Journal - October 2011

7/29/2019 Journal - October 2011

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Printed by Karunaratne & Sons (Pvt) Ltd, Sri Lanka.

Vol. XXXXIV, No. 04, October 2011


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ENGINEERJOURNAL OF THE INSTITUTION OF ENGINEERS, SRI LANKA

EDITORIAL BOARD

Eng. (Prof.) A. K. W. JayawardaneEng. Priyal De SilvaEng. W. T. R. De SilvaEng. (Prof.) K. P. P. Pathirana - Editor TransactionsEng. (Prof.) T. M. Pallewatta - Editor ENGINEEREng. (Dr.) D. A. R. DolageEng. (Miss.) Arundathi WimalasuriyaEng. M. L. Weerasinghe - Editor SLENEng. (Dr.) K. S. WanniarachchiEng. (Prof.) S. S. L. Hettiarachchi

The Institution of Engineers, Sri Lanka120/15, Wijerama Mawatha,

Colombo - 00700Sri Lanka.

Telephone: 94-11-2698426, 2685490, 2699210Fax: 94-11-2699202E-mail: [email protected] (Publications): [email protected]: http://www.iesl.lk

COVER PAGE

Colombo Port Expansion ProjectExpansion of the Colombo port is one of the mega projectsundertaken by the country at an estimated cost of Rs. 36billion, funded by the Sri Lanka Ports Authority (SLPA) &

Asian Development Bank (ADB). The expansion willextend the port towards the sea surrounded by a 6.83 kmlong breakwater. Three terminals each with a length of 1.2km, incorporating three berths apiece are to be formedsurrounding a 18 m deep inner harbour basin of 260 Ha.Including the 20 m deep and 570 m wide access channel,total dredging volume of this landmark project would be15.5 million cum.

Courtesy of:Sri Lanka Ports Authority

CONTENTSVol.: XXXXIV, No. 04, October 2011

ISSN 1800-1122

From the Editor ...

SECTION IDevelopment of Guidelines for Low VolumeConcrete Road Construction in Sri Lankaby : Eng. (Dr.) W. K. Mampearachchi and

Eng. N. A. A. Priyantha

Validity of Reversible Flow Lanes betweenKandy Road Flyover and New Kelani BridgeRoundabout along A01 to accommodate PeakTraffic Flowsby : Eng. (Prof.) K. S. Weerasekera

Effectiveness of Traffic Forecasting onPavement Designs for Sri Lankan Roadsby : Eng. (Dr.) W. K. Mampearachchi and

Eng. P. H. Gunasinghe

SECTION II

Comparison of Rational FormulaAlternatives for Streamflow Generation forSmall Ungauged Catchmentsby : W M D Wijesinghe and

Eng. (Prof.) N. T.S. Wijesekera

Monitoring of Total Suspended Particles &Toxic Gasses in Stationary CombustionSystemsby : Eng. K. T. Jayasinghe

Design of a Wide Input Range DC-DCConverter Suitable for Lead-Acid BatteryCharging

by: Eng. M. W. D. R. Nayanasiri and Eng.(Prof.) J. A. K. S. Jayasinghe, Eng. B. S.Samarasiri

Stormwater Management Modelling for anUngauged Watershed in Matara Municipalityby : Ms.H. M. D. Harshani and

Eng. (Prof.) N. T. S. Wijesekera

The statements made or opinions expressed in the

Engineer do not necessarily reflect the views of theCouncil or a Committee of the Institution ofEngineers Sri Lanka, unless expressly stated.

Notes:

ENGINEER, established in 1973, is a QuarterlyJournal, published in the months of January,April, July & October of the year.

All published articles have been refereed inanonymity by at least two subject specialists.

Section Icontains articles based on EngineeringResearch while Section II contains articles ofProfessional Interest.

1

11

17

29

37

47

55

III


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FROM THE EDITOR..

Colombo, before becoming the capital and then the financial capital of Sri Lanka wwell known throughout most part of our long history as a port, Kolomthota. Natursetting and geographical considerations would have prompted our ancestors in selectinthis location for the said purpose. Today, Colombo is an internationally known anhighly trafficked port, strategically located in close proximity to major economic sroutes.

Development and expansion of the Colombo port therefore would be an imperative fthe future economic development of Sri Lanka, if no other port of that statureavailable to the country. With the commissioning of the vast Hambanthota port, whicis situated even more closely to international sea routes, it may seem superfluous

expand Colombo port at such a trouble and cost. However, as timing is of essence in teconomic race, making Colombo port with expansions fully functional, targeted fcompletion in April 2012 could be the expeditious path to follow.

Eng. (Prof.) T. M. Pallewatta, Int. PEng (SL), C. Eng, FIE(SL), FIAE(SL)

Editor, ENGINEER, Journal of The Institution of Engineers.


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section i


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1ENGINEER

Development of Guidelines for Low Volume ConcreteRoad Construction in Sri Lanka

W. K. Mampearachchi and N. A. A. Priyantha

Abstract: The purpose of the study was to develop guidelines for construction of low volumeconcrete roads in Sri Lanka. A survey was carried out to study current concrete road constructionpractices and knowledge of the contractors involved in concrete road construction. Survey resultsshow that good practices have not been adopted in low volume road construction in Sri Lanka. Theauthors have introduced best practices which can be easily adopted by the local road constructionindustry.Incorrect joints construction was observed in concrete roads during the site visit and the Authors have

introduced a new device for contraction joint construction. A modification to the available method

was proposed to measure surface undulation on local concrete pavements and allowable undulation

was determined through field investigation. A comparison of various kinds of concrete producing and

curing methods and their performance were studied. The authors have evaluated the effectiveness ofrebound hammer method which has been used for quality control by some consultants. Rebound

hammer reading was compared with compressive strength which was found out from core cutter

samples. Double beam vibrator with inbuilt camber was introduced to consolidate and form the

camber of the surface layer.

