementsurveys or investigations

• Past and current traffic flows andcomposition.

Some or all of this information should beavailable from the CED Pavement ManagementSystem. If there are major omissions in thisinformation, then the Detailed Investigation mayneed to be expanded to include tralfic countsand additional cores or test pits. Wherethicknesses are unknown, ground penetratingradar may be of assistance but this techniqueneeds careful calibration against knownthicknesses for each type of pavement beingsurveyed.

The standard investigation strategy is tocompare deteriorated and sound section$ ofpavement (20 to 100m in length) carryingsimilar traffic and of similar construction (theselection of such sections, itself, can sometimesindicate a possible cause of deterioration).Appropriately sited cores and/or test pits shouldreveal any differences in material qualities orthicknesses which may explain the differentperformance. Depending on the variation oftraffic and construction within the length ofinterest, a number of pairs of comparisonsections may be necessary. Where available,deflection and FWD data may be used to selectpairs of sections with high and low deflections.However, adequate explanati·ons for thedifferent stiffnesses are not always found. Themajority of cores or pits should be in thedeteriorated sections, sited right on thedeterioration (cracks, ruts etc) to determineexactly which layers are affected. In the case ofcracking, it is important to know the depth ofcrack propagation and for rutting, whether or notthis is present in both the asphalt andunderlying granular layers. To determine whichlayers are contributing to a rut, or other

Page 9/16


deformation. will require a set of three or morecores. straddling the rut.

SECTION 9

9.6.5 Interpretation and Design ofRemedial Works

The foilowing points should be consideredwhen planning and executing the investigation:

..

..

..

..

..

The cores and test pits arefundamentai to the whole investigationand should ail be carefuily examinedand logged by a competent materialsor pavement engineer. The core logsheets should include a photographwith a scale. fuil details of asphaitthickness and condition. includingtexture. segregation. voids. iayerbonding. width and depth of cracks.stripping. soft or otherwise deleteriousaggregate. bleeding and any otherpeculiarities

Granular layers (sub-base andsubgrade) can be rapidly and cheaplyassessed by in situ testing using eithera hand operated Dynamic ConePenetrometer (DCP) (Kleyn andSavage. 1982)(Jones and Rolt. 1991)or a portable dynamic plate bearingtester (PDPBT) (Roads and TrafficResearch Association. 1992). TheDCP test can be carried out through acore hole but the PDPBT will require atest pit to expose an area of 0.5 by0.5m.

Static plate bearing tests or in situCalifornia Bearing Ratio tests couldalso be carried out in place of the DCPor PDPBT but are slower. more costlyand technically no better than thesehand methods

Decisions on the number and type oflaboratory tests should be made afterthe assessment of the field data.Samples of suspect foundationmaterial should be obtained during theexcavation of the test pits. but notnecessarily tested. Decisions on whatlaboratory tests should be carried outwould be made after the field data hasbeen reviewed

Density testing of sub-base orsubgrade layers wiil be helpful wherethe strength of these layers isunexpectedly low and low compactionis suspected to be the cause. Amaximum dry density value(determined in the laboratory) wiil alsobe necessary to determine relativecompaction.

The interpretation of the data from theinvestigation must address the following issues:

.. What is the nature. extent and degreeof the deterioration?

.. Is only the surfacing or the wholepavement affected?

.. What has caused it?

.. What remedial treatment is needed?

Provided that the Detailed Survey has beenthorough and the Detailed Investigation hasbeen properly planned. the first two issuesshould be answered by a proper presentation ofthe survey/investigation data.

Answers on the causes could be very obvioussuch as an under-designed pavement. poorquality asphalt containing segregated aggregateand voids. or soft and friable sub-base. In othercases the causes may be more subtle requiringdetailed laboratory testing to identify. Inpractice. interpretation should commence withthe completion of the Detailed Survey andcontinue during the planning and execution ofthe Detailed Investigation to ensure thatrelevant and sufficient data is obtained toanswer the main questions. Successfulinterpretation leading to robust conclusionsdepends strongly on having carried out the rightfield work. sampling and testing in the firstplace.

In addition to evaluating the existing pavement.the future design traffic must be estimatedbefore deciding what thickness of overlay will berequired. The methods described in Clause 9.2for new roads are appropriate. Normally.pavement strengthening should be designed fora 20 year life. subject to the comments made inClause 9.2.2.

A possible method of determining overlaythicknesses is to compare the existingpavement thickness with that required to carrythe total of past and future traffic (AASHTO•1993). The overlay will provide the difference inthickness between the existing pavement.Allowance should be made for any difference inquality of existing material and the current QCS.due either to deterioration or a lower originalspecification. Defective or deteriorated wea(ngcourse should be replaced before overlaying.Roadbases with moderate deficiencies could beretained but with a reduced allowance ofthickness.



In cases where reconstruction is proposed, thisshould be designed in accordance with therequirements of the rest of this section.Granular sub-base is not subject to fatigue and,provided that it complies with the currentspecification, is unlikely to require replacement.

9.7 REFERENCES

AMERICAN ASSOCIATION OF STATEHIGHWAY AND TRANSPORTATIONOFFICIALS (1993). AASHTO Guide for designof pavement structures. Washington, DC.

BRITISH PORTS ASSOCIATION (1994). Thestructural design of heavy duty pavements forports and other industries, 2nd edition. London.

CRONEY D and P CRONEY (1991). Thedesign and performance of road pavements,2nd edition. McGraw Hill International,Maidenhead, UK.

DEPARTMENT OF TRANSPORT (1991).Manual of contract documents for highwayworks, Volume 3, Highway construction details,HMSO, London.

DEPARTMENT OF TRANSPORT (1994).Design manual for roads and bridges, Volume7, Pavement design and maintenance, HMSO,London.

FEHRL - FORUM OF EUROPEAN NATIONALHIGHWAY RESEARCH LABORATORIES(1996). Harmonisation of the use of the fallingweight deflectometer on pavements, Part 1.FEHRL Report No. 1996/1. Crowthorne:Transport and Road Research Laboratory.

JONES CR and J ROLT (1991). Operatinginstructions for the TRL dynamic conepenetrometer (2nd edition). TRL OverseasCentre Information Note. Crowthorne:Transport Research Laboratory.

KLEYN, EG and PF SAVAGE (1982). Theapplication of the pavement DCP to determinethe bearing properties and performance of roadpavements. Proceedings of the InternationalSymposium on Bearing Capacity of Roads andAirfields. Trondheim.

MAYHEW, HC and HM HARDING (1987).Thickness design of concrete roads. Researchreport 87. Crowthorne: Transport and RoadResearch Laboratory.

MINISTRY OF COMMUNICATIONS of theKINGDOM of SAUDIA ARABIA (1990).Highway Design Manual. Riyadh.

January 1997

SECTION 9

PORTLAND CEMENT ASSOCIATION (1984).Thickness design for concrete highway andstreet pavements. Skokie, Illinois, USA.

ROAD RESEARCH LABORATORY (1970). Aguide to the structural design of pavements fornew roads. Road Note 29. HMSO, London.

ROADS AND TRAFFIC RESEARCHASSOCIATION (1992). Technical testspecification for soil and rock in road bUilding,Part B 8.3, Dynamic plate-load test using thelight falling-weight device. (In German.)Cologne.

TRANSPORT and ROAD RESEARCHLABORATORY (1990). A users manual for aprogram to analyse dynamic cone penetrometerdata. TRRL Overseas Road Note 8.Crowthorne: Transport and Road ResearchLaboratory.

Page 9/18


ANNEX9A BASIS OF THE DESIGNMETHOD FOR ASPHALTROADBASE

methods are sometimes used to extend theempirical results to wider ranges of traffic orlayer thicknesses, or to slightly differentpavement types.

9A.1 DESIGN METHODS

Analytical and empirical methods can both beused to determine the thicknesses of pavementiayers to carry a specified amount of traffic. Inthe first, the materials to be used in thepavement are characterised by their stiffnessesand fatigue laws, ie. the relationship betweenstrain and the number of load cycies to producefailure. The pavement is then proportioned sothat strains at critical depths, due to standardwheel loads, do not exceed permissible valuesfor the required number of load repetitions (thehorizontal strain at the base of the roadbaseand the vertical strain at the top of thesubgrade are normally considered to be thecritical criteria). The design documentsproduced from analytical methods may consistof either a detailed calculation procedure or aneasily read "catalogue" of diagrams or graphsrelating layer thicknesses to traffic and layerproperties.

The design documents produced from empiricalperformance studies are usually in "catalogue"format with the exception of the AASHTOmethod In which traffic, pavement thickness andmaterial quality are related by an empiricalequation.

In practice, design by either method is oftenchecked to some degree by the other.

9A.2 DESIGN STRATEGY

Conditions in Qatar differ from the temperateenvironments, where both the analytical andempirical methods have been most practised,and need to be reflected in any design for localuse:

• Qatar has a much hotter climate whichwill greatly affect the stiffness of anyasphalt and will affect bitumen ageing

Although the analytical method is technicallyattractive, there are considerable practicaldifficulties:

• Determining stiffness values iscomplicated. Asphalt stiffness varieswith temperature, rate of loading andage of the bitumen. For unboundmaterials, the stiffness varies withmoisture, stress history and confiningstress

9A.3 APPLICABLE METHODS

The material standards in Qatar are similar tomainstream practice elsewhere. '

A significant proportion of heavyvehicles are overloaded causingsignificantly more damage than thesame types of vehicle elsewhere.

Subgrade strengths are generally highdue to the prevalent limestone andsand, and many roads are constructedon low embankments of good fillmaterial

The first stage in determining asphalt roadbasepavement designs for Qatar was to reviewestablished methods or "catalogues" whichcould apply to the hot conditions, either becausethey were empirically derived from theperformance of pavements in a hot climate, orallow the input of low stiffness values. Themethods reviewed are listed in Table 9A.1.

•

•

There is no standardisation of fatiguemeasurement and a wide variety oftests are in use, hardly any of whichare compatible (Tangella et ai, 1990).Consequently, each analytical designmethod has its own load cycles/strainrelationship based on a specific fatiguetest method

The field evidence of fatigue failure, inthe manner assumed in the analyticalmethod, is not conclusive.

•

•

In the empirical method, the performance oftrial pavements is monitored to determine theamount of traffic which can be carried beforethe condition is considered unacceptable.Sometimes the traffic is accelerated bycontinually trafficking by heavy vehicles, as inthe AASHTO Road Trial, or occurs normally, asin the trials carried out in the UK on publicroads. The latter method is the more reliable,however, the trial results are only strictlyapplicable to the trial conditions. Analytical

The methods all quantify cumulative traffic onthe basis of equivalent 80kN (or 8 tonne)standard axles using a 4th power law. The firstthree methods do not require specifictemperature or asphalt stiffness input but thelast three do.



Transverse strain at the bottom of the roadbase

9A.4 SPECIFIC METHOD FOR QATAR

The fatigue laws are:

Vertical strain at the top of the subgrade

The Austroads manual producesdesigns for hot climates which accordreasonably well with performance.

• The manual reflects more recentexperience

•

The second stage in determining asphaltroadbase thicknesses was to set these slightlygreater than the 110 to 270mm values and thenadjust to ensure that the roadbase andsubgrade strains did not exceed permissiblevalues. The fatigue laws from the Austroadsmanual were used for this because:

• Many Australian pavements are built ina fairly hot climate

J1eh = (6532)/(I"P2) for asphalt with a stiffnessof 1.0 GPa, and

Table 9A.1 - Design methods

The Shell method, No.5, gives temperaturedata for Bahrain which is applicable to Qatar.The weighted mean monthly air temperature isgiven as 28°C which results in an effectivepavement temperature of 40°C for a 200mmthickness of asphalt. Two methods ofdetermining asphalt stiffnesses at this higheffective pavement temperature have beenconsidered:

No Temp. APpli~~~e Design MethodInout Count

1 No Tropical and A Guide 10 the StructuralSub-Tropical Design of Bitumen-Surfaced

Countries Roads in Tropical and Sub-Tropical Countries (TAUOD~':l\Overseas Road Nole 31, 1993

2 No South Alrica Structural Design of Interurbanand ~~~al Aoad ~:ivements.TRH4 CSJR, 1985

3 No Saudia Arabia Highway Design Manual

4 V" USA AASHTO Guide for Design ofPavement Struclure;11993\

5 V" International ~he!~iavement Design Manual1978

6 Va, Australia ~avemenl DeSiT,n\Austroads. 1992

• The standard stiffness nomographs(Van der Poel, 1954 and Bonnaure etai, 1977) indicate stiffnesses between 1and 3 GPa for MD1 asphalt roadbase

Jlf:,= (8511)/([lf14)

( Jlf: = microstrain and N =number of loadrepetitions. )

An asphalt roadbase stiffness of 1.0 GPa hasbeen used in the AASHTO and Austroadsmethods. The South African, AASHTO andTRL Overseas methods all indicated verysimilar thicknesses of 110 to 270mm of asphaltfor 1 to 50 million standard axles. All the others,in varying degrees, were thicker.

These are appreciably higher than the values ofonly 0.3 to 0.6 GPa indicated in the Shellmethod, which are considered to be too low.Partly as a consequence of these lowstiffnesses, the Shell method indicates muchgreater pavement thicknesses compared to allthe other methods except for Saudia Arabia.The satisfactory performance of roads in hotenvironments with much thinner asphaltroadbases than the Shell designs suggests thatthe method is conservative for these conditions.

• Back calculation of falling weightdeflectometer data from Qatar indicatesan average roadbase stiffness of over 3GPa for mature asphalt. Similaranalysis of data from 18 month oldMalaysian pavements indicates asphaltroadbase stiffness of 1.5 to 3.5 GPa at40°C.

The layer stiffnesses and Poisson's ratios usedto determine the strains are shown in Table9A.2.