Check lists for subgrade /subbase, shoulder, formwork and concrete placing and finishing have been

introduced to address weakness and enhance the quality of the pavement construction. Quality and

Cost control techniques in the field of low volume concrete road construction in Sri Lanka are also

described. Further, the proposed guideline describes the most appropriate methods for preparation of

subgrade, subbase and shoulder, and mixing, placing and finishing of concrete.

1. Introduction

Concrete has been used for road construction

at special locations in the past in Sri Lanka.

One of the oldest roads is Chaitya road

(marine drive) at Colombo port which used

pre tensioned, post tensioned and

conventional concrete [5]. Concrete paving has

been widely used for low volume roads in SriLanka since 2007 as the government allocated

funding for local government agencies to

construct concrete roads. Low volume roads

are normally considered as roads with

relatively low traffic volume, an Average Daily

Traffic (ADT) of less than 400 vehicles per day.

These roads are the tertiary links to the road

network and provide access to land and

properties

Concrete surfacing is considered as a cost

effective road construction technique for low

volume roads since concrete roads have less

maintenance cost. Currently, few roads

managed by the Road Development Authority

(RDA), have been constructed using concrete.

2. Cost Effectiveness of Concrete

RoadsPast research and findings reveal that concrete

has added advantages than the asphaltpavements. Some of the early findings have

shown that concrete has been a cost effective

solution.Life Cycle Cost Analysis (LCCA) is a forward-

looking decision framework that helps assess

Eng (Dr.) W. K. Mampearachchi, B.Sc. Eng. (Hons)(Moratuwa), MSCE(south Florida), PhD(Florida), CMILT(UK)., MIE(Sri Lanka), Senior Lecturer, Department ofCivil Engineering, University of Moratuwa, Sri Lanka.Eng. N. A. A. Priyantha, B.Sc Eng. (Moratuwa),M.Eng(Highway and Traffic, Moratuwa), MIE(Sri Lanka),Site Engineer, Kumagai Gumi Company, STDP.

enGineeR - Vl. XXXXiV, n. 04, pp, [1-9], 2011 th iu f egr, sr Laka


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ENGINEER 2

the lifetime costs of a roadway, rather than

merely considering the initial construction

costs. When LCCA is applied, concrete

pavement is, in many cases, less expensive

than an asphalt surface of equivalent design

[1].Concrete highways have an excellent track

record as a cost-effective investment in theUnited States. Rigid concrete pavement

outperforms flexible asphalt pavement impact

on the environment. Nearly 30 percent of U.S.

interstate highways are built with concrete

[11].

Data from the American Concrete Pavement

Association confirms that American states are

truly committed to building concrete highways

and create competition between the concrete

and asphalt paving industries resulting in

lower unit costs for both concrete and asphalt

highways [8]. This results in more roads being

paved for the same cost.

Extensive studies by the National Research

Council of Canada[12] confirm previous

findings of fuel efficiency of vehicles on

concrete roads [13] showing that fully loaded

tractor-trailers consume less fuel traveling on

concrete pavements than on asphaltpavements over a wide temperature range.

3. Problem StatementICTAD Standard Specifications for

Construction and Maintenance of Roads and

Bridges Sri Lanka [9, 10] specify some

guidelines for concrete road construction.

However, most of the details in the

specification are related to concrete pavements

which are supposed to be constructed usingpavers. Still, we have not used pavers for

concrete road construction in Sri Lanka and it

would not be feasible for low volume roads

due to poor road alignments. In the literature

review, the Authors have not found any

guidelines for low volume concrete road

construction.

We have identified the following major issues

in the questionnaire survey. Neither pavement

thickness nor compressive strength ismeasured before payments are released to

contractors. One of the qualitative parameters

of a concrete pavement is roughness.

Roughness or surface undulations are

measured by standard straight edge and it

should be modified to measure surface

undulation of local concrete roads. Full depth

joints have been seen in local roads and no

load transfer between panels. Ineffectivecuring methods have been used for curing

concrete. Concrete transit trucks have been

used for concrete mixing. Concrete has not

been compacted in certain projects.

The study is focused on development of

guidelines for construction of shoulders,

subbase, formwork and concrete surfacing

based on the condition survey on newly

constructed low volume roads in the rural

sector.

4. Concrete Road Condition

SurveyDistressed locations and wrong construction

practices have been observed during the site

visits.. A survey was done on 24 roads which

are located in the Southern Province, to collect

concrete road condition data (post

construction) and the Authors met the

contractors and stakeholders of the surveyed

roads to gather their knowledge and

experience on concrete road construction. The

Authors made a few site visits to concrete road

construction sites to observe construction

practices.

According to the survey, contraction joint

spacing is less than 5m in 45% of the roads and

these joints are not straight in 41% of the roads.

Wooden planks have been used to provide

contraction joint in 45% of the roads and these

have not been removed in 98% of such roads.According to the survey results, no camber has

been provided in 92% of the roads. Curing

had been done on 70% of the roads while

curing material had been provided for only 4%

of the roads. According to the specifications,

instructions had been given to provide a

separation membrane between the concrete

layer and the sub-base layer, but according to

the survey, polythene sheets had been used as

a separation membrane only in 25% of theroads.


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5. Pavement Strength and

Thickness

Three concrete core samples were taken from

roads as shown in Table 01, using a core cutter

machine, and the specified mix proportion of

the concrete was 1:2:4 (cement : sand :

aggregate) . Thickness and strength of the

samples are shown in Table 01. Design

strength of 1:2:4 concrete is 15N/mm2 and

according to Table 01 specified design strength

was achieved only at Wadihitiniwasa road.

Specified pavement thickness was 150 mm and

that has not been maintained even in a single

case.

Core samples were tested from sites where

concrete mixing had been done by concretetransit trucks. It has been observed, during site

visits that the concrete discharged from transit

trucks was not properly mixed as transit trucks

are designed for concrete transportation only.

Arrangement of blades inside the rotating

drum of a concrete transit truck and a concrete

mixer was studied. Visual observations have

also proved that concrete transit trucks are not

suitable for mixing concrete. Furthermore,

rebound hammer tests were also carried out on

some roads. In addition to that, a few rebound

hammer tests were carried out on concrete

roads which have been constructed using

concrete mixers. Standard deviation of

pavement strength was calculated in both

cases and a comparatively high standard

deviation on roads constructed by using

concrete transit was not trucks. All these facts

prove that concrete transit trucks are not

suitable for mixing concrete.