Description CBR% Stiffness Poisson's(GPa) Ratio

Asphalt 1.0 0.35Stiffness

Granular 60 0.200 0.35Sub-base

Subgrade 50 0.170 0.45

Subgrade 25 0.125 0.45

Subgrade 15 0.100 0.45

Subgrade 10 0.075 0.45

Table 9A.2

(5% voids, 4% of 60170 Pen bitumen at atemperature of 40°C)

(1 GPa = 1 Gigapascal = 1x10' N/rrf and 1 MPa= 1 Megapascal = 1x10' N/ni)

The standard approximate relationship forsubgrade stiffness, E (MPa) = 10 x CBR (%),only applies to low strength material. The above



values are based on those determined eitherfrom plate bearing tests or back analysis offalling weight defiectometer data.

In ali cases, asphalt fatigue was found to 'be thecritical criterion.

9A.5 WEAK SUBGRADES

In Clause 9.3.2, the minimum subgrade strengthincluded in the design charts was set at a CBRof 15% at in situ density which is generallyachievable. However, in the smali number ofcases where the in situ subgrade strength fallsbelow this, it will be necessary to provide a layerof stronger material calied "capping" betweenthe subgrade and the sub-base. The cappingwili normally be either the 15% or 25% CBRsubgrade material used in the standard designsand wili have the same stiffnesses as above. Incuts or where the road surface is close toground level, some of the subgrade will have tobe removed and replaced with capping. In filisituations, the upper earthworks layers must beconstructed with the capping material. Amethod of determining the necessary cappingthickness for either case may be based on thesurface stiffness at formation level, ieimmediately below the sub-base.

The minimum strength standard subgrade(Class S1) consists of at least 0.3m thickness ofCBR 15% material (or stronger) resting onmaterial with a CBR of at least 10%. A 40kNsingle wheel load at formation level wili producea surface deflection of 1A9mm. The thicknessof the capping layer required for a weakersubgrade will be that which produces the samedeflection for the same load. The thickness willbe determined by trial and error using an elasticlayer programme to model the stiffnesses of thesubgrade layers. For the cases of subgradeCBR values of 7%, 5%, and 3%, the requiredthicknesses of CBR 15% capping wili be 0.5,0.9 and 1.9m. For the weaker subgrades ofCBR 5% and 3% it wili be more effective to usethe stronger CBR 25% capping in thicknessesof 0.35 and 0.7m respectively. Other cappingthicknesses are possible depending on specificstrengths or stiffnesses, but for practicalreasons the thickness should not be less than0.2m.

The stiffnesses and Poisson's ratio used in thisanalysis are shown in Table 9A.3.

Descriplion CBR% Stiffness Poisson's(MPa) Ratio

Capping 25 125 0.45

Capping 15 100 0.45

Subgrade 'A 75 0.45

Subgrade 7 65 0.45

Subgrade 5 50 0.45

Subgrade 3 30 0.45

Table 9A.3

January 1997

SECTION 9

Capping material of greater strength may beused. However, in determining the thickness,higher stiffness values should be used withgreat caution as the in situ stiffness isdependent not just on the quality of the cappingbut also on the stiffness of the underlyingmaterial.

9A.6 REFERENCES

AMERICAN ASSOCIATION OF STATEHIGHWAY AND TRANSPORTATIONOFFICIALS (1993). AASHTO Guide for designof pavement structures. Washington, DC.

AUSTROADS (1992). Pavement design - aguide to the structural design of roadpavements. Sydney, Australia.

BONNAURE F, G GEST, G GRAVOIS and PUGE (1977). A new method of predicting thestiffness of asphalt paving mixtures.Proceedings of the Association of AsphaltPaving Technologists, Vol. 46.

COUNCIL FOR SCIENTIFIC AND INDUSTRIALRESEARCH (CSIR) (1985). Structural design ofinterurban and rural road pavements. Technicalrecommendations for highways (TRH 4).Pretoria, South Africa.

SHELL INTERNATIONAL PETROLEUM CO.(1978). Sheli Pavement Design Manual,London.

TANGELLA SCSR, J CRAUS, JA DEACON andCL MONISMITH (1990). Summary report onfatigue response of asphalt mixtures. StrategicHighway Research Program, Report f>HRPA/IR-90-011. National Research Council,Washington, DC, USA.

TRANSPORT and ROAD RESEARCHLABORATORY (1993). A guide to the structuraldesign of bitumen-surfaced roads in tropical andsub-tropical countries. Overseas Road Note 31,fourth edition. Crowthorne: Transport and RoadResearch Laboratory.

VAN DER POEL C (1954). A general systemdescribing the visco-elastic properties ofbitumen and its relation to routine test data.Journal of Applied Chemistry; VolA.

Page 9/21

QATAR HIGHWAY DESIGN MANUAL SECllON10

SECTION 10 ROADWAY LIGHTING

10.1 INTRODUCTION

10.1.1 Reasons for Lighting

Highway lighting is provided to aid the safe andorderly movement after dark of all road users,both vehicular and pedestrian.

For the driver, properly designed lighting willincrease his range of vision, reveal hazardsmore effectively, reduce fatigue and particularlyin the case of high-speed roads, increase thetraffic carrying capacity. Pedestrians will beable to orientate themselves and to detectvehicular and other hazards. From the policepoint of view, crime directed against the personand property will be discouraged, whilstsurveillance and recognition will be greatlyenhanced, particularly if good colour renderingis provided.

measured in terms of reduction inpersonal injuries, fatalities, propertydamage, and other costs to society.More effective usage of the road andthe possible increase in its capacity arealso considered.

10.1.3 Scope

This section of the Manual sets out theperformance requirements and standards whichshall be adopted for the design of lighting on alltypes of highway in Qatar, except for thosefootpaths which are separated from vehicularroutes.

10.1.4 Complementary Standards

This section of the Manual requires the use ofBS 5489 : Road Lighting: Parts 1-10 : 1992.

10.2 PERFORMJl.NCE REQUIREMENTS

10.1.2 Justification

In considering whether a road should be lit,from an engineering point of view, the followingfactors should be considered.

.. The nature of the road (eg. motorwayor mixed traffic road) as determined byits geometry and also by its night trafficaccident rate.

.. The traffic intensity and composition(eg. fast traffic only or mixed traffic).

10.2.1 Summary of Road Classifications inQatar

Individual roads in the State of Qatar each fulfillcertain functions within the overall network. Ahierarchy exists which defines their variousroles and the position of a road within thishierarchy is a measure of its nationalimportance. Route classification is discussed atthe front of this manual. Table 10.1 shows therelationship between the classification used inthis manual and the classification used byMinistry of Electricity and Water, Street LightingSection.

.. The danger points and other specialsituation, such as junctions, crossingsfor cyclists and pedestrians and otherinterruptions in driving continuity whichmay present drivers with unexpectedsituations.

.. It is particularly important to avoidsudden changes in the visual field ofthe drivers as far as determined by thelighting and to allow drivers to preparethemselves well in advance formanoeuvres which suit the situation tobe met over the next stretch of road.

Refer to Table 1.1 for full descnptlons of the HighwayClassification.

Category Description Highway Class(Refer Talile 1)

Class 'A' MOIO/ways or Express P1, P2Roads (eg Doha-RuwaisRoad, Doha - Abu SamraRoad)

Class 'B' Ring and Radial Roads P1. P2, S2

Class 'C' Commercial and Shopping S2, TR1. TR2Sireets

Class '01' Distributor Roads TR1. TR2

Class '02' Local Sireets, Residential TR3, TR4, TR5Roads or Access Roads

Road Classifications in Qatarfor Roadway Lighting

Table 10.1

Factors such as traffic volume, speed,road use during the night, nightaccident rate, road geometry, andgeneral night visibility conditions areimportant when considering highwaylighting.

..

.. Justification for lighting is also basedon the economics of lighting ascompared to the cost of not lighting.Economic returns for lighting are



10.2.2 Lighting PerformanceRecommendations

Minimum designed performance levels for thevarious classes of road are given In Table 10.2.

Category Maintained Overall Longitudinal Me<Average Unlformity Uniformity Threshold

(Class) luminance Ratio Uo Ralio Ul IncrementLAV cd/m~ TI%

'A' 2.5 0.4 0.7 10

'B' 2.0 0.4 0.7 10

'C' 2.0 0.4 0.7 20

'01' 1.25 0.4 0.5 20

'D2' 0.75 0.4 0.5 30

SECllON10

Light PollutionAnother effect of lighting is 'sky glow' whichoccurs when upward stray light is reflected backto earth. Although some sky glow from majorconurbations is unavoidable, special careshould be taken when designing road lighting inareas where little exterior lighting exists, to limitthe amount of upward or stray light. Such areasshould be considered to be environmentallysensitive at night and special light controllanterns specified. As well as hinderingastronomers, many people feel that this form oflight pollution diminishes the aestheticproperties and value of the dark night scene.

10.3 RECOMMENDED PRACTICE

10.3.1 Decisions Prior to Design

For slip roads and shoulders on Class 'A' andClass 'B' roads, maintained average luminancevalues of 2.0 and 1.25 respectively will beacceptable, but the other parameters shouldremain unaltered.

Table 10.2 Lighting Requirements forTraffic Routes

Arrangement and Mounting HeightLantern arrangement and mounting height shallbe in accordance with the options set out in BS5489 : Part 2 within the local geometric,maintenance and environmental constraints thatapply. Greater mounting heights shall beconsidered, particularly for wider carriageways.

10.2.3 Limitation of Glare and "LightPollution"

Disability GlareDisability glare, defined and discussed in BS5489 : Part 1, reduces the contrast betweenobjects and their background, so that theirvisibility is decreased. An object that is justvisible (that is at the threshold of visibility) whenthere is no disability glare will, in the presence ofdisability glare, merge into the background. Thepercentage by which the background luminancehas to be increased to render the object justvisible again is known as the thresholdincrement (Tl). This provides a notionalmeasure of disability glare from installations.

The value of the Tl depends on the light.distribution from the luminaire between 70' and900 in elevation in the vertical plane at which theluminaire is observed, usually within 10' ofazimuth of the transverse axis of the luminaire.It also depends on the road luminance, thelayout of the luminaires, the mounting height andthe observer position.

Discomfort GlareControl of the Tl within the limits recommendedin Table 10.2 will generally ensure thatdiscomfort glare, defined in BS 5489 : Part 1, willbe adequately controlled.

January 1997

Limitation of GlareThe performance requirements of Clause 10.2shall be met by the selection of lanterns asdescribed in BS 5489 : Part 2.

In order to limit the glare factor on roads Class'A' or 'B' where the surrounds are dark, lanternsmust be flat glass type with a distinct cut-offlimiting the visual aspect of the light source toan angle of 30' from the horizontal. Lanternswill be mounted at a minimum height of 12metres from the road surface.

For Class 'C' roads where the surrounds aremostly bright, the mounting height will be aminimum 10 metres and either cut-off lanternsor lanterns having a prismatic controller will bepermitted.

Class '0' roads where the decorative andaesthetic aspect dominates (e.g. Pole toplanterns) should use diffusers to eliminate bothdiscomfort and disability glare. The mountingheight for such lanterns shall be from 3 to 8m.

OverhangOverhang shall be in accordance with theoptions set out in BS 5489 : Part 2. Bracketprojection generally shall be as small aspossible in order to minimise vibration effectson both the lamp and the column itself.

For aesthetic reasons, the bracket arm isusually limited to one quarter of the columnheight (ie. H/4), as longer arms can give theimpression that the column is top heavy.

Page 10/2


The Light SourceIn order to conserve energy and achieve highefficiency, Qatar has standardised on highpressure sodium lamps for Class 'A' and 'B'roads and high or iow pressure sodium lamps forClass 'C' roads. Class 'D' roads may be lit withsodium, high pressure mercury, metal halide orlinear compact fluorescent.

Maintenance FactorMaintenance factors, as defined in BS 5489 :Part 2, shall be taken for designs from Table 4 ofthat Standard.

The necessity for lantern cleaning at morefrequent intervals than lamp changing will beavoided if a minimum degree of ingressprotection rating of IP65 is specified.

Road SurfaceDesign tables based on the 'representativeBritish road surface' as given in Table 3 of BS5489 : Part 2 may be used.

However a more economical lighting design ispossible if a concrete road surface is to beprovided. If at a later stage the concrete surfacemay be overlaid with bituminous material thenthe lighting shall be designed for this initially.

Where design calculations are carried out bycomputer, a range of characteristic road surfacereflection tables may be input from PublicationCIE No. 30-2 : Calculation and Measurement ofLuminance and Illuminance in Road Lighting.Most proprietary lighting calculation programswill contain data files for one or more of thesestandard road surfaces.

10.3.2 Standard Lighting Geometries for. Different Road Profiles

Road authorities are primarily concerned withroad lighting for its accident reducing potential.However, these benefits can be seriouslydiminished if insufficient attention is given toreducing the hazard created by lighting polesnear the roadway.

Whilst the development and application ofgeometric standards for roads and streets hasreduced the variation in roadway layout forvarious classes of roads, the road lightingdesigner is nevertheiess confronted with a largenumber of road layout features and conditionswhich will influence the lighting design.

Divided or Dual Carriageway RoadsThis type of roadway layout is most common forhigh volume urban and rural arterial roads.Such roads may involve cross sections withservice roads on one or both sides of the maincarriageways, a great range of median and outerseparator widths and often with carriageways

January 1997

SECTION 10

(inciuding service roads) constructed atdifferent levels.

The presence and location of existing roadfurniture and service utilities such as powerdistribution lines, telecommunications, andvarious underground services may imposecertain constraints on the lighting layout.

The location and form of major intersections,median openings and other traffic facilities suchas pedestrian crossings and bus stops mustalso be considered.

Thus the road lighting designer must becompletely familiar with the section of road tobe lit and equally important, he should have agood understanding of traffic operations thatoccur particularly during night time. It is onlywith this knowledge that he can arrange thelighting layout to best meet the many controlsand demands of individual sites and achievethe maximum lighting effectiveness atreasonable cost.

The general lighting arrangement will of coursebe dependant on the roadway width, luminairesavailable and the desired mounting height inaccordance with the design rules andprocedures as set out in BS 5489 : Parts 2 and10. However, a choice of several layouts willusually be available to the designer.

On dual carriageway roads any of the followingarrangements of luminaires may beappropriate:

a) Single Sided Arrangement.

Single sided arrangement on each carriagewaywith luminaires mounted on the right hand side.In some cases the mounting height possibleeven with special brackets will be inadequatefor the width of carriageway and an alternativearrangement will be required.

b) Opposite Arrangement.