The paving thickness was less than thatspecified. The core sample which satisfied the

strength requirement has the lowest thickness.

It was found that the payment was released

based on the hammer reading and the strength

was compensated by the thickness to get

approval from the authorities.

Table 1 - Core sample strength.

No Location Thickness

Strength

N/mm2

01Beligaswatta

Kohilawala Para140mm 9.96

02Wadihitiniwasa

Para, Beliatta95mm 16.45

03Dewana Piwisum

Para, Ihalabeligalla140mm 10.76

Figure 1- Concrete core samples

Rebound hammer can be used to measure

surface hardness of concrete pavements where

surface hardness correlates with strength of

the pavement. However, surface hardness

depends on various factors such as moisture

condition of surface, aggregate size etc (BS

4408:PART 4) [6] It is advisable to use hammer

test as a field test for quality control since it is

possible to test the overall pavement.

However, core sample testing should be

conducted for quality assurance to verify the

hammer results (strength) and the pavement

thickness.

6. Effectiveness of Curing

Material

Low rich concrete is being used for local road

concrete pavements and according to Sammir

et..al, curing should be done for at least 7 days

for such concrete.[7]

Saw dust was used as water retaining material

at Napekanda road while coir dust was used atBeligaswatta road since these materials were


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ENGINEER 4

freely available. Sandy soil can also be used as

a water retaining material.

Effectiveness of curing depends on water

retaining ability of such materials, and in order

to compare the effectiveness of different

materials, an experiment was conducted on a

dry sunny day (maximum temp of 35C). Onemeter by one meter rectangles were marked on

the selected pavement.. After that 27000cm3 of

measured coir dust was spread evenly on the

first block and the same volume of sandy soil

was spread on the second block while keeping

the third block as a control surface. Water was

spread on the coir dust, sandy soil and control

section to saturated conditions at 6:30 am.

Intervals at which water was spread on the

control section (without a curing material) tokeep it in a wet condition are given in Table 2.

It was found that coir dust and sandy soil

sections remained in a wet condition during

the study period. Results show that water

spraying is required in 1 hour intervals in

morning and evenings and in 30 minute

intervals during mid day for curing concrete

without a water retaining material. It can be

concluded that it is essential to use a water

retaining material for effective curing of road

sections.

Table 2- Water retaining material testing

data.

Time

Time

deference

(Minutes)

Slab

without

material

Coir

dust

Sandy

soil

6:30 7:30 60

8:50 80 9:55 65

10:45 50 11:20 35 11:55 35

12:50 55 13:42 52 14:33 51 15:30 57 16:30 60

Note: - () Water spread () water not spread

7. Measuring Surface Undulation

With reference to the available specification,

surface undulation of a concrete pavement

shall be evaluated by a standard 3 m straight

edge, but if there is a camber, this length

cannot be used to measure undulations ofconcrete roads, because the average width of

local roads is about 3 m. In this case, the

standard straight edge was modified to

evaluate undulations in low volume concrete

pavements in Sri Lanka.

An aluminum rectangular hollow box of 1.5 m

length, 50 mm height and 25mm width was

used as the modified straight edge. The length

of the selected straight edge was 1.5 m since

half width of most concrete roads is about 1.5m. Two supports of height 20 mm were fixed

at the ends of the straight edge. A wedge

which is used to measure the space between

the concrete surface and straight edge was

prepared from a steel plate with a handle. The

length of the wedge was 350 mm and height 50

mm as shown in figure 02.

Surface undulations were measured in selected

roads in the Galle district after the field survey.

Table 3 shows the data collected from

Kahaduwa Milidduwa road in Galle. This road

has been rated as a good surfaced road in the

survey. It can be seen that undulations

exceeded 10 mm only at three locations. This

study shows that 10 mm of undulation can be

allowed for rural road construction and it can

be achieved with available resources.

Figure 2 - Modified straight edge


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8. Construction of Joints

Shrinkage stresses are induced in concrete

pavement with the hydration of cement and

shrinkage continues for a long period. As a

result of these stresses irregular cracks can be

induced in concrete. These cracks can beavoided by providing partial depth joints at 4-

5 m intervals so that cracks due to stress are

developed under the formed joint. The joint

requires only a saw cut upto 1/3 of the

pavement thickness. All the joints observed

during the survey were full depth joints

(wooden plank placed to separate slabs). Full

depth contraction joints are weak in load

transfer between slabs and an experiment was

carried out to construct half depth contraction

joints at Napekanda road by adopting special

procedures.

The location for a contraction joint was

identified and a 14 mm wide groove was

prepared on both sides of the formwork upto

half of its depth as shown in figure 03.

Thereafter, the plywood was covered with a

polythene sheet, as shown, and was inserted

into the groove. The objective of covering the

plywood with a polythene sheet was to

prevent concrete sticking to the plywood.Concrete was then poured into both sides of

the joint. The plywood plank was then

removed, slowly, about 4 hours after pouring

of concrete leaving the polythene sheet with

the concrete. This joint construction method

has been further developed by limiting the

joint width to 6mm using a perspex sheet

instead of the plywood plank. Mould oil can

be used instead of a polythene sheet to prevent

sticking of concrete to the Perspex sheet.Figure 4 shows the contraction joint

construction mechanism developed by the

University of Moratuwa.

Table 3 - Reading of surface undulations

Chainage

Max.

LHS

Reading

(mm),

A

Undulation

(mm)[A-20]

Max.