On dual carriageway roads, an oppositearrangement involving poles mounted along theright (footpath) side of each carriageway maybe appropriate where the carriageways are nottoo wide and the median is narrow.

c) Twin Central.

This arrangement provides the designer withthe greatest flexibility in locating luminaires butrequires the minimum median width to be atleast 1.8m and preferably wider. The choice ofmounting height is flexible, as clearances tooverhead distribution lines will generally not bea problem.

Page 10/3


This layout can be considered the most suitabiefor dual carriageway arterial roads, particulariythose with carriageway widths greater than 10m,because of the following advantages:

.. The number of poles can be minimisedby selecting the highest practicalmounting height.

.. The installation cost is often lower thanother layouts because of lessunderground cabling and oniy one rowof poles.

.. This layout provides excellent routeguidance.

.. It is often feasible to install guard fencesat hazardous locations where vehiclecollisions with poles become a problem.

Undivided RoadsUndivided roads form the major length of urbantraffic routes. They are usually bordered byrelatively narrow verges and footpaths whichmay contain overhead power distribution lines.

On these roads the designer is often confrontedwith constraints such as clearance of powerdistribution lines, location of undergroundservices, location of driveways and commercialentrances and often the presence of trees etc.which will make an optimum layout difficult toachieve.

In general, single sided arrangements will rarelybe practical and depending on the width to be litand mounting height available, a staggered oropposite arrangement must be selected.

On wide undivided roads (and sometimes ondual carriageway roads) there is a tendency bylighting designers to locate the luminaires wellout over the carriageway, in an attempt toachieve a single sided arrangement. Suchlayouts are generally unsatisfactory because of

.the 'flash' produced as vehicles pass directlyunder the luminaires and more importantly, theverge and footpath area is often poorly lit as aresult of the overhang exceeding H/4, refer toClause 10.3.1 Overhang.

CurvesBS 5489 : Part 2 sets out the requirements forspacing luminaires around curves. This usuallycalls for the luminaires to be located on theoutside edge of the curve which is in conflict withnormal road safety requirements to avoidlocating obstructions at such locations.

It is suggested that unless the curve is quitesharp (which would be unusual on a traffic routeof reasonable standard) the designer should

January 1997

SECTION 10

forgo the use of the sighting gauge and simplyclose up the spacing slightly to raise thegeneral ambient light level to compensate.

It should be remembered that true silhouettevision against the road pavement asbackground will generally not be achieved oncurves and drivers will be seeing by eitherdirect vision or by silhouette vision againstfences, buildings and trees, etc. along theverges.

CrestsThe designer will generally follow normal 'evengrade' procedures when crests are encounteredon the section of road to be lit. However, if thecrest is relatively sharp, as might exist wherethe road overpasses another road,consideration should be given to the use of cutoff rather than semi-cut-off luminaires. Oftenthis should involve only one or two luminaires atthe top of the crest.

10.3.3 Lighting Columns as Hazards

Road accidents involving fixed objects besidethe roadway are a considerable concern toeveryone involved with roads and traffic.

Table 1 of BS 5489 : Part 1 recommendsminimum clearances between columns andedge of carriageway for a range of designspeeds.

10.3.4 Typical Lighting Layouts atJunctions

Junctions are particularly important elements ofthe road system both from the point of view ofefficient traffiC operation and of road safety.The latter is evidenced by the fact that at least60% of casualty accidents in urban areas occurat these locations.

It is especially important, therefore, that thelighting standard at junctions be at least asgood and preferabiy somewhat better than thaton the intersecting roads. In addition, theimportance of minimising the number of polesand/or locating them clear of vulnerable areascannot be overstressed.

BS 5489 Part 3 makes specificrecommendations in respect to the positioningof key luminaires at simple intersections andthe engineer should conform with theserequirements as far as practical.

The large variety of channelization layouts,each designed to meet the specific site andtraffic conditions at any particular location,makes it difficult to set down standard luminairearrangements. However, some rules relating to

Page 10/4

QATAR HIGHWAY DESIGN MANUAL SEC110N10

luminaire arrangement can be formulated toguide the lighting designer in the achievement ofgood design practice:

.. The luminaire layout as seen inperspective should not confuse butenhance the route of through traffic. Agood layout will provide route guidanceto lead traffic through the junction

.. At the outset, the engineer mustrecognise that seeing by silhouettevision is unlikely to occur at junctionsand as a result, the layout should aim atilluminating the conflict area and theobjects in and around it, such aspedestrians, cars, kerbed islands,pavement markings and signs etc. sothat they are seen by direct vision

A

Typical Layout for T-Junction

i Appr.I 1/3S

I1/2sI ,

I

I I D I-~III Appr.II 1/25

B A : c"-

Note: S = design column spacing on the main road.

•

.. At roundabouts in the small approachsplitter islands, on the central islandopposite entry roadways and on theright hand side immediatelydownstream of an entry point to aroundabout.

Figures 10.1 to 10.6 show typical lightinglayouts recommended for standard junctiondesigns in Qatar.

Figure 10.1

Luminaires must be placed to providethe best possible illumination ofpedestrian crossing areas

The level of illumination and itsuniformity should be such that the layoutof the islands and the variouscarriageways and turning roadways areclearly discernable by driversapproaching on the intersecting roadsand negotiating the required movementswithin the junction

..

..

.. Care should be taken to ensure thatpoints where traffic streams merge anddiverge are well lit

.. The number of lighting poles near theconflict area should be minimised.Where traffic signals are installed orbeing installed, joint sharing of thepedestals should be achieved whereverpossible. Where large channelizingislands exist, consideration should begiven to the use of high mast floodlighting techniques to reduce thenumber of poles around the junction.

It is very important to avoid locating poles:

.. Close to the approach ends of narrowresidual medians and median islands

.. In the nose area of islands where trafficstreams diverge

.. In areas where the poles might obstructthe sight lines of drivers waiting to enteror cross another traffic stream

.. In the vulnerable areas along theoutside of curved slip roads



10.5.6 Safety Standards

Engineer's ResponsibilitiesIn order to promote safe working practices forboth construction and maintenance, the designengineer shall carry out Risk Assessments forany activities which may endanger personnel orproperty, including the following where relevant:

Working at height

Use of mobile elevating workingplatforms

Storage and use of liquid propane gas

Storage and use of highly flammableliquids

Slinging of loads

Use of lifting equipment

Use of hand tools

Use of compressors and pneumaticpower tools

Use of portable electrical equipment

Electrical work up to 415 volts

Installing/replacing luminaires

Electrical testing and commissioning

Disposal of discharge and fluorescentlamps

Disposal of waste materials

Work in the vicinity of undergroundservices

Work in the vicinity of overhead electriccables

Work in and with excavations

Roadworks

Minor demolition and breaking out ofservices.

10.6 MAINTENANCE AND OPERATION

10.6.1 Design Implications

It is often important to consider the implicationsof the lighting maintenance operation during theplanning and design of a road lightinginstallation. This is particularly so in respect tolighting on motorways and other high trafficvolume and/or high speed roadways.

January 1997

SECl10N10

Most road lighting maintenance is carried outusing elevating platform vehicles (EPV). Theseare available in various sizes to service up toabout 21 m mounting height, but are expensiveto purchase or hire.

On most lighting installations, the maintenancevehicle will stand on the carriageway directlyunderneath the luminaire, thus reducing thetrafficable width available during maintenanceoperations.

Where the mounting height is 12.5rn or less andthe EPV can be positioned directly beneath theluminaire, outrigging stabilizers may not berequired. In other situations, the use ofstabilizers will be necessary and will furtherconsiderably reduce the trafficked widthavailable.

Depending on the nature of the road in questionand the traffic demands, it will be necessary toimplement appropriate traffic control measuresand possibly even schedule the maintenancework to periods of low traffic flow.

These arrangements can be both inconvenientand costly and the alternatives available shouldbe properly evaluated. The alternatives mayinvolve a different luminaire arrangement at alower mounting height, the use of hinged poles(which are now available at relatively littleadditional cost) or the use of a fewer number ofgreater mounting height columns with luminairelowering gear (high masts).

10.6.2 Quality of Equipment

When comparing costs of alternative items ofequipment, the "whole life" cost ,of theinstallation should be considered rather thanjust the initial construction cost. It will often befound that more expensive, high qualityequipment requiring less maintenance attentionwill be cheaper in the long run, as well ascausing less inconvenience to the road user interms of obstruction to the highway duringmaintenance operations. There may also besafety benefits in using high quality equipment.

Guidance on luminaire maintenance factors isgiven in Table 4 of BS 5489 : Part 2.

10.6.3 Inventory and Fault Reports

In order to obtain the most cost effective servicefrom a lighting installation, adequate proceduresfor the reporting and logging of faults, and theplanning of maintenance programmes need tobe established.

An essential requirement for these activities isthe provision of an accurate, comprehensive,easily accessible inventory system, nowadays

Page 10/8


usually installed on a desk-top computer or PCnetwork. A large amount of manual survey andlogging work is involved initially, but this will berepaid within a fairiy short time byimprovements in efficiency of management.

It is of great benefit when logging fault reports,which may often originate from persons with notechnical knowledge, to be able instantly to viewdetails of the installation on a visual displayscreen.

10.6.4 Cleaning and Lamp Replacement

It is essential that cleaning and lampreplacement routines should be closely followedto maintain the installation. Maintenanceprogrammes should include lamp replacement,luminaire cleaning, renewal of failed parts,checking of gaskets and optical components,lubrication, painting and night inspections.

Apart from the deterioration of luminaire parts,which can be corrected by cleaning, there isalso a longer term deterioration which ispermanent and cumulative. Restoration ofphotometric performance may, therefore,require replacement of optical systems or eventhe whole luminaire. Site tests should becarried out at intervals of not more than fiveyears to check that performance is acceptable.

The procedure according to which lamps arereplaced is a matter of local policy, cost andlamp type used. The cost of replacing lampson demand should be compared with that ofgroup replacement. In making the comparison,the following factors are among those thatshould be considered:

The shape of the lamp survival curvefor its environment

The lamp lumen depreciation curve

Ease of access, e.g. extent of signingand coning required

Interference with traffic

The required frequency of patrolling foroutages

The frequency of need for cleaning ofluminaires

The overall proportion of outages thatcan be tolerated

The grouping of outages that can betolerated

January 1997

SECTION 10

The frequency of inspection forelectrical safety.

It will normally be found that lantern cleaning,which is a costly, labour-intensive activity, canbe restricted to coincide with the lamp-changingoperation if a luminaire with enclosureprotection to at least IP65 is installed.

10.6.5 Frequency of Inspections

It is recommended that visual, structural andmechanical inspections of street lightingequipment should be undertaken annually withfull electrical testing every five years.

10.6.6 Hours of Operation

Road lighting is required during all the hours ofdarkness, independently of traffic flow, andshould normally be in full operation from about30 min after sunset to about 30 min beforesunrise.

Questions of local policy are outside the scopeof this guide, which deals only with technicalmatters. However, it should be noted thatlighting serves emergency services, publicsecurity and pedestrians as well as drivers andthat extinguishing lighting during the hours ofdarkness is detrimental to these interests.

The practice of extinguishing certain luminaireswhen the traffic flow is small does not fulfil thelighting needs of vehicular traffic and mayincrease the likelihood of collision with columns.

Page 10/9


APPENDIX A SURVEYS A2 SURVEY IN QATAR

APPENDIX A

A1 INTRODUCTION

Survey is a specific discipline, the results ofwhich are utilised for a great many purposesfrom planning to construction.

With regard to road design, the purpose ofsurvey is twofold.

Firstly, it is required to establish the roadway linewithin the context of existing land ownership orplanning requirements, thus fixing the availablecorridors for the roadway and associatedutilities.

Secondly, it is required to identify elementswhich exist within and adjacent to a corridor inorder that a satisfactory road design can beaffected.

To complete this function it is important that thesurvey contractor provides all the informationthe engineer needs and that the engineer makesfull use of all the survey information available.

Survey work in Qatar is controlled by its owncomprehensive specifications and regulations.As such, this appendix is not intended as asurvey manual but as an aid to the highwayengineer, to enable the production ofcomprehensive designs whilst having dueregard for existing and proposed site features.

Items specifically covered are:

• Government bodies controlling surveywithin Qatar

• Survey information useful to thehighway engineer that is currentlyavailable from each organization

• Survey information that should becollected for use on road designprojects

• Procedures required by the CivilEngineering Department for surveywork associated with road designprojects.

Survey during road construction is not coveredwithin this appendix. However, the generalrequirements of as-built surveys are discussed.

January 1997

Survey in Qatar is controlled by the Ministry ofMunicipal Affairs & Agriculture (MMM) and theCentre for Geographic Information Systems(CGIS) who obtain, update and keep thecurrent survey data, and set the criteria bywhich survey data is recorded and presented.

The Qatar Survey Manual, issued in 1989 bythe Ministry of Industry & Public Works,(subsequently replaced by the Ministry ofMunicipal Affairs and AgricUlture) andamending circulars, deal principally withcadastral, control, engineering andhydrographic survey. This includes thespecifications, accuracy and workingprocedures to be used when undertaking thesetypes of survey relating to the Qatar NationalGrid (horizontal position) and Qatar NationalHeight Datum (level).

In addition to survey controlled by the MMAA,the Centre for GIS produces and maintains theGeographic Information System(GIS) for Qatar.

For convenience, this appendix lists the varioussurvey bodies that offer services and functionsuseful to the highway engineer. Theorganizations are illustrated in Figure A1. Eachorganization operates its own specificprocedures and methods that should beadhered to if interfacing with it.

Page A/1

QATAR HIGHWAY DESIGN MANUAL APPENDIX A

CentreforGIS

Q_._---_..

1

P!anning !• Department i

i_~~ "~J

Mapping &Positioning - - - - - - -

Section

LandInformation

Centre

General

SurveySection

_,__1__--,

! I-lighway

~ Design,I Section1_. ,---------'

CEOSurvey

Unit

Figure A1 MMAAlCGIS - Survey Related Organizations

January 1997 Page AJ2


A2.1 Centre for GIS - Mapping andPositioning Services

The Centre of GIS was established in 1990 withthe target of setting up, operating andmaintaining a Geographic Information Systemfor Qatar.

National Control and BenchmarksThe 1" - 41h order survey control points andbenchmarks situated around Qatar provide coordinate and level information for the entirecountry. A greater density of control is given inthe urban areas.

The Geographic Information System is an easilyaccessible digital library of all surface andsubsurface features in Qatar. It is therefore animportant tool for planning and co-ordinating alldevelopments in Qatar.

Because of the link GIS naturally forms with allbodies associated with development, eachgovernment discipline that encompassesconstruction of new features includes a GIS coordinator. In addition, the Centre for GISemploys survey teams who check and collectnew features for inclusion within the digitaldatabase.

OrthoimageryOrthoimagery comprises digital aerialphotography that is assembled to form a visualpicture of the landscape. It has an accuracy of±500mm with a greater resolution in urbanareas. The digital orthoimagery database is notgenerally made available due to the amount ofinformation contained within the files (typically60MB/sheet).

• 1:1000 orthoimagery is available forurban areas of Doha, Wakrah andDukhan. This is useful for engineeringstudies and as a check on field data

Functions of the Centre for GIS useful to thehighway engineer are listed below.

The larger scale digital mapping was created bydigitizing existing maps.

The DBMD is constantly updated sheet by sheetfrom aerial and ground observations.

Topographical DatabaseThe digital topographical mapping database isavailable at nominal scales of 1:500,000,1:200,000, 1:50,000, 1:10,000 and 1:1000(urban areas only).

The 1:10,000 and 1:1000 high resolutiondatabases are stereo-compiled from aerialphotography and form Qatar's GIS Digital BaseMap Database (DBMD).

Aerial PhotographyThe earliest black and white photography takenin 1947 is still available. Completephotographic cover of Qatar dates from 1977and colour photography is generally availabledating from 1980.

• 1:10,000 orthoimagery is available forthe whole of Qatar. This is useful forengineering studies, particularlyrelating to the identification of drainagecatchments and wadi locations.

Digital Elevation ModelThe digital elevation model consists ofaccurately recorded spot heights for the wholeof Qatar.

Aerial photography for the whole of Qatar ispresented at scales of approximately 1:40,000and is useful for route and developmentplanning and engineering studies. Wadiconditions, areas of high water table andflooding are clearly identifiable from the aerialphotography.

Satellite ImageryAvailable in digital format and posters for thewhole of Qatar. Satellite imagery is notgenerally used in highway design but is usefulfor specific studies because additionalinformation that is not available on the digitalmapping or orthoimagery is presented.

Levels are related to the Qatar National HeightDatum and quoted to two decimal places.

1:50,000 mapping has an accuracy of±25m and is suitable for presentationstyle diagrams.

1:10,000 mapping has an accuracy of±3m which is suitable for location plansand diagrams.

1:1000 mapping has an accuracy of±500mm which is acceptable for moststudies and concept road design and isuseful as a back-drop for illustration ofareas adjacent to the route underconsideration

•

•

•

January 1997 Page A/3


Old MappingEarly map series are available on film or papersheets from archives. The mapping wasproduced from aerial photography taken during1971,1973,1977,1980 and 1987. Scales of1:200,000, 1:100,000, 1:50,000, 1:20,000,1:10,000, 1:5,000, 1:2000, 1:1000 and 1:500have been prepared, though not all areas ofQatar are covered by each scale. The engineershould refer to the Qatar Survey Manual forfurther details of coverage and series.

Old mapping is useful for identifying featuressuch as sink holes, shore lines and low areassince covered by development.

Global Positioning System (GPS)The global positioning system provides positionand level of any place in the world from satellitegenerated location information. A minimum of3 satellites need to be operational over thelocality. GPS equipment may be small enoughto be hand-held. Varying levels of horizontaland vertical accuracy are available, dependingon the number of satellites read and theoccupation time at the station.

The Centre for GIS broadcasts VHF correctioninformation for use with GPS equipment withinQatar to provide real time outputs.

GPS has much use in route finding and striplevel surveys in areas where more accuratecontrol is not available. However, in Qatarwhere accurate control is widespread across thewhole country, its uses are limited by the costrequired to achieve the accuracy necessary forhighway design.

A2.2 Land Information Centre - GeneralSurvey Section (GSS)

The Land Information Centre was created in1994 and incorporates the General SurveySection.

Functions of the General Survey Section usefulto the highway engineer are listed below.

Cadastral DatabaseThe GSS maintains a database of registered coordinates relating to land ownership boundariesfor the whole of Qatar. The information isavailable in the form of co-ordinated points intext files.

Cadastral information shall be used by the roaddesigner for the production of road corridor andnetwork plans and in the computation of roadintersection points and centrelines.

January 1997

APPENDIX A

Approval of Survey CompaniesThe GSS is responsible for the approval ofprivate survey companies who can accesscadastral information and undertake cadastralsurvey work for private or government bodies.

Approval of Corridor Intersection PointsFor new corridor alignments the calculation ofcorridor intersection points and curveparameters shall be made by the highwayengineer or surveyor based on adjacentcadastral information.

Where there is no existing adjacent cadastralinformation, corridor IP's and curve parametersshall be computed from Planning Departmentpolicy plans. Existing site features such aswalls, pylons, posts etc may be used to defineboundaries reflected on the policy plans. Thecomputed corridor IP's and curve parametersshall, in this instance, be reported for theapproval of the General Survey Section.Companies that are approved for cadastralsurvey work by the General Survey Sectionshall be employed to compute and report thesepoints.

Highway engineers are reminded that roadalignments shall be developed in accordancewith the relevant sections of the QHDM.Alignments are therefore not defined by thecorridor centreline (Refer to Section 5).

A2.3 Planning Department

The Planning Department is responsible for theco-ordination of all land planning in Qatarincluding the outline approval of privatedevelopments.

Functions of the planning department useful tothe highway engineer are listed below.

Policy PlansThe Planning Department can provide currentpolicy plans illustrating information regardingland use allocation for the whole of Qatar.

Policy plans are available at scales of 1:1000for urban areas and 1:2000 for rural areas.

Paper copies of policy plans are availableillustrating the up-to-date land use planning.Digital copies of the policy plans are updatedevery three months, and are also madeavailable for general use.

Page A/4


A2.4 CEO Survey Unit

The CED Survey Unit operates exclusively forthe Roads Division. Its main activities are listedbelow:

• Topographical surveys for in-housedesign work

• Setting out for grading schemesundertaken by the Direct LabourOrganisation.

Functions of the CED Survey Unit useful to thehighway engineer are listed below.

Road Intersection PointsThe CED Survey Unit maintains a database ofroad intersection points.

IP's computed by the highway engineer fromcadastral information shall be submitted to theCED Survey Unit for review.

APPENDIX A

A3.2 Services Surveys

Services survey shall be undertaken utilisingelectronic radio-detection methods. Line andlevel of existing services apparatus shall berecorded on services survey plans.

Services survey drawings shall be prepared at1:500 scale for urban areas on A1 sheets andin digital format. Scales for use in rural areasshould be chosen to reflect the amount of detailrequired. Layer numbering, line types andsymbols shall be in accordance with the CivilEngineering Department standard. Thehorizontal accuracy of the services surveyed byelectronic radio-detection shall be to ± 250mm,with vertical accuracy to ±100mm. Whereservices are located by trial pits they shall besurveyed to an accuracy of ±5mm horizontallyand vertically.

Location of services lines are to bedetermined by the co-ordinate of pointsalong the lines.

Co-ordinates may be derived frommeasuring:

Topographical SurveysTopographical surveys for CED Roads projectsare subject to CED Survey Unit review andapproval.

As-built SurveysAs-built drawings are prepared by contractorswith the assistance of supervising consultantsand private survey companies. They arerecorded in digital and map sheet form and arearchived in the CED Prime Document Storage.

a)

b)

c)

angle/bearing and distancefrom known control points.offset and chainage fromknown/co-ordinated lines (eg.road centreline)distances from 2 or moreknown points.

As-built surveys are reviewed by CED SurveyUnit on an ad hoc basis as required.

A3 SURVEY WORK PROCEDURES

In order to maintain consistency betweenprojects, specific procedures are to be followedin surveying, recording and presenting surveyinformation for highway design projects.

Typical survey requirements for highway designprojects are listed below.

A3.1 Topographical Surveys

The topographical survey shall cover the fullextent of the works to be designed and includetie-ins to all existing features.

Survey data recorded shall be sufficient toenable preparation of survey drawings and shallbe prepared in accordance with the specificationgiven in AS.

January 1997

• Level shall be recorded on the surveyplans to national datum at specificpoints along utility routes. Points shallbe levelled and recorded at bends,junctions and at 25m intervals alongstraights.

All radio-detection survey operators shall beapproved by the Civil Engineering Departmentprior to commencement of the services survey.

The results of radio-detection surveys shall becorroborated by manual excavation of trialholes at selected sites In accordance withservice authority procedures.

A3.3 As-built Surveys

On completion of construction, as-built surveydrawings shall be produced by the projectcontractor.

As-built utility information shall be collectedduring site works by the contractor andrecorded in digital format for line and level by

PageA/S


A5.2 Preparation of Survey Data

The Contractor shall prepare and submit thedata observed as survey plans in the followingformat:

For road corridors, cross section levels to theedge of the reservation or agreed extent shallbe taken at 25m intervals.

In addition, the data collected and surveyprocedures used shall be submitted in thefollowing format:

the supervising consultant. All as-builtinformation shall be collected in a digital formatcompatible with CED's highway design anddraughting software.

As-built survey drawings of principal alignmentsand visible features shall cover all of the worksinstalled under the contract including utilities,services and all finished alignments and levels,both above ground and subsurface.

As-built surveys shall be undertaken bycompanies approved by the General SurveySection and shall be in the format approved bythe Civil Engineering Department. Theconstruction contract is not normally consideredcomplete until the as-built surveys have beensubmitted to CED and approved.

A.4 APPROVED SURVEY COMPANIES

The General Survey Section is responsible forthe approval of survey companies in Qatar forcadastral survey work.

Companies undertaking topographical surveywork for road designs shall also be from theGSS approved survey company list.

A5 SPECIFICATION FORTOPOGRAPHICAL SURVEY

A.5.1 Features to be Observed

The survey contractor shall undertake a detailedtopographical survey of the subject areas. Thefollowing features shall be observed:

Building extents (including overhangs,walls, fences, gates and entrances)Kerbs, bitmac edges, tracks, footpathsand parking areasService posts/poles (eg. telephone,electricity, lighting, signals)Road signs (street names, traffic) andbillboardsManholes, gullies, hydrants, culverts,service boxes and markersOverhead and buried cables/linesTrees, plant boxes, landscaping limitsWater channels, culvertsSurface type changes (eg. betweennatural ground and concrete paving)Slopes, escarpmentsSpot levels at every 25m and at:a. Gates and entrancesb. Services covers, gullies, culvertsc. Isolated high and low pointsd. Abrupt grade changes.

January 1997

•

•

•

•

•

•

•

•

•

Topographical survey drawings shallbe produced at 1:500 scale for urbanareas. Larger scales of 1:200 or 1:100shall be used for areas requiringgreater detail such as major junctions.In rural areas, where few features arepresent, the survey drawings shall beproduced at 1:1000 scale or asotherwise agreed

Surveys plans shall be contoured at0.5m vertical intervals. Additional spotlevels shall be indicated at low andhigh points and across flat areaswithout contours

Levels at 25m intervals shall beindicated on the survey drawings. Inlarger open areas a grid of levels at25m centres can be used

AutoCAD" .DWG or .DXF plot file ofthe topographical maps

Printout of Easting, Northing, Level,and Code of all points

Comma-delimited DOS text file ofpoints containing:a. Point Numberb. Eastingc. Northingd. Levele. Code

Printout of raw data for thetopographical survey

Field data, computations anddescriptions for new controlstations/benchmarks

Job Report describing the workundertaken which includes:a. Location and project limitsb. Dates of survey

Page A/6


c. Methods and instruments usedd. Details about new control

points/benchmarks, whereestablished.

All digital data shall be submitted on 3.5" floppydisks.

AS.3 Specifications

The Contractor shall comply with the followingspecifications:

APPENDIX A

For multi-sheet drawings, sheet limitsshall be plotted with the current sheethighlighted.

5. Survey Drawing

All surveyed features shall be plotted.Lines shall be labelled when notspecifically identified in the Legend,(Table A5.4). Point features shall berepresented by standard symbols andannotated accordingly.

•

•

•

•

Survey works shall be tied to the QatarNational Grid and Height Datum or theQND95 co-ordinate system.

Establishment of new control stationsand benchmarks shall be in accordancewith Section 2 of the "Qatar SurveyManual". Levelling closure errors mustbe better than 15mm .fK, where K is thelength of the level route in km.Traverses shall have relativeaccuracies of 1/25,000 or betterEastings, northings and levels of detailpoints shall be within 10mm accuracy

Topographical maps shall be of theformat shown in Figure A5.1 and shallcontain the following information:

1. Project Details

North point symbol and grid coordinates shall be plotted such that nopart of the drawing is written over.

For multi-sheet draWings, match linesand appropriate notes for adjoiningsheets shall be provided.

Layers shall be used in the preparationof digital drawings. Each layer shallcontain only one feature type and shallbe appropriately named in accordancewith the typical layering given in TableA5.5

AS.4 Checking and Verification

All works and resulting survey data shall besubject to the checking and approval of theCED Survey Unit.

Contractor's name, projectnumber, surveyor's name,survey, sheet contents,number, plan scale.

2. Notes

referencedates ofdrawing

Details relevant to the survey workdone (eg. reference system, datum,methods and equipment used).

3. Legend

Listing of line types, symbols and codesused and corresponding descriptions.Tables A5.1, A5.2 and A5.3 liststandards for CED survey drawingswhile Table A5.4 is a typical legendlisting.

4. Location/Sheet Index Map

Drawing (typically at scale 1:10,000)showing the area surveyed, name ofmajor roads/streets, grid markers, coordinates and north point symbol.