RHS

Reading

(mm),A

Undulation

(mm),[A-20]

+000 22 2 25 5

+020 27 7 25 5

+040 30 10 30 10

+060 40 20 15 -5

+080 30 10 20 0

+100 20 0 22 2

+120 20 0 26 6

+140 27 7 32 12

+160 28 8 33 13

+180 30 10 24 4

Average 7.4 5.2

SD 5.37 5.2

Figure 3 -Construction of half depth

contraction joint

Figure 4 -Contraction joint making device

developed by University of Moratuwa

Furthermore, a few half depth contraction

joints were constructed at AduranwilaEhalagedara Para, Poddala, Galle by the

Authors. The construction process of the half

depth joints was different from that of

Napekanda because a Styrofoam sheet of

50mm width was used while total thickness of

the pavement was 100mm. The Styrofoam

sheet was removed on the day following

concreting..

If concrete paving is done without providing

joints, cracks will form naturally [3] and thiswas observed during the condition survey.

Also. it was found that natural cracks had

Polythene sheet

14mm widegroveinformwork

6mm Perspex stripfixed between twowoodenstrips

Formwork


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ENGINEER 6

developed on 7 roads out of 24 which have not

been provided with contraction joints. The

average spacing of these natural cracks was 12

m.

9. Camber / Transverse Slope.

According to Vazirani et..al[14], camber for

concrete pavements should be kept between

1.7% and 2%. According to guidelines

provided to contractors, requirement of a

camber or transverse slope has not been

mentioned. As a result, camber was not

provided on 92% of the concrete roads.

Construction of camber is not difficult and 2%

camber was achieved at Napekanda road

without much effort. It is essential to have a

camber in the road surface for surface water

runoff and also for each layer below (drain out

infiltrated water to side drains) and should be

included in the guidelines.

10. Compaction of Concrete

It was found, in the survey, that concrete was

not compacted using a vibrator when placed. It

is not advisable to use a poker vibrator for

compaction of thin concrete layers. TheAuthors have developed a double beam

surface vibrator with an inbuilt camber (2%) to

compact thin concrete layers used in low

volume road construction. Vibration was

created by placing a 1 hp motor with an

eccentric weight at the center. Figure 5 shows

the double beam vibrator for compaction of

concrete. It is made of hollow aluminum

sections with a steel channel for the camber.

Two handles located at the ends can be used tomove the vibrator forward over the formwork.

Forward speed is critical in the correct use of

the vibrating beam and should be limited to

between 0.5 and 1.0 m/min. The lower speed

should be used for thicker slabs. A second pass

at a faster speed may be made for better

finishing.

Figure 5 -Double beam surface vibrators

11. Other Considerations

The recommended slump for concrete

pavements, in India, is 25mm to 50mm, if

paving is done by pavers [14]. The slump was

measured during construction of Aduranwila

Ehalagedara road and it was between 75mmand 125mm. Literature shows that a slump of

50- 100 mm is sufficient for placing concrete.

However, excessive slump should not be

allowed since it will lead to using more free

water for concrete preparation. Close

supervision is required at the paving site to

ensure quality of concrete.

Permanent marks on the pavements were

observed on 50% of roads due to their

premature use. Access to pedestrians, vehicles

or animals should not be allowed before

concrete has gained sufficient strength in order

to avoid permanent marks. Barricades are

suggested as a solution for this purpose.

During the site visit at Agunukolapalassa,

structural damage of the pavement was

observed due to heavy vehicle movements

before gaining sufficient strength and these

damages are more critical than permanent

marks.

Motor witheccentric load

Handle

Formwork

2%Camber


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The shoulder provides space for pedestrians

and additional space for traffic. Shoulders can

be constructed either before or after placing

concrete. Construction of shoulder before

placing concrete is the better practice. Shoulder

construction should be delayed until the

concrete gains sufficient strength in the eventof construction of the shoulder after placing

concrete.

Side drains for disposal of storm water should

be constructed and maintained to increase the

lifespan of the pavement. It was observed that

proper drainage has not been constructed in

the roads selected for the survey.

12. Conclusions and

Recommendations

Design weaknesses and poor construction

practices were observed during the condition

survey. Summary of good practices to

overcome design and construction weaknesses

are given below.

1. One third to half depth contractionjoint should be provided at 4-5m

intervals using 6 mm to 12 mm wide

plywood planks. A device developed

by the University of Moratuwa with a

6mm perspex sheet is recommended to

make the contraction joints.

2. According to the survey, concrete wascured on 70% of the roads and

effectiveness of curing can be

enhanced with coir dust, saw dust or

sandy soil as water retaining material.

3. The use of concrete transit truckswhich are designed for transporting

concrete, for mixing of concrete shouldbe discouraged. As a result of poor

mixing of concrete, in transit trucks,

concrete strength is lowered and leads

to a low quality product.

4. Roughness or surface undulationaffects travel comfort of vehicle

occupants. A straight edge of 1.5m

long, is specified for controlling

undulations of concrete surface and

test results show that undulations of

10mm or less for 1.5m straight edge

provide a good surface for low volume

concrete roads.

5. Compaction of concrete using surfacevibrators has not been done in low

volume concrete road construction. It

is recommended to use double beam

vibrators developed by the University

of Moratuwa to consolidate and formthe surface cross fall of concrete roads.

6. Load bearing capacity of a concretepavement is related to its thickness

and compressive strength. Thickness

of the pavement after construction is

not easily obtained and core cutter

should be used to extract samples.

Extracted samples can be used to

measure concrete thickness and test

for compressive strength. Compressive

strength and the thickness of the

random samples should be evaluated

before releasing payments to the

contractor.

Weaknesses in current construction practices

were identified during site visits and through

interviews with personnel involved in

construction, maintenance and administration

of concrete roads. Check lists were developed

to include the good practices and to enhancequality of low volume concrete roads as given

in the Appendix. Contractors should use the

check list, and work under each item should be

certified by the consultant or the project

management unit of the project before moving

to the next item.

References

1.

American Concrete Pavement Association,Life Cycle Cost Analysis: A Guide forComparing Alternate Pavement Analysis, EB2002, 220P.

2. Design and Construction of Joints forConcrete Streets, Concrete Information,

American Concrete Pavement Association,

IS061.01P.(ACPA 1992), 1992.

3. Guruchandran, Singh & Jagdish Singh,Highway Engineering, Standard Publication

Distributors Delhi, Fifth Edition, 2008.