January 1997 PageA/7

c.. "Tl

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Border (O.5mm. thickness) 20mm. (min.)

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Line Description Use

Standing kerb line, step, planter, concreteSolid line paving, SIS limit and other features not

otherwise listed.

Solid line, a.25m Cadastral plot boundary

Solid line, a.35m Building line

Two solid lines Wall (line separation equals thickness of wall.

----------------- Short dashes Edge of bitmac, flush kerb, change of surface

,---------_..._--_..- Short dashes, a.35m Building overhang

................... Dots Top/bottom of bank, change of grade

A' 1/ it .- Solid line and slash Picket fence, railing, crash barrier

_._._._.- Dash-dot Road Centreline

------- Long dash-short dash Overhead cable/line

0_"_"-,,-,,- Long dash-dot-dot Underground cablelline

All lines are a.2mm, thick unless otherwise specified

Table A5.1 - Survey Map Line Types

Symbol Description Use

c:=-<::J Scaled size Gate (length equals gate width)

Box, 1.2mm.squareU/G cable/duct marker, services and fire

0hydrant covers not more than a.5m.square

Clrcle,1.2mm.diameterBorehole, gully and circular MH cover not

0more than a.5m. diameter

0 Solid circle,1.2mm.diam. Bollard, marker post not more than a.5m.

• Solid box,1.2mm.square diameter

'" Triangle, 1.2mm.sides Triangular MH, sides not more than a.5m.

Services post/pole (electricity, telephone, street0 Solid circle, 2mm.diam. lighting, traffic signal); road sign and

sign board supported by single post

.. Solid box, 2mm.squareElectricity junction/traffic controller box and

telephone booth not more than 1m.square

&. Double triangle, 1.2mm. Survey control or benchmark

* Scaled size Palm tree

0 Scaled size Tree, general

To be drawn using a.2mm.pen

Notes: 1. Features exceeding prescribed dimensions shall be surveyed as polygons and plotted

with solid lines a.2mm. thick.2. Signs supported by more than 1 post shall be plotted as solid lines a.2mm. thick.

Table A5.2 - Survey Map Symbols



Annotation Description

B - Bollard

BH - Borehole

CB - Cadastrai boundary

EP - Electricity post

FH - Fire hydrant

G - Gully

GV - Gas valve

IC - Inspection chamber

JB - Electricity junction box

LP - Lamp post

MH - Manhole; type unknown

MHO - O-Tel manhole

MHS - Sewerage manhoie

MP - Marker post

PB - Post box

PC - Pipe culvert

PPB - Pedestrian push button pole

RS - Road sign (street name)

SIS - Electricity sub-station

SB - Sign board

SC - Stopcock

SM - Underground service marker

SV - Sluice valve

TCB - Traffic controller box

TEL - Telephone booth

TP - Telephone post

TSP - Traffic light/signal post

TS - Traffic sign post

WT - Water tank

WV - Water valve

APPENDIX A

Notes: 1. Annotations shall be plotted alongside corresponding symbol, line or polygon inthe drawing area and listed with appropriate description in the legend section.

2. The following features shall be additionally annotated with heights:-MH covers -Top and bottom steps-Guliies -Pipe culverts-Gates and entrances

Table A5.3 - Survey Map Annotations

January 1997 Page A/10


LEGEND'

: I : ,,'

c::--=:l

Jj,

*oB

BH

CB

EP

FH

GGV

ICJB

LP

MH

MHO

MHS

MP

PB

PC

PPB

RS

SIS

SB

SC

SM

SV

TCB

TEL

TP

TSP

TS

WT

WV

14.55

Table A5.4 - Typical Survey Map Legend

January 1997

APPENDIX A

Kerb line, unless otherwise specified.(Level taken at the channel)

Cadastral plot boundary

Building line

Wall

Edge of bitmac, unless otherwise specified

Building overhang

Top/bottom of bank

Picket fence, railing, crash barrier

Road centreline

Overhead cable/line

Underground cable/line

Gate

Survey control or benchmark

Palm tree

Tree, general

Bollard

Borehole

Cadastral boundary

Electricity post

Fire hydrant

GUlly

Gas valve

Inspection chamberElectricity junction box

Lamp post

Manhole; type unknown

O-Tel manhole

Sewerage manhole

Marker post

Post box

Pipe culvert

Pedestrian push button pole

Road sign (street name)

Electricity sub~station

Sign board

Stopcock

Underground service marker

Sluice valveTraffic controller box

Telephone booth

Telephone post

Traffic IighVsignal post

Traffic sign post

Water tank

Water valve

Spot height

Page A/11


LAYER NAME DESCRI PTION I FEATURES COVERED

BUILDING Buildings, houses, shops, bus shelters and corresponding levels

CADASTRL Cadastral points and boundaries

CONTROLS Control stations and bench marks

EX_ROAD Kerb lines, edge of bitmac, islands and corresponding levels

EX_WORKS Excavations, boreholes, temporary construction fences

GATES Gates and threshold levels

IMPROVEM Man-made features and corresponding levels not related to specific layer

e.g. steps, gardens, drinking fountains, private plant boxes, etc.

NATURAL Trees, waterways, vegetation limits

SERVICES Electricity, water, telephone and other services, and corresponding levels,

includes: manholes, gullies, hydrants, inspection chambers, valves,

electricity and telephone poles and lines, electricity sUb-stations,

junction boxes, postboxes, culverts, ducts, pipelines, services markers

SPOT_HT Spot heights and levels not related to specific layer

ST_FURNI Lamp posts, street name posts, sign boards, marker posts,

public plant boxes; and corresponding levels

TRAFFIC Sollards, traffic signal posts, vehicle detectors, pedestrian/road

markings, crash barriers, railings; and corresponding levels

WALLS Property walls and fences, and corresponding levels

CONTOUR 1 Major contour line

CONTOUR 2 Minor contour line

DESC_TXT Labels and annotations not related to specific layer

GRIDSDAT Map grid lines and coordinates

MATCHDAT Match lines and match line symbols and texts

PLANFORM Drawing margins, legend, title boxes, location map, notes

ROAD_DES Designed road IP's, center lines and reservations

Table A5.5 - Typical Layers for Topographical Survey Drawings


QATAR HIGHWAY DESIGN MANUAL APPENDIX B

APPENDIX B GUIDANCE NOTES TO PREPARE A BRIEF FOR GEOTECHNICAL SITEINVESTIGATIONS

This Appendix primarily is to assist the CEDEngineer in the preparation of a brief for ageotechnical site investigation.

The guidelines within this Appendix provide achecklist of items to be considered in theprocess of preparing a brief. A flow diagramidentifying the main points is shown in FigureB1.

B1 INTRODUCTION

Select Route

~Locate Junctions

,J,Locale Structures

+-Walkover/Drive

Sites

•Data Review

•Review StructureLocations

+Prepare Site

Investigation

+Decide on the

InformationRequired to

Enable Design

~Select the Investigation Procedures

Required 10 Provide the Information toEnable Design

J,Review the Scaleand Quantify the

Investigation

+Finalize Site

Investigation Brief

Each of the items listed in Figure B1 isdiscussed in the foliowing sections.

The approach to preparing a brief for concept ordetaiied design is the same. However, thetype of information required and size ofinvestigation varies. The different requirementsof both concept and detaiied design areidentified in the text.

It is essential that all works and specificationscomply with the most up to date versions of theCED approved documentation and procedures.

B2 INITIAL CONSIDERATIONS

Before preparing a geotechnical brief theEngineer must consider the foliowing:

Route SelectionIn Qatar it is often the case that the routecorridors are predetermined by the PlanningDepartment. However, the engineer shouldreview the selected route following goodpractice and guidance given in the QatarHighway Design Manual. The engineer shouldat this stage be confident that it is feasible toproduce a compliant road design within theroute corridor provided.

Locate JunctionsThe junction locations are likely to be dictatedby one or more of the following:

• Existing or proposed routes

• Existing or proposed developmentssuch as villas, shops or petrol stations

• Service equipment such as electricitypylons, substations, pumping stations,cables or pipelines

• Geotechnical conditions.

The geotechnical investigation may revealground conditions which result in moving thejunction or changing the design. Junctionsoften invoive some form of structure, forexample, a full grade separated interchange oran ornamental structure in the middle of aroundabout. So the geotechnical information isquite likely to have a bearing on junctionlocation.

Figure B1 Preparing a Geotechnical Brief

January 1997 Page B/1


Locate StructuresThe types of typical structures to be found onhighway works are:

• Bridges

• Embankments

• Cuttings

APPENDIXB

B3 PREPARATION OF THE BRIEF

Following the initial considerations (referSection B2), the engineer must then decide onthe information required in the design process.Details of the various methods of investigationand testing listed below are discussed inSection B4.

••

Traffic Signals, Signs and Lighting

Box Culverts

B3.1 Geotechnical Investigation Works

The following investigation works may berequired:

• Underpasses

• Ornamental Structures such as Archesand Feature Structures inRoundabouts.

Before preparing a geotechnical brief theengineer should have a full understanding ofthe outline design and be able to identify thetype, approximate location and scale of thestructures to be built. These are importantfactor in defining and quantifying the siteinvestigation, as most of the investigation willbe concentrated at the location of thestructures.

Walkover/Drive SiteHaving determined the route and location of thejunctions and structures, the engineer shouldthen visit the site. The site should be walkedover or driven through, depending on the scaleof the project. The purpose of the site visit is toget a visual impression of the route, locate thejunctions and structures and identify anyobvious anomalies which may have a bearingon the project. For example a drive through asite may identify lush green vegetation in lowareas indicating possible groundwater. Thismay require additional site investigation toconfirm the problem. The site investigationreport should identify such topographic featuresand, as a result of the testing, advise of anyproblems relating to the design and of anydifficulties which may arise during theconstruction period.

Data ReviewFollowing the site visit, the Engineer shouldreview the site notes and, if necessary, amendthe design accordingly. Any problem areasshould be highlighted and these notes referredto when preparing the site investigation brief.The location of structures should be reviewedagainst the site visit notes so that if a potentialproblem exists, either the location is changed,the design of the structure is modified or thesite investigation brief increased to cover anyadditional investigation works.

January 1997

• Desk Study

• Geotechnical Walkover

• Trial Pits

• Boreholes

• Samples

• Field Tests

• Laboratory Tests.

Each of the above works is described in SectionB4 of this Appendix.

Schedules for Geotechnical InvestigationsThe following tables quantify typicalgeotechnical investigations for the followingconditions:

• Roads· Feasibility Stage, Table B1

• Roads· Detailed Stage, Table B2

• Structures· Feasibility Stage, Table B3

• Structures· Detailed Stage, Table B4.

The schedules give advice on the frequency ofdifferent methods of investigations. Thesenotes are merely guidelines to be used in thepreparation of a brief. Each site investigationbrief should be considered on its own merits,taking into account the purpose of theinvestigation, stage in the design process, scaleand design of the project and its location.

Page B/2

QATAR HIGHWAY DESIGN MANUAL APPENDIXB

Road Description Notes

Dual 2-3 Lane Trial Pits: Trial pits should be located at 1aDOrn spacing. It is important to ensure that the proposedSingle 2 Lane The trial pits should not all De located solely along the road does not interfere with the hydrology of

centreline but should be spread over the width of both the area. Note should be made of anycarriageways or the corridor. Trial pits should be groundwater in the trial pit and anyconcentrated at identifiable problem areas. Trial pits evidence of collecting water in the areawould typically be up to 2.5m deep. such as evaporation salts or green grass in

low areas.Boreholes: These may be considered necessary if thedesk study reveals a problematic area. Borehole In built up, urban areas, special attentionquantities and locations should be reviewed by a should be given to locating the trial pits toGeotechnical Engineer, however, the investigation should avoid services such as electricity, water orbe concentrated in the problematic area. Q-Tel.

Laboratory Testing: Testing should be undertaken ofsamples at each trial pit and borehole. This frequencyshould be reviewed by the Geotechnical Engineer on siteand the scope reduced or increased as necessary.

Table B1 Schedule of Geotechnical Investigations for Roads at Feasibility Stage

Road

Dual 2-3 LaneSingle 2 Lane

Description

Trial Pits: Trial pits should be located at 500m spacing.The trial pits should not all be located solely along thecentreline but should be spread over the width of bothcarriageways. Trial pits would typically be up to 2.5mdeep.

Boreholes: Boreholes should be located at 1kmintervals. If the desk study reveals that consistent rockand soil conditions are to be expected, the number ofboreholes may be reduced to suit.

Permeability Tests: Falling head or constant headpermeability tests undertaken in boreholes located at 1kmintervals or in areas of differing ground conditions wheresurface water from the highway will require collection anddischarge.

Dynamic Cone Penetration Tests: Where the desk studyor walkover survey reveals that soil conditions such assabkah or alluvium are present, then DCP testing shouldbe considered in these areas, typically at 200m centres.

Laboratory Testing. Testing should be undertaken ofsamples at each trial pit and borehole. This frequencyshould be reviewed by the Geotechnical Engineer on siteand the scope reduced or increased as necessary.

Notes

It is important to ensure that the proposedroad does not interfere with the hydrology ofthe area. Note should be made of anygroundwater in the trial pits and anyevidence of collecting water in the areasuch as evaporation salts or lush greengrass in low areas.

In built up, urban areas, special attentionshould be given to locating the trial pits toavoid services such as electricity, water orQ-Tel.

Table B2 Schedule of Geotechnical Investigations for Roads at Detail Stage



Structure Description Notes

Interchange Boreholes: At least one borehole to be located at each Trial pits alone are not sufficient for majorproposed abutment position.· The borehole should locate structures.rock head and penetrate 5m into rock. Where rock is notpresent, the borehole should extend a minimum of 1.5 Structures in the urban location may havetimes the width of a shallow foundation. If piled the benefit of other geotechnicalfoundations are anticipated, the borehole should extend investigations carried out in the vicinity andto rock plus Sm.. A local geotechnical expert can advise so the scope of investigation works may beon anticipated depths for various locations in Qatar. reduced.Groundwater shall be recorded if present. If groundwateris likely to be a problem, it is recommended that the waterlevel is monitored over a period to allow for seasonalvariation.

Trial Pits: It is advisable that trial pits be located onselected slip roads and tests undertaken to determine theparameters required to design the earthworks, seeEmbankment below. Trial Pits would typically be up to2.5m deep.

Box CUlvert Trial Pits: At least one trial pit to be located at the Usually in rural locations, it is important toproposed culvert position. Trial Pits would typically be up review topography and hydrology to locateto 2.5m deep. the culvert.

Embankment Boreholes: For embankments/cuttings 2.5m high/deep If the cutting is deep, the engineer should!Cutting or greater, at least one borehole to be located at the consider the stability of the slopes.

proposed embankment/cutting position. If the Boreholes should therefore be staggeredembankment/cutting is very long, boreholes should be across the cutting and not just follow thelocated every kilometre. Boreholes should extend at least road centreline. Laboratory tests should3m beneath the level of the bottom of the proposed identify parameters for slope stability andembankment/cutting. Boreholes should identify rock head settlement to verify that it is possible for anand record groundwater if present. Standard penetration embankment/cutting to be bUilt.tests are usually recommended to determine hardness.

Trial Pits: For embankments/cuttings less than 2.5mhigh, at least one trial pit to be located at the proposedposition. Trial ~its would typically be up to 2.5m deep.For cuttings, investigations should extend a minimum of2m below cutting base level, or to rock. As such, trial pitsmay only provide information regarding the material to beexcavated.

Special Site investigations for special structures such asStructures ornamental arches, roundabout centre pieces, gantries or

cantilevers for traffic signs will require individualconsideration depending on the size of the structure andits location.

Table B3 Schedule of Geotechnical Investigations for Structures at Feasibility Stage



Structure

Interchange

Box Culvert

Embankment/Cutlings

SpecialStructures

Description

Boreholes: At [east four boreholes to be located at thesite of a typical interchange in addition to those takenalong the main carriageway through the interchange.

Boreholes should locate rock head and typically penetrate5m into rock or 5m below formation level, whichever is thedeeper. Groundwater shall be recorded if present. Ifgroundwater is Ilkely to be a problem, it is recommendedthat the water level is monitored over a period to allow forseasonal variation.

Plate Bearing Tests: Test to be carried out at foundationlevel for all fou(ldation locations on the advice of thegeotechnical expert.

Permeability Tests: Falling head or constant headpermeability tests to be undertaken in boreholes.Necessary where surface water from highways will requirecollection and discharge.

Trial Pits: It is advisable that trial pits be located on eachslip road and tests undertaken to determine theparameters required to design the earthworks, seeEmbankment below. Trial Pits would typically be up to205m deep.

Trial Pits: At least one trial pit to be located at theproposed culvert position. Trial Pits would typically be upto 2.5m deep.

Plate Bearing Tests: Test to be carried out at foundationlevel for all foundation locations on the advice of thegeotechnical expert.

Boreholes: Depending on the findings of the FeasibilityInvestigation it may be necessary to locate a borehole atthe culvert position. Boreholes would typically beextended to 3m below the foundation level.

Boreholes: For embankments/cuttings 2.5m high/deepor greater, at least one borehole to be located at theproposed embankment/cutting position. If theembankment/cutting is very long, boreholes should belocated every kilometre.

Boreholes should typically extend at least 3m beneath thelevel of the bottom of the proposed embankment/cutting.Boreholes should identify rock head and recordgroundwater if present. Standard penetration tests areusually recommended to determine relative density.

Trial Pits: For embankments/cuttings less than 2.5mhigh, at least one trial pit to be located at the proposedposition. Trial Pits would typically be up to 2.5m deep.

Site investigations for special structures such asornamental arches, roundabout centre pieces, gantries orcantilevers for traffic signs will require individualconsideration depending on the size of the structure andits location.

Notes

Trial pits alone are not considered sufficientfor major structures.

Structures in the urban location may havethe benefit of other goetechnicalinvestigations carried out in the vicinity andso the scope of investigation works may bereduced.

Depth of borehole to extend 5m belowdepth of proposed foundation.

Usually in rural locations, it is important toreview topography and hydrology to locatethe culvert.

Laboratory tests should identify parametersfor slope stability to verify that it is possiblefor an embankment/cutting to be built (BulkDensity determines air/water voids, ShearStrength determines bearing capacity).

Note. The chOIce of borehole depth should be at least to the depth of the extent of the pressure bulb set up by the foundation.The final decision on whether to continue the borehole further should be made by the geotechnical engineer on site.

Table 84

Notes

Schedule of Geotechnical Investigations for Structures at Design Stage

1 Whilst detail design information is not usually required at the early stages, it is better to provideas much geotechnical information as possible, as early as possible.

2 Care should be taken when locating boreholes and trial pits, to ensure that services are notdamaged during the investigation. This is particularly important in the urban situation.



B3.2 Field Tests B3.3 Laboratory Tests

Field tests to determine the density, bearing orshear strength of in situ materiai are veryvaluable as they can be carried out withoutdisturbing the soil.

Laboratory testing will be required on thesamples taken. Table B6 lists the most·commonly used laboratory tests and givesgUidelines on the frequency of testing. Thetests are discussed in Section B4.

Note. Tests should also be mcluded at changes of strata.

Whilst each testing programme must be tailoredto suit the particular site investigation, Table B5gives guidelines on the frequency of testing forthe most commonly used tests.

The testing frequency given in Table B5 isshown as a guideline. It is common practice forthe schedule to be revised by the geotechnicalengineer responsible forthe site investigation asthe investigation proceeds.

Test Notes Frequency

Standard Cohesionless soils 1m intervalsPenetration throughoutTest depth of

borehole

Unconfined Gives shear stress of If cohesiveCompression soil soils. 1mTest intervals

throughoutdepth ofborehole

California In situ used as a 2 tests perBearing Ratio guide for pavement trial pit

design. QHDM uses Iboreholelaboratory CBR fordesign.

Standpipe Monitoring water I test perPiezometer levels borehole with

regularmonitoring

Plate Bearing Used in foundation 1 test atTest design to determine each major

ground bearing structurepressure

Shear Vane Measures shear If cohesiveTest strength of soft soils soils. 1m

intervalsthroughoutdepth ofborehole

Permeability Used to determine 3 test perTest permeability rates for borehole

soakaway design

In Situ Measures density of If cohesiveDensity Test soils soils. 1m

intervalsthroughoutdepth ofborehole

Schedule for Laboratory Tests

It may not be necessary to carry out ali thetesting listed in Table B6. The engineerresponsible for preparing the brief may decideto reduce the scope depending on theinformation he needs for the design.

Table B6

Test Notes Frequency

Atterberg Plasticity index, 2 tests perLimits liquid limits trial pit

/borehole

Particle Size Used in grading 2 tests perDistribution and classification trial pit

of material /borehole

California Used for pavement 2 tests perBearing Ratio design. Shall be trial pit

carried out in Iboreholeaccordance withQCS.

Chemical pH. Sulphate & 1 tests perTests Chloride, Used to trial pit

check compatibility /boreholeof materials andaggressiveness ofground and wateron concretestructures,

Dry Density / Essential for slope 2 tests perMoisture stability in trial pitContent embankments/ IboreholeRelationship cutting

Moisture Essential for all 2 tests perContent and testing regimes - trial pitDensity relates sample to Iborehole

liquid and plasticlimits

Triaxial Determines shear If suitableCompression strength for samplesTest cohesive soils recovered

Unconfined Gives shear stress If suitableCompression of soil samplesTest recovered

Point Load Determines ground 2 tests atTest bearing pressure selected

(for rock only) boreholes

Schedule for Field TestsTable B5



B4 ENGINEERING CONSIDERATIONS

B4.1 Methods of Investigation

When discussing the procedure forinvestigation, reference was made to borings asa means of investigation. This is perhaps themost common method of site exploration, butcertainly not the only one. BS 5930: 1981 Codeof Practice for site investigations providesdetails of investigation methods to assessground conditions for construction purposes.Considering new works, from very small to verylarge contracts, a general guide to explorationwould be as follows:

• Small works - trial pits up to 3.0m deep

• Medium to large scale works - boringsup to 30m deep, typically 20m

• Very large scale works (e.g. gradeseparation and dams) - a combinationof deep borings and pits.

It must be noted that the above is only a guide,the detailed methods of exploration woulddepend on the type of construction and siteinvolved.

Where rock is expected, borings of varioustypes should be used unless a number of pitswould prove more economical. In soils, thenormal method of exploration is by boring holes(unless the loads expected are small, thenshallow pits will provide adequate samples fortesting).

The cost of setting up drilling rigs on site variesfrom area to area depending on transportationcosts.

Before an estimate can be established for siteinvestigation work, the number of boreholesand types of test must be determined. This willbe dependant on how much information isalready available.

B4.1.1 Trial Pits

This is the cheapest form of exploration inshallow depths (e.g. up to 3m). Above 3metres deep, the cost increases rapidlycompared with boring. The main advantage isthat soils and rocks can be exposed andexamined in situ. This method shows changesin strata much more clearly than by borings.The pits are dug out either by local labour or bya small tractor-mounted excavator. The plansize of a pit depends on method of excavation,

January 1997

APPENDIX B

but approximately 1.2 x 1.2 m should be dug.Holes should be kept well clear of the positionof actual foundations, but should be in thevicinity of important structures such as heavilyloaded walls or columns.

Problems occur in water-bearing soils,particularly sands, and therefore the economiesof shoring and pumping pits may outweigh thesavings gained against specialist borings. Indry conditions, these pits are particularlyvaluable since they allow hand-cut samples tobe taken, thereby minimising the disturbance ofthe sample and maximising the conditions foraccurate testing.

Deeper trial pits may be used in theinvestigation of rock fissures or to explorelayers of weak rock which cannot be removedintact in normal boring operations. Such deeppits are costly to construct and would be usedonly in large scale exploration.

Trial pits are often the best method of exploringback filled areas and sites overlain by variablenatural deposits.

B4.1.2 Boreholes

This type of exploration can be achieved byvarious methods:

Hand or mechanical auger borings arerelatively cheap methods of sub-surfaceexploration of soils which will standunsupported. Hollow stem augers can be usedto support soils in borings. Holes can be sunkto depths up to 30 metres provided there are noobstructions such as boulders. The diameter ofthe borehole is usually>1OOmm. This allowssoil sampling tubes to be used without difficulty.The mechanical auger is used in gravelly soil,which involves the use of a casing to preventcollapse of the boring.

Percussive boring is a method which can becarried out in all types of soils, because theborehole is lined with a thick-walled steelcasing. The boring is achieved by using openended shells in cohesive soils and clack valvesin cohesion less soils.

Other tools include chisel bits for breaking upboulders. All the tools and sampling tubes areattached to sectioned rods.

Page B/7


If the walls of the borehole require support, theborehoie is lined as the hole is bored and thesection iinings screwed together and driven asthe hole deepens.

Percussion boring is the oldest method ofboring, in which the formation is broken up byrepeated biows from a bit or chisel. Water isadded to the hole as the work proceeds and theresulting debris is removed at intervals by shell,auger or pressure washing. Samples from thistype of boring are inevitably disturbed. A newsystem using a compressed air hammerprovides a quick method of boring forpermeability tests. This method does notfaciiitate core sampiing.

Rotary coring, which is used for the explorationof rocks, can be divided into twG categories:

Core DrillingCore driliing is a process designed to recovercontinuous cores of rock. Water orcompressed air is jetted down the hoie throughhollow rods and returns up the annular spacecarrying rock cuttings from the coring bit. Forhard rock cores, the crown of the drill is usuallytipped with industrial diamonds. The continuouscores are laid in wooden core boxes in depthorder.

Mud-rotary DrillingIn mud-rotary driliing, a mud-laden fiuid ispumped in a continuous stream down hollowdriliing rods to the rotating bit. The bit is kept incontact with the face of the boring and the fiuidcarries the debris up the annular spacebetween the rods and the sides of the hole. Asteel casing to the hole is not necessary. Thecores are obtained by the use of coring tools.This type of drilling is not normally used for siteinvestigation work.

APPENDIXB

In boring operations, it is common practice toobtain 'bulk' disturbed samples in order toobtain sufficient sample for compaction andCBR tests, together with full gradings if the soilis granular in nature. This is particularlyappiicable if the bore is penetrating a proposedcutting.

Undisturbed samples: these are samplesremoved by methods which preserve, so far aspracticable, the natural structure and propertiesof the material. Samples in this category areeasily obtained in rock and clay, but difficult incertain other soils. Table B1.1 show themethod employed for obtaining samples.

SAMPLING METHOOS

Disturbed Hand samplesSoil Auger samples

Shell samnles

Undisturbed Hand samplesCore samDies

Disturbed Sludge samples fromRocks oercussion or rotary drills

Undisturbed Hand samples, cores

Table B1.1 Sampiing Methods

84.2 Testing

For any particular location, the engineer mustfirst estabiish the depth and classification ofeach strata of subsurface material andcompare this with what was envisaged. To dothis, a range of tests will be required.

Having compieted the tests and reviewed theresults, the engineer should consider whetherthe investigation has confirmed his initialassumptions or whether if has introduced newproblems.

84.2.1 In Situ Testing

Tests to obtain the density or shear strength ofsoils in situ are very valuable since they can becarried out without disturbing the soil. Suchtests are particularly valuable in sands andsilts. The main tests are:

Cone Penetration TestsWhere a significant thickness of unconsoiidatedoverburden is know to exist, Static 'Dutch' ConePenetration tests could be conducted to asuitably agreed depth. Methods and equipmentin accordance with BS 5930.

B4.1.3 Samples

There are two types of sample.

Disturbed samples: these are samples removedfrom boreholes with augers or other equipmentwhich interfere with the natural structure of thematerial. Such samples are usefui for visualgrading and determining moisture content, andin some cases for laboratory testing. Samplesare placed in airtight jars with identifying labels.

January 1997

•••••

Standard penetration

Unconfined compression

California Bearing Ratio (CBR)

Monitoring water levels

Plate bearing test

Page B/8


.. Shear vane test

.. In situ density test

.. Permeability test.