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ENGINEER 8

4. Kadyali, L. R., & Lal, N. B., Principles andPractice of Highway Engineering, Khanna

Publishers, Delhi -6 fifth edition, 2008.

5. Kulasinghe, A.N.S., Construction ofMarine Drive in Colombo including Sea

Walls, New Lighthouse and Concrete

Roadway in Prestressed concrete.1951,

http://kulasinghe.com/shells.htm

6. WSDOT, Rebound Hammer Determinationof Compressive Strength of Herded

Concrete, WSDOT Material Manual, M46-

01.03, January 2009.

7. Samir, H, AL Ani and Mokdad, A. K. ALZaiwary(1988) The Effect of Curing Periodand Curing Delays on Concrete inHhotWeather, Building Material Development,

Building Research Center Bagdad, Iraq2005-212.

8. Southeast Chapter American ConcretePavement Association, Whosays...Concrete Pavement Costs Too Much?Count on Concrete Pavement, 2005.

9. Standard Specifications for Constructionand Maintenance of Roads and Bridges,

Institute for Construction Training and

Development, Sri Lanka, Revised Draft

Document 2005.(SSCM 2005).

10. Southern Transport Development Project,Highway Section Kurudugahahetekma to

Matara. Volume 3-Technical specification

2001(STDP 2001)

11. US Department of Transportation FederalHighways Administration web site, Officeof Highway Policy Information, HighwayStatistics 2005.http://www.fhwa.dot.gov/policy/ohim/hs05/xls/hm12.xls

12. Taylor, G.W., Patten, J.D., Effects ofPavement Structure on Vehicle FuelConsumption Phase III, prepared forNatural Resources Canada Action Plan

2000 on Climate Change and CementAssociation of Canada, January 2006.

13. Taylor, G.W., Dr. Farrell, P., and WoodsideA., Additional Analysis of the Effect ofPavement Structure on Truck FuelConsumption, prepared for Government ofCanada Action Plan 2000 on Climate

Change, Concrete Roads AdvisoryCommittee, August 2002.

14. Vazirani, V. N., & Chandola, S. P., Concisehandbook of Civil Engineering, S Chand andCompany LTD, New Delhi, revised edition2008.


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AppendixRoad name:- Chainage:-Checked By:- Designation:-Date:- (All items to be checked in 'Done' column. NA if not applicable)

A. Check List for Sub Base/ ShouldersNo Description Done

1 Is available soil, Granular material, borrow material approved

2 Is material free from debris or any other ingredient that may deteriorate

3 Is the sub base on stable firm ground?

4 Is borrow material from approved borrow areas ?

5 Is plant adequate for on site operations

6 Is the area of work set out?

7 Is previous layer approved?

8 Is each layer parallel to the final sub base layer

9 Is compaction plant approved

10 Has a compaction trial been undertaken

B.Check List for Form WorkNo Description Done

Is vertical alignment as specified?

Is horizontal alignment as specified?

Are dimensions as per specification?

Are Supports as per requirement?

Are Quality and thickness of shutters as per specification?

Are Quality and location of supports as per requirement?

C. Check List for Concrete Placing

No Description Done1

Beforeconcreting

Has the method of construction been approved2 Is formwork alignment, dimensions, rigidness & surface cleanliness

sufficient?3 Are Joints between formwork closed (no gaps) ?4 Are extraneous material removed from the forms immediately before

placing concrete?5 Are Forms treated with approved oil?6 Is sub base surface with the required moisture content?7 Is the sub base surface undulation at approved level?8 Mixing and compaction machines as required and in good condition?9 Are sand, metal and cement at required specification?10 Is material measuring method at acceptable level?

11 Is concrete hauling method at acceptable level?12 Are surface leveling tool and booming tool available?13 Are covering sheets available if it rains?14 Is slump cone and test mould available?15

Duringconcreting

Is concrete placed without segregation?16 Is concrete compacted well?17 Are the final surface level, thickness and undulation at acceptable

levels?18

Afterconcreting

Does the road close for traffic satisfactorily ?19 Is Water retaining material (core dust) available at site ?20 Is concrete being curing satisfactorily for minimum of 7 days?

Remarks

..

Date Signature


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18/71

11ENGINEER

Validity of Reversible Flow Lanes between KandyRoad Flyover and New Kelani Bridge Roundabout

along A01 to Accommodate Peak Traffic Flows

K. S. Weerasekera

Abstract: This paper examines ways of enhancing road capacity by improving lane efficiencyalong Colombo-Kandy Road (A01) at Colombo city entrance by introducing reversible traffic flowlanes between Kandy road flyover at Pattiya junction and New Kelani Bridge roundabout, to cater forpeak traffic flows. A traffic study was conducted between Pattiya junction and New Kelani Bridgeroundabout to find out the benefits and any losses, if reversible traffic flow lanes are introduced alongthis stretch of road during peak traffic flows in mornings and evenings. Two options of laneassignment were considered for the heavy flow direction during peak hours. Option ( i ) by addingone extra mixed traffic lane towards the heavy flow direction while reducing a lane from the oppositedirection, and option ( ii ) adding an additional lane exclusively for buses towards the heavy flowdirection while reducing a lane in the opposite direction. These two options were considered for bothmorning and evening peak traffic flows. By using Davidsons model the benefits or any losses intravel time was computed for the two options separately for both directional peak traffic flows.

The study proved that by the introduction of reversible flow lanes along the considered section,during morning and evening peak traffic flows, the benefits obtained by far outweigh the losses dueto minor reduction in road capacity in the opposite directional traffic flows. It was also found thatintroduction of designated lanes for buses only further improves the overall efficiency of the systemwith higher benefits. If buses only lanes are introduced it is of the utmost importance to implementthese lanes only for buses, as expected.

Keywords: Reversible Flow Lanes, Contra Flow, Tidal Flow, Bus Lanes

1. Introduction

Colombo Kandy road (A01), is one of themain arterial roads of Sri Lanka radiating fromColombo, which carries traffic travellingtowards the central hills as well as northern andnorth central areas of the country. Hence, this isone of the busiest roads in Sri Lanka whichlinks Colombo with other major areas of theisland. The inbound traffic towards Colombo isvery heavy during the morning peak hours

near the city entry, and severe congestion oftraffic is experienced during the week days(Figure 1). Similar conditions are observedduring evening peak hours on weekdays in theoutbound direction. This traffic congestioncosts the state dearly by means of increasedtravel time, fuel wastage, vehicle wear and tear,loss of safety, pollution of air and noise etc.

Figure 1 Inbound Traffic towards Colombo

A newly built flyover above the main railwayline at Pattiya junction is of four lanes with twolanes in either direction (Figure 2). The distancefrom the flyover to the New Kelani Bridgeroundabout is 2 km. This stretch of 2 km roadconsists of six lanes in an undivided

Eng. (Prof.) K. S. Weerasekera, BSc Eng (Moratuwa),MEngSc (UNSW), PhD (UNSW), FIE (Sri Lanka), CEng,IntPE(SL), MIE (Aust), CPEng, MIHT (UK), MASCE,Professor in Civil Engineering, Department of CivilEngineering, The Open University of Sri Lanka.



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ENGINEER 12

carriageway with 3 lanes in either direction.With the introduction of the new flyover atPattiya junction the interruption to A01 trafficarising from frequent rail gate closures of themain railway line has been eliminated, but thecongestion between Pattiya junction and theNew Kelani Bridge roundabout has not

reduced.

Figure 2 Pattiya Junction Flyover along A01

It is observed that during peak flows, the traffictowards the heavy direction is extremely heavy,but in the opposite direction the road space isnot utilised effectively (see Figure 1). Hence,this study intends to investigate the benefitsthat could be reaped by introducing reversible or

contra flow traffic flow lanes.

2. Reversible Traffic Flow Lanesor Contra Flow Lanes

In busy arterial roads, when the movement oftraffic is very heavy in one direction during acertain period of the day, and also becomesvery heavy in the opposite direction duringanother time of the day, this phenomenon iscommonly termed as tidal flow. As a solutionto address the tidal flows reversible lanes can

be introduced. A reversible lane is one, wherethe direction of traffic movement is changedaccording to the intensity of traffic flow in aparticular direction (Kadiyali [1]; Salter &Hounsell [2]).

3. Traffic Data Collection

A manual classified traffic count wasperformed for 16 hours at a location at 1 kmsouth of Pattiya junction flyover (i.e. towardsColombo) on a normal working day from6:00AM to 10:00PM. Two-directional traffic wasrecorded separately at 15 minute intervals at

the counting location for 7 different categoriesof vehicles.

The seven broad categories of vehicles were;three-wheelers, cars & SUVs, all vans, all typesof buses, goods carrying vehicles, all vehicleswith 3 axles, and vehicle with 4 axles or more as

indicated in Tables 1 & 2. The Passenger CarUnit (PCU) factors based on RDA records, forthese separate categories of vehicles on flat terrain

roads with multiple lanes are indicated in Table3.

Table 1 Hourly Traffic Volume(To Colombo) at Peliyagoda on A01

Time TWL CAR VAN BUS GV 3A 4 Total

6 - 7 284 946 423 414 129 17 6 2218

7 - 8 644 1481 399 352 167 2 8 3052

8 - 9 503 1076 195 217 220 7 7 2224

9 - 10 411 863 162 184 245 2 21 1890

10- 11 333 694 146 155 219 14 10 1572

11- 12 502 468 189 197 195 11 28 1589

12- 13 421 541 230 233 169 13 31 1639

13- 14 428 407 233 210 176 22 20 1495

14- 15 321 562 175 197 160 10 17 1441

15- 16 354 571 170 225 163 12 20 1515

16- 17 294 504 226 209 188 18 14 1453

17- 18 224 485 266 256 97 14 21 1363

18- 19 305 484 204 309 118 13 26 1459

19- 20 303 478 161 225 101 17 17 130120- 21 165 311 166 186 91 24 15 958

21- 22 135 265 149 148 66 15 9 788

6 - 22 5627 10136 3493 3717 2504 211 267 25955

Table 2 Hourly Traffic Volume(To Kandy) at Peliyagoda on A01

Time TWL CAR VAN BUS GV 3AV 4A Total

6 - 7 118 196 112 189 90 2 3 710

7 - 8 304 328 152 216 100 21 25 1146

8 - 9 251 309 114 226 171 3 10 1084

9 - 10 250 287 119 188 234 17 20 1114

10- 11 330 400 173 184 295 14 18 1414

11- 12 337 402 175 237 307 11 15 1484

12- 13 327 352 169 267 272 11 21 1419

13- 14 367 423 264 270 286 7 24 1641

14- 15 234 439 349 284 245 13 19 1584

15- 16 380 450 216 230 310 12 22 1620

16- 17 245 517 240 282 343 20 20 1668

17- 18 250 928 311 290 254 12 23 2068

18- 19 403 1024 323 300 211 21 14 2296

19- 20 433 1252 377 340 210 22 19 2653

20- 21 334 649 242 260 209 19 29 1741

21- 22 279 515 210 220 156 12 26 1419

6- 22 4841 8471 3548 3983 3694 217 308 25061


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13ENGINEER

Table 3 Equivalent Passenger Car Units(PCU) for Flat Terrain Multiple LaneRoads

TWL CAR VAN BUS GV 3A 4A

0.8 1.0 1.5 2.0 1.7 2.8 3.5

A separate short duration vehicle occupancycount was conducted during peak hours toobserve the average number of passengerscarried by different categories of vehicles.

Peak hour average passenger count indicatedthat, the average occupancy of a bus is around40 passengers and all other vehicles consideredas a mix is around 3.25 passengers per vehicle.These values were used for computing vehicleoccupancy in the study.

Figure 3 shows two-directional hourly trafficflows separately, and also the total hourlytraffic flow along the considered road sectionover the counting period from 6:00AM to10:00PM.