Standard Penetration TestAs with all penetration tests, this consists ofmeasuring the resistance of the soil topenetration under dynamic loading. Thisparticular test is made by driving a 35mm(internal diameter) split spoon sampler into thesoil at the bottom of a borehole. The sampler,suspended on rods, is first driven 150mm intothe soil by a falling standard weight (63.5 kgfalling through a distance of 760mm). Thesampler is then driven a further 300mm and thenumber of blows needed to achieve this isrecorded as the 'N' value. The test is used toestablish the relative density of soil, and forparticular soils to design foundations and gaugesettlement.

California Bearing Ratio TestThis test may be used in the design of flexiblepavements and can be carried out on site. Thetest shows the load-penetration of soils relativeto a standard crushed stone sample. The testis normally carried out on soil at least 1m belowground level (i.e. below the level of anyseasonal moisture fluctuation) using a lorry toobtain the necessary reaction load through ascrew jack.

The in situ CBR test provides a different resultto that obtained in the laboratory under similarconditions of density etc. Road design isnormally carried out based on the laboratoryCBR only.

Standpipe PiezometerMonitoring of water levels is carried out by theuse of piezometers. If a borehole is to beconstructed to obtain soil information, thenunless circumstances dictate otherwise, itshould be utilised in order to monitor thefluctuation in ground water level. This may becarried out for several years depending on thetime scale of the project. Such information willbe invaluable in the future once general trendshave been established.

Plate Bearing TestThis type of test was once very popular and isstill used on large engineering projects as ameans of providing in situ data on thebehaviour of soils or rocks at foundation level.The procedure consists of excavating a pit tothe level of the proposed foundation and thenloading a steel or cast iron plate (usually 600 x600mm in size) on the bottom of the pit. The

January 1997

APPENDIX B

load can be applied in either of two ways; thefirst by loading it with increments of kentledge(concrete blocks or steel billets); the second bymeans of a hydraulic jack bearing against aheavily loaded beam.

Failure is traditionally assumed when thesettlement reaches a depth equal to 10%(some engineers say 15%) of the breadth of theloading plate, this should be verified by plottinga time/load/settlement graph. The safe load(qs) should be taken as one-third of that loadwhich causes failure or the failure load dividedby the project factor of safety. For moststructures, a generally accepted maximumallowable settlement is 25mm. Terzaghi & Peckhave proposed a relationship which enablesallowable bearing pressure to be calculatedbased on a chosen allowable settlement andthe load/settlement results obtained from aplate bearing test.

The plate bearing test is useful in stony soilswhere undisturbed sampling is difficult.However, care should be taken to ensureenough tests are taken to be representativewhere soils may be variable across a site.

The plate bearing test data can also be used tocalculate a soils modulus of subgrade reaction.

One disadvantage of this test is the lack ofsimulation of "bulb pressure". The bulbpressure from a test of this nature is usually farsmaller than the bulb pressure from the actualfoundation. This could lead to error indetecting settlement of a lower weak stratum.

Shear Vane TestThis test measures the shear strength of softcohesive soils in situ. The vane is pushed intothe soil and rotated by hand at a constant rate.The amount of torque necessary for rotation ismeasured by a spring balance on top of therods and the shear strength of the soil iscalculated.

In Situ Density TestTypically sand replacement or nuclear densitytests are undertaken in the field. Theseprovide the field density of soils and are usefulin assessing compaction and settlement.

Permeability TestThis test enables the permeability of the soil orbedrock to be ascertained. The most commontype of permeability test undertaken in Qatar isthe falling head test to BS 5930. However, thetype of test and the number per boreholeshould be agreed with the Civil EngineeringDepartment.

Page B/9


Dynamic Cone Penetrometer TestThis test utilities a hand held drop hammerpenetrometer which records cone penetrationresistance versus number of blows. Graphicalplots of results enable equivalent in situ CBRvalues of the ground to be determined.(Typically used for depths up to 2.0m). Refer tothe TRL specification for DCPT equipment andCBR correlation relationship.

Other TestsOther in situ tests include the handpenetrometer and hand shear vane.

B4.2.2 Laboratory Testing

Laboratory testing is undertaken to establishthe following characteristics of soils:

.. Identification and classification

.. Measurement of engineering properties

.. Chemical content.

Identification and ClassificationThis analysis involves a number of individualtests, such as:

Visual examinationMoisture contentLiquid and plastic limitsParticle size distribution.

Visual Examinations: made to note the colour,texture and consistency of disturbed andundisturbed samples, these being used later todescribe the soil in the engineer's reports.

Moisture Content: important in all soilsamples, since it helps to arrange a programmeof testing (by relating samples to liquid andplastic limits) so that no doubtful sample will beoverlooked. The higher the natural moisturecontent of the soil, the greater will be itscompressibility.

Liquid and Plastic Limit Tests: made oncohesive soils for classification purposes andfor assessing their compressibility. The liquidlimit (LL) (BS 1377 Test 3 and 4) determinesthe amount of moisture content necessary tocause the material to flow or move readilyunder a given number of vibrations, whereasthe plastic limit (PL) is determined by rolling outa 4 mm diameter thread of soil and noting themoisture content which will allow the thread tobe rolled out still further until it breaks up due todrying. When both liquid and plastic limits areknown, the Plasticity Index can be established(Plasticity Index = LL-PL).

January 1997

APPENDIXB

Particle Size Distribution: of particularimportance when assessing problems ofexcavation in permeable soils below the watertable. It is also useful for assessing the valueof non-cohesive soils for use as aggregatesand construction materials. The first part of thetest is achieved by sifting dried samplesthrough BS 410 sieves. In the case of cohesivesoils, a wet analysis is used, employing ahydrometer. The range of particle sizes iscompared with a standard chart. PSD is alsouseful for identification purposes andassessment of material suitable for use as fill.

Measurement of Engineering PropertiesThe foregoing tests give some indication of theengineering properties of a sailor rock, butthere are also specific tests which yield moredefinite information relating to:

Bulk density of soilShear strength of soilConsolidation of soilLaboratory CBRLaboratory compactionPoint load testingUnconfined compression testing(+deformation modulus)

Bulk Density: the weight of material per unitvolume, including the weight of air or water inthe voids. This information is essential in thedesign of retaining works, where the weight ofa stratum is an important factor (e.g. stability ofslopes, formation of earth dams, earth pressureof retaining walls etc). Dry density (weight ofsolids per unit voiume) is used for thedetermination of optimum compaction in earthdams, embankments and other soil structures,and in the laboratory CBR test.

Typically cone-cutter and sand replacementtests are carried out to determine bulk density.

Shear Strength: can be used directly tocalculate a soil's bearing capacity and also tocalculate the pressure on supports inexcavations. There are several tests availablefor ascertaining shear strength, but the mostpopular is the triaxial compression test. Triaxialcompression tests are suitable for cohesivesoils only. Where cohesion less soils have tobe tested, the shear box test is used. Asample of soil is subjected to a standard loadunder which a horizontal force is applied to thelower half of the box until the sample shears.

Page B/10


The Triaxial Compression Test can be carriedout using any of three different methods:

• Undrained

• Consolidated undrained

• Drained.

In principle, the test consists of subjecting acylindrical sample of undisturbed soil (75 mmlong x 38 mm diameter) to lateral hydraulicpressure in addition to a vertical load. This isachieved by placing the sample in a speciallydesigned plastic cylinder which is subsequentlyfilled with water. Both vertical and lateral loadscan be increased as required in order tosimulate the in situ stresses. Measurement ofthe forces needed to shear the sample is usedin the calculation of bearing capacity. In theundrained triaxial test (often referred to as thequick test) the sample, encased in a rubbersheath, is capped with non-porous end plates toprevent the pore water escaping and allow axialloading of the ends. Three tests are carriedout, one each on three samples (all cut from thesame large sample ), each being subjected to ahigher hydraulic lateral pressure before axialloading is applied. The results are then plottedin the form of Mohr's circles.

The consolidated undrained triaxial test allowsthe sample to drain while applying the hydraulicpressure, thereby allowing the sample toconsolidate. After consolidation the sample isstressed without further drainage.

In the drained test, the axial load is applied soslowly that the pore water can drain off.withoutbuilding up any pressure in the sample. Thedrainage continues throughout the test and theamount of water drained oft is measured. Inboth cases, where drainage is achieved, thewater passes through porous discs at the endsof the sample and then through ducts in theapparatus.

The consolidated undrained test and thedrained test have particular application to thebehaviour of soil in earth dams andembankments, and also to stability problems ingeneral.

Consolidation test: used to calculate themagnitude and rate of consolidation of aparticular soil. This is very important incalculating the movement of soil underfoundations. The apparatus used is called an'Oedometer'. The test consists of placing acylindrical sample (75 mm diameter x 18 mmthick) in a metal ring and capping with porousdiscs. The sample is placed in a water-filled

January 1997

APPENDIXB

tray and subjected to load. The load isincreased every 24 hours and a timesettlement curve is plotted. Again, this is onlysuitable for cohesive soils.

Laboratory CBR: shows the load-penetrationof soils relative to a standard crushed stone,(see Clause B4.1.3). The test is carried out ina controlled laboratory situation and is of greatimportance as it is laboratory CBR values thatare referred to in QCS and Section 9 Pavementof QHDM, and which construction materialsand subgrade should meet.

Laboratory Compaction: provides theoptimum moisture content for a soil sample.

Successive samples of soil are progressivelywetted and compacted in a mould. The drydensity/moisture content of these successivesamples is then plotted to find the optimummoisture content. Typically, the Proctor test iscarried out (in accordance with BS 1377)though the modified AASHTO and vibratinghammer techniques are also commonly used.

The value of optimum moisture for the soil isusefui for preparing a soil prior to sitecompaction in order to ensure minimumcompactive effort and specification compliance.

Results achieved are also used in otherlaboratory tests such as the CBR test.

Point Load Testing on Rock: involves thedetermination of failure strength of rock coresamples either by loading axially, diametricallyor irregularly. Refer to BS 1377 or ISRM(International Society for Rock Mechanics).

Unconfined Compression Testing (plusmeasurement of Deformation Modulus onRock): involves measurement of failurestrength and deformation characteristic ofprepared samples. This test can be used eitherin the site laboratory or in the field, since theapparatus is very portable. This method istherefore particularly useful where a largenumber of samples are required to be tested.Rock samples 75mm long and 38mm diameterare placed in the apparatus and an axial loadapplied. The sample is sheared under loadand the shear stress is automatically recordedon a chart fixed to the apparatus. Refer to BS1377.

Sedimentation Test: used to assess whethermaterial is a silt or a clay. Refer to BS 1377.

Laboratory Permeability: used to determinepermeability of reconstituted samples, egosubgrade or roadbase materials.

Page B/11


Miniature Shear Vane: carried out on boreholesamples of cohesive material. Commonly usedwhen samples are not suitable for other testing.

Chemical Content: a chemical analysis ofsoils, rocks and groundwater is carried out toassess the effects, if any, which theircomposition might have on any material to beused in the proposed works. The tests mainlycover sulphate and chloride content and pHval ue, although bacteriological analysis mayalso be required for works in tidal mud flats.

B4.3 Earthworks

Earth moving for roads takes place over arelatively narrow band of terrain and a balanceof cut and fill is often difficult to achieve.Constraints to the profile are imposed by theneed to provide required clearances for bridgesunder or over existing roads or to cross them attheir existing level.

Earthworks should be designed to provide anadequate safety factor for shear failure and toensure that any deformation is withinacceptable limits. The information requiredbefore the cross section of the embankmentcan be designed includes:

• Ultimate width of top of embankmentincluding median, shoulder and verge

APPENDIXB

shall all be in accordance with the QatarConstruction Specification.

The Ground Investigation Report shouldidentify the rock horizon for areas of cut, shouldsuggest methods of excavating the material,and should identify whether the material islikely to be suitable for use as a fill material.

B4.4 Retaining Structures

Where sufficient land width is not available toaccommodate the full width of the base of theembankment, the provision of earth retainingstructures has to be considered. Below is a listof some of the different types of earth retainingstructures commonly used.

• Gravity walls in mass concrete,brickwork or stone masonry

• Reinforced concrete walls,counterfortlbuttress

• Diaphragm walls

• Piling walls

• Crib walls

• Gabions

• Reinforced earth walls.• Loading on top of embankment

All imported fill material for a CED schememust be provided using the services of theQatar National Transport Office. The selectionof such material and its placing and compaction

In the design of approach embankments tobridges and other structures, thesuperstructures, substructures and associatedearthworks should be designed as a whoie andnot individually. For further reference onearthworks refer to British Standard 6031, Codeof Practice for Earthworks. The road designshould attempt to minimise earthworks. Theaim shouid be to balance cut and fillrequirements, allowing for rejection ofunsuitable material, bUlking and compactionfactors. This will avoid having to dispose of, orobtain large quantities of material.

•

••

Geotechnical properties of foundationand fill materials

Reservation width

Special considerations, ego tidal area,sound barriers, services etc.

Gravity WallsGravity walls are suitable if the soil in the lowerpart of the cutting can be cut back steeply to atemporary slope to allow the wall to beconstructed. Any space between the back ofthe wall and the temporary slope is thenbackfilled.

Reinforced Concrete WallsReinforced concrete walls are suitable if thesoil in the lower part of the cutting can be cutback steeply to a temporary slope to allow thewall to be constructed. Any space between theback of the wall and the temporary slope isthen backfilled. Alternatively, these walls canbe constructed in a timbered trench, the soil infront of the wall being removed after completingthe retaining structure.

Diaphram WallsDiaphragm walls, continuous bored pile wallsand secant bored piles are suitable for weak,unstable or heaVily water-bearing soils where atemporary steep slope cannot be formed orwhere construction in a trench would causeproblems of support or loss of ground.



B4.5 Geosynthetics

.. Reinforcement for subgrade and subbase materials in roads

Geosynthetics are extremeiy versatile and maybe used in the following instances:

Piling WallsSteel sheet piling may be used as a permanentretaining wall if consideration is given to somemeasure of protection against corrosion wherea very long life is required. Usually, however,sheet piling is used as a temporary supportduring the construction period.

Crib WallsPrecast concrete block walls or crib walls are aform of gravity section and may be economicalfor sites where suitable broken rock or gravel isavailable as a fill material for the cribs.