Traffic Flow on A1 at Peliyagoda

0

500

1000

1500

2000

2500

3000

3500

4000

4500

6:00-7:00

7:00-8:00

8:00-9:00

9:00-10:00

10:00-11:00

11:00-12:00

12:00-13:00

13:00-14:00

14:00-15:00

15:00-16:00

16:00-17:00

17:00-18:00

18:00-19:00

19:00-20:00

20:00-21:00

21:00-22:00

Time (hours)

Traffic

Flow

(veh/hr)

To Colombo

From Colombo

Total

Figure 3 Hourly Traffic Flows on A01 atPeliyagoda

4. Methodology & Analysis

From the traffic survey results it was identifiedthat the morning peak is from 7:00AM to8:00AM and the total vehicle volume towardsColombo is around 3050 vph. During themorning peak the total vehicle volumetravelling out of Colombo was around 1150 vph(see Figure 3). The total two directional flowwas around 4200 vph.

Similarly, the out-bound traffic reaches its peakin the evening between 7:00PM to 8:00PM andthe volume is around 2650 vph. During the

evening peak the total vehicle volume towardsColombo is around 1300 vph (see Figure 3). Thetotal two directional flow was around 3950 vph,

which was less than the morning peak flow.This can clearly be seen in Figure 3.

There are several models available to computethe travel time [3].

(i) The Bureau of Public Roads (BRP) model

used in the UK, (ii) Greenshields model, and(iii) Davidsons model are few models thatcould be used in computing the travel timebenefits or losses.

It was decided to use Davidsons model [4], tocompute the travel time benefits or losses sinceit suited better with local parameters and forbetter relative accuracy. Davidsons modelconsiders parameters such as type of road, roadwidth, frequency of signals, pedestriancrossings, and parked vehicles etc.

Davidson [4] successfully used the followingmodel to compute travel time differences forvarying lane options for urban arterial roads aswell as freeways.

)1(

)1(10

y

yjtt

Where,

t - travel timeat traffic flow q

0t - time taken to travel with no other traffic

(i.e., zero flow travel time)

q traffic flow (veh/hr/lane)

s - saturation flow (veh/hr/lane)

y = q/s

j - level of service parameter

j is theLevel of Service (LOS) parameter whichis related to the type of road, road width,frequency of signals, pedestrian crossings, andparked vehicles. Blunden and Black [5] suggest

following values forj.

j = 0 to 0.2 for freewaysj = 0.4 to 0.6 for urban arterialsj = 1 to 1.5 for collector roads

Hence it is reasonable to assume j = 0.5 forColombo Kandy road.


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ENGINEER 14

Zero flow travel time (0

t ) was taken as 2

minutes assuming a desired speed of 60 km/hover the study distance of 2 km with no othertraffic.

This study intends to consider several optionsof lane operations between Pattiya junction andNew Kelani Bridge roundabout. This roadstretch of 2 km in length (Figure 4) consists of 3lanes in each direction.

Figure 4 Site Layout

Morning Peak Flows:

Option ( 1 ) During the morning peak, to have4 lanes (with mixed traffic) operating towardsColombo bound direction, and 2 lanes (withmixed traffic) operating for out of Colombotraffic as shown in Figure 5.

Figure 5 Lane Operation Option ( 1 )

Option ( 2 ) - During the morning peak, tohave 3 lanes (with mixed traffic) and anotherlane exclusively for buses operating towardsColombo inbound direction, and 2 lanes (withmixed traffic) operating for out of Colombotraffic as shown in Figure 6.


Evening Peak Flows:

Option ( 3 ) During the evening peak, to have4 lanes (with mixed traffic) operating towards

out of Colombo direction, and 2 lanes (mixedtraffic) operating towards Colombo as shown inFigure 7.


Option ( 4 ) - During the evening peak, to have3 lanes (with mixed traffic) and another laneexclusively for buses for traffic going out ofColombo, and 2 lanes (with mixed traffic) forColombo bound traffic as shown in Figure 8.


Davidsons model was applied to compute thebenefits or losses of saving on travel time, and

then the best options were selected.Computation is summarised in Tables 4 & 5respectively for morning and evening peakflows.

Bus

Bus

Kandy

Colombo

Kandy

Colombo

Kandy

Colombo

Kandy

Colombo

Flyover

Roundabout

To Negambo ToKandy


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15ENGINEER

Table 4 Application of Davidsons Model for Two Directional Traffic in the Morning PeakTo Colombo Direction (PHF 7:00AM to 8:00AM) --------->

Existing Option ( 1 ) Option ( 2 )

Mixed Mixed Mixed Mixed Bus Mixed Mixed----> ----> ---->

---->

vph 3050 1150 3050 1150 350 2700 1150

(Bus/hr) 350 220 350 220 350 - 220pcu 3615 1550 3615 1550 700 2910 1550

Lanes 3 3 4 2 1 3 2q 1205 517 904 775 700 970 775

s 2000 2000 2000 2000 2000 2000 2000

y = q / s 0.603 0.259 0.452 0.388 0.350 0.485 0.388j 0.5 0.5 0.5 0.5 0.5 0.5 0.5

T 2 2 2 2 2 2 2

t = travel time 3.516 2.349 2.825 2.633 2.538 2.942 2.633Occupancy - M 3.25 3.25 3.25 3.25 50 3.25 3.25

Occupancy - B 50 50 50 50 50Persons 26275 14022.5 26275 14022.5 17500 8775 14022.5

Passenger minutes 92375.63 32933.49 74222.08 36916.38 44423.08 25813.83 36916.38

Benefit / Loss - - 18153.55 -3982.89 22138.72 -3982.89

B L B L

Net Benefit / Loss 14170.66 18155.83

Table 5 Application of Davidsons Model for Two Directional Traffic in the Evening PeakTo Kandy Direction (PHF 7:00AM to 8:00PM)


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ENGINEER 16

5. Findings of the Study

From Table 4 it could be seen that theintroduction of a new mixed lane towardsColombo during the morning peak willhave a net reduction in travel time by14,170 passenger minutes during the peak

hour. If one of the in-bound lanes isdesignated to buses only, there will be areduction in travel time by 18,155passenger minutes. Hence converting alane towards Colombo direction isadvantageous, and if this lane isdesignated to buses only the advantage ishigher.