.. Line drainage facilities, ego wrappingaggregate around soakaways toprevent loss of fine materials, toseparate materials of different grade orplaced behind a retaining wall to act asa drainage medium

Gabion WallsGabions are suitable for sites where brokenrock, boulders or large gravel are available forfilling the wire mesh baskets and where spaceis available to arrange the baskets in tiers toform a stepped-back retaining wall. A very longlife is not possible with gabion walls, but plasticcovered galvanised wire mesh can providemany years of useful support. The flexibility ofa gabion retaining wall is advantageous forsites where appreciable deformation of a slopemay occur as a result of stress relief.

Gabions are partiCUlarly suitable forconstruction in conditions where earth slopesare temporarily or permanently flooded andsubjected to scour from flowing water.

Reinforced Earth WallsReinforced earth retaining walls can be formedin the lower part of a cutting siope byexcavating at the toe to form a temporary steepslope, then replacing the excavated soil incompacted layers of essentially granularmaterial, each layer being reinfQrced byhorizontai metal or plastic ties (refer to ClauseB5.3). The steeply inclined face of the retainingwall is protected by metal, reinforced concreteor plastic cladding elements. Reinforced earthretaining walls have the advantage of flexibilityand are suitable for soil conditions whereappreciable forward movement or heaving of acutting is anticipated as a consequence ofstress relief.

Consideration may also be given to the use ofground anchors or rock bolts. Information onmethods of design and construction of theabove types of wall can be found in the BritishStandard publications, BS 8002 Code ofPractice for Earth Retaining Structures and BS8004 Code of Practice for Foundations.

.. Reinforcement for soil slopes (cuttingor embankment)

.. Provide a capillary barrier againstrising ground moisture.

In all cases the engineer shall refer to themanufacturers technical literature and checkthe suitability of a geosynthetic for the particularapplication.

There are a number of different trade names ofgeosynthetics available and the usage anddesign of such materiais is dealt with withintheir own respective technical literature.

B5 SAMPLE PRO FORMA FORQUANTIFYING GEOTECHNICALSITE INVESTIGATIONS

The following five pages show a sample proforma Bill of Quantities to be used whenquantifying a site investigation (with notes).The testing programme shown may be reducedor expanding according to the type ofinvestigation required.

It is important to identify each element of workrequired in a schedule in as much detail aspossible. This serves two purposes. Firstly, itacts as a checklist and enables the engineer tolist precisely the requirements of the brief.Secondly, a detailed list with item descriptionsenables the brief to be priced by the tendererson an even basis and reduces the probability ofhidden extra costs.

The pro forma has been split into threesections with notes:

.. Fieidwork

.. Laboratory workIn all cases and for all types of retaining wallsattention should be given to drainage at theback of the wall in order to prevent hydrostaticpressure on the retaining structure and to avoida general rise in pore pressure in the soii orrock mass behind the wall.

January 1997

.. Reporting.

Page B/13

OATAR HIGHWAY DESIGN MANUAL APPENDIX 8

Scope Of Works for Geotechnical Investigation

Project Title

I Project Code

SECTION 1 - FIELDWORK

Ref Item Description Notes Oty Unit Rate(OR)

Total(OR)

F1 Walkover/DeskStudy

Including all permits, and reporting. 1Available data from existing geotechnicalmapping and any other sources shall becombined with a geological walkover surveyof the site. The combined survey shallidentify such areas as rock outcrop,sabkah, water courses, water collectionareas etc. The results are to be marked ontopographical plans of 1:2000 scale or1:500 scale as directed. One copy of theresults are to be submitted to the Engineeras part of the Site Investigation Report(refer R1).

Item

F2 Boreholes

F2.1 Mobilisation All items associated with all mobilisation for 1boreholes including location of boreholes.The approximate location of all boreholes,trial pits and surface samples shall beindicated on the contract drawings. Theprecise positions shall be agreed with theEngineer prior to commencement on site.

Item

F2.2a Drilling of Boreholes Light cable percussion and rotary coredrilling to 20m, including hand dig forservices as required, liaison with utilities,moves between boreholes, photographs,borehole iogs, reinstatement of boreholesand reporting. The Contractor shall providefull information on the strata and theengineering properties of all soils and rockencountered. See Notes 5, 7, 8, 9, 14.

Nr

F2.2b Additional Drilling Addifional drilling depth rate per m below Rate m20m b.g.1.

F2.3 SPT in Borehole In situ SPTs shall be made on allcohesionless and non-cemented strata, inaccordance with QCS Section 3 Part 4 SoilSampling.

Nr

F2.4 Standpipe inBorehole

Installation and monitoring of standpipe inborehole.

Nr

F2.5a Rotary Open .Drilling Rotary open drilling 100mm diameter,including collection and logging of chippingsamples to depths of 30m b.g.l., includingreinstatement.

Nr

F2.5b Additional Drilling Additional rotary open drilling depth, rate Rate mper m below 30m b.g.1.

F2.6 Permeability Test inBorehole

Falling head test to BS 5930. Nr



Ref Item Description Notes Qty Unit Rate Total(QR) (QR)

F3 Trial Pits

F3.1 Mobilisation All items associated with mobilisation for 1 Itemtrial pits.

F3.2a Excavation of Trial Excavation to 1.2m, including liaison with NrPit utilities, moves between trial pits,Hand Excavation photographs, trial pit logs and reporting.

See Notes 6, 7, 8, 9,14.

F3.2b Excavation of Trial Excavation to 3.0m including liaison with NrPit utilities, moves between trial pits,Machine Excavation photographs, trial pit logs and reporting.

See Notes 6, 7, 8, 9,14.

F3.3 Reinstatement of Trial pits shall be backfilled and compacted NrTrial Pit in accordance with QCS. All materials shall

comply with QCS.

F3.4 Soakaway and See Note 17. Nrpermeability Test

F4 Additional Methods

F4.1 Pavement Coring Cores shall not be less than 150 mm Nrdiameter and shall be taken through the fullthickness of the asphalt pavement, suchthat the underlying, unbound material isexposed.All core holes shall be backfilled with fmecold asphalt mixture or similar approved,placed and compacted in layers using asuitable tamper such as a plate attached tovibrating hammer. Backfilling shall takeplace immediately upon completion oftesting.

F4.2 Dynamic Cone DCP testing in accordance with TRL NrPenetrometer Testing Information Note at core locations shall beon Pavements carried out immediately upon completion of

coring and the hole is then sponged dry. Aprofile of the bearing capacity to a depth of800mm below the road surface or untilresistance to penetrate is such that for 30blows less than 5mm of penetration isachieved. The DCP plot and profile shallbe provided at each location. See Note 10.

F4.3 Dynamic Cone DCP testing in unconsolidated material to a NrPenetrometer Testing depth of 2m or until resistance to penetrate

is such that for 30 blows less than 5mmpenetration is achieved. The DCP plot andprofile shall be provided at each location.

F4.4 Plate Bearing Test Test to be carried out at foundation or Nrformation level. Plate to be approximately600mm sq, loading details to be suitable forproject requirements. Contractor to supplyreaction load.

F4.5 Shear Vane Test Test shall be in soft sensitive clays. Vane Nrto consist of four blades 75mm x 150mm.

F4.6 In Situ Density Test Tests shall be by core cutter, sand Nrreplacement or nuclear density metre asappropriate to the soil type.

F4.7 In Situ CBR Tests in accordance with BS 5930. Nr



SECTION 2 • LABORATORY WORK

APPENDIX B

Ref Item Description Notes Qty Unit Rate Total(QR) (QR)

L1 Atterberg Limits See Note 12. Nr

L2 Particle Size See Note 12. NrDistribution

L3 CSR See Note 12. Nr

L4 Chemical Tests pH, Sulphate and Chloride. See Note 12. Nr

L5 Dry Density / Moisture See Note 12. NrContent Relationship

L6 Moisture Content and See Note 12. NrDensity

L7 Triaxial Test See Note 12. Nr

L8 Point Load Test in See Note 12. NrRock

L9 Unconfined See Note 12. NrCompression Test(with Modulus ofDeformation on Rock)

L10 Sedimentation Test See Note 12. Nr

L11 Laboratory See Note 12. NrPermeability Test

L12 Miniature Shear Vane See Note 12. NrTest

SECTION 3 - REPORTING

R1 Site Investigation Comprehensive factual and interpretative 1 ItemReport Geotechnical Report, including

photographs, the number of copies to be asspecified. See Note 13.

NOTES

1 These notes apply to Field Work, Laboratory Work and Reporting. It is assumed that the ratesfor the above items include for the requirements of these notes.

2 The purpose of a geotechnical investigation is to provide information to determine parameterssufficient for concept or detailed design, as required. The investigations should enable theConsultant to advise the Engineer on the requirements necessary for further investigation workthat will enable quantification of the project.

3 All works shall be carried out in accordance with QCS Section 3 Ground Investigation.

4 The Contractor shall exercise the greatest possible care to ensure that both field and laboratorywork are of the highest quality.

5 The measurement of the depth of the trial pits and boreholes shall be taken from the level atwhich the pit or bore enters the ground. The positions of all boreholes and trial pits shall berecorded to within an accuracy of 1m together with the ground levels to the nearest 50mm,related to the Qatar National Datum (refer to QCS Section 3). This-information shall be recordedon the plans and submitted to the Engineer as part of the Report.


QATAR HIGHWAY DESIGN MANUAL APPENDIX 8

6 Trial pits shall be excavated to rock level or otherwise to the limit of the mechanical excavator,nominally a depth of 2.5 m. The depth of boreholes may be varied by the Engineer subject tothe strata encountered on site. Bed rock in boreholes shall be proved for a minimum depth of5m. In cuttings remote from structural foundations, the depth of boreholes shall be 3m belowproposed formation level.

7 All excavations shall be logged by a fully qualified geotechnical engineer or engineeringgeologist and such logs shall form part of the Report. Refer to QCS Section 3 Clause 1.6.7.

8 The equipment used for excavation, boring, sampling and testing shall be subjected to theapproval of the Engineer. Under no circumstances shall water be used to assist boring throughclay.

9 If any object, natural or artificial, obstructs either setting up or progress of excavating and boringthe matter shall be reported to the Engineers Representative, who may direct the excavation orborehole to another location to avoid the obstacle.

10 DCP testing shall be in accordance with the UK Transport Research Laboratory (TRL)Information Note, Operating Instructions for the TRL Dynamic Cone Penetrometer, 1991.

Analysis of the DCP reading shall be made using the latest version of the TRL DCP computerprogramme based on the folloWing relationship between penetration resistance and estimatedin situ CBR:

Log,o (CBR) = 2.48 - 1.057 Log,o (Strength)

It should be noted that this formula may not be applicable to Qatar conditions and resultsobtained should be treated with caution.

The analysis shall account for the effect of water used in the coring process on the aggregatelayers.

11 All rotary core samples shall be retained for a period of six months at the offices of theContractor for the purpose of inspection. All core samples shall be colour photographed andpostcard size prints inserted in each copy of the report. Photographs are to be taken at adistance from core samples to enable a detailed study of the core.

Small disturbed samples shall be taken at changes of strata and at approximately 1.0m intervalswithin each type of material.

Bulk disturbed samples of at least 80 kg weight shall be taken in cohesive materials as directedby the Engineer at a change of strata and not greater than 1.0m intervals within each type ofmaterial. One small disturbed sample shall be taken between each two successive bulkdisturbed samples. The samples shall be sealed, transported, protected and stored such thatno change in moisture content and soil structure occurs.

Surface samples shall be bulk disturbed samples of at least 80 kg weight and these shall betaken in accordance with the recommendations given in BS 5930.

Samples of groundwater of at least one litre shall be taken, and the level at which water is struckand standing water levels shall be observed and recorded

12 All laboratory testing shall be carried out in accordance with the relevant procedures given in BS1377: 1990, Testing of Soils, save that the method for both compaction tests and recompactionof samples of the CBR test, which shall be in accordance with Central Materials Laboratorymethod of test CML 12-97 and CML 10-97.

Soil and groundwater samples shall be analysed for the following:

January 1997

........sulphateschloridespHgrading / classification (as appropriate)

Page 8/17


For each trial pit and borehole, soil samples shall be tested at each change in strata, with aminimum of 2 tests in the overburden above the rock.

Detailed engineering logs shall be submitted, in accordance with QCS Section 3.

13 The Contractor shall submit daily allocation sheets and preliminary iogs and test resuits inaccordance with QCS Section 3 Clauses 1.6.1, 1.4.1 and 1.4.3.

As soon as possible after the completion of the Laboratory Testing, the Contractor shall submit5 copies of his factual and interpretative report, prepared in accordance with QCS Section 3Ciause 1.4.5.

14 The Contractor shall take all reasonable precautions to safeguard all existing on-site services.The Contractor will be held liable for any damage to such services which may be attributable tohis negligence. Refer to QCS Section 3 Clause 1.6.6.

15 The Contractor will be expected to carry out the on-site works expeditiously and in one visit.

16 The Contractor shall give a minimum of 48 hours notice, in writing, to the Engineer, before hecommences any work on site.

The Contractor is to carry out the works to the entire satisfaction of the Engineer, and is to workin such a way that no inconvenience is caused to other contractors, statutory undertakers or thegeneral pUblic who may be in the locality.

The responsibility for obtaining Road Opening Permits and the like shall be upon the Consultant,who shall adhere to all the requirements of any authority.

The Consultant shall allow in his fee submission for all requirements of QCS Section 3 Clause1.6.1 including hand excavation to determine the presence of utility lines prior to thecommencement of mechanical excavation.

17 In selected trial pits, the Consultant shall undertake tests to determine the suitability of thesubstrata to dissipate water. The results of these tests shall be reported and utilised in thedesign of stormwater soakaways, positive drainage systems or water ground relief systems. Thedesign of soakaways shall be in accordance the current CED design practice and BRE Digest365, modified as appropriate for local conditions.

18 The location of utility lines el'lcountered in the excavation shall be logged and their conditionnoted. When trial pits are specified in the Project Brief for utilities location and conditionsurveys, the Consultant shall ensure that a representative of each utility company is present toconfirm the responsibility of the apparatus encountered.


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