Similarly from Table 5 it could be seen thatthe introduction of a new mixed lane forvehicles travelling out of Colombo in theevening peak will have a net reduction intravel time by 8,018 passenger minutesduring the peak hour. If one of the out-bound lanes is designated to buses only,there will be a reduction in travel time by10,867 passenger minutes.

It was found that introduction of areversible lane (mix or buses only) towardsColombo bound traffic was advantageousfrom 6:00AM to 9:00AM, since during thisperiod Colombo bound traffic volumeincreases above 2000 vph (see Figure 3).Therefore, a 4th lane towards Colomboduring this period is found to be beneficialto the system. Similarly, introduction of a4th lane for out-bound traffic which isabove 2000 vph from 5:30PM to 8:30PM(see Figure 3) is also beneficial.

6. Conclusions

From options (1) & (3), it is observed thatbenefits can be obtained by introduction ofreversible lanes during morning andevening peaks for mixed traffic, to enhancethe road efficiency during peak flows.

From options (2) & (4) results it is clear thatintroduction of designated lanes only forbuses will further improve the overallefficiency of the system. If buses onlylanes are introduced it is of the utmostimportance to reserve these lanes only for

buses as expected. To obtain the maximumbenefits it should be ensured that buseswill not enter the mixed traffic lanes. If this

enforcement is neglected it can end up as afailure as shown in [6].

When implementing the reversible flowlanes, careful attention should be paid tothe intersection at the turn-off to Biyagamaroad, and also to the terminal at New

Kelani Bridge roundabout to ensuresmooth flow of traffic at these criticalpoints.

If the proposed scheme is implemented,one operational advantage is that, sincethis road stretch is located adjoining thePeliyagoda Police Station, strictimplementation is possible with closesupervision from the Peliyagoda trafficpolice division.

It is important that when flow direction ischanged in reversible flow lanes, to pay theutmost care by the implementers towardsthe safety of the drivers during thetransition. It is also important that strictlane discipline be maintained by all driversfor obtaining maximum benefits whileensuring safety of all the road users.

References

1. Kadiyali, L. R., Traffic Engineering andTransport Planning, Khanna Publishers, 2-B, Nath Market, Nai Sarak, Delhi, India,1997.

2. Salter, R. J. and Hounsell, N. B., HighwayTraffic Analysis and Design, MACMILLANPress Ltd., London, 1996.

3. Khisty, C. J. and Kent Lall, B.,Transportation Engineering AnIntroduction 2nd Ed. Prentice-HallInternational, Inc., New Jersey, 1998.

4. Davidson, K. B., A Flow Travel timeRelationship for Use in TransportPlanning, Proceedings, Australian RoadResearch Board 3, 1966.

5. Blunden, W. R. and Black, J. A., The LandUse / Transportation System, 2nd Ed.Pergamon Press, Elmsford, NY, 1984.

6. Weerasekera, K. S., Trial Introduction of aBus Lane on A02: A Post-mortem,ENGINEER Journal of The Institution of

Engineers, Sri Lanka, Vol. 43, No. 03, pp.53-56, The Institution of Engineers, SriLanka, July 2010.


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17ENGINEER

Effectiveness of Traffic Forecasting on Pavement

Designs for Sri Lankan Roads

W. K. Mampearachchi and P. H. Gunasinghe

Abstract: Pavement design plays an important role in any improvement or rehabilitation. It is aresponsibility of the road design Engineer to ensure that he has come up with an effective design, sothat it will last for the design life. This effectiveness or the optimization is very important asotherwise it could lead to financial implications.

The method adopted for the design of flexible pavements is the TRL, Road Note 31. The two mainparameters considered in the design of the pavements under Road Note 31 are Cumulative Numberof Standard Axles (CNSA) (i.e. Traffic Class) and the sub-grade strength (i.e. California Bearing Ratio(CBR)% class).

In this research study, flexible pavement designs of recently rehabilitated or improved set of roadswere analyzed to check the effectiveness of the traffic forecasting on pavement design. As the sub-

grade strength of the pavements is a fixed parameter in all the cases, the only possible variable is theTraffic Class relevant to predicted CNSA.

It was found in the study that the actual traffic growth rates of different modes of traffic which travelsalong the selected roads is different to the predicted rates at the time of design. It has also been shownand statistically proved that the Equivalent Standard Axles (ESA) values actually applied on thesepavements by large trucks / heavy goods vehicles are significantly high, compared to the ESA valuesrecorded at the design stage. The authors have proposed a methodology to evaluate the effectivenessof traffic forecasting on pavement designs, and improvements to the present practice of pavementdesigns carried out by the Road Development Authority (RDA) and its presentation.

Keywords: Pavement Designs, Sri Lankan roads

1. IntroductionThe damage that vehicles cause to a roaddepends very strongly on the axle loads of thevehicles. For pavement design purposes thedamaging power of axles is related to astandard axle of 8.16 tonnes usingequivalence factors which have been derivedfrom empirical studies [1,2]

The method adopted for the design of flexiblepavements is similar to the Transport ResearchLaboratory (TRL), Road Note 31,[3]. The twomain parameters considered in the design ofthe pavements under Road Note 31 areCumulative Number of Standard Axles(CNSA) and the sub-grade strength [3]. Thedesign of rigid pavements is carried out as [4].The deterioration of paved roads caused bytraffic is due to both the magnitude of theindividual wheel loads and the number oftimes these loads are applied. For pavementdesign purposes, it is therefore necessary toconsider not only the total number of vehiclesthat will use the road, but also the vehiclewheel or axle loads. Hence, both traffic count

and axle load information are essential forpavement design purposes.

In many countries, road traffic is growingrapidly in volume and in the size and weightof the vehicles using the roads. As aconsequence, highway engineers concernedwith designing new roads or the strengtheningof existing roads require reliable informationabout the distribution of axle loads for existingtraffic as well as information on National orregional axle load trends. This information is

required, so that accurate forecasts can bemade of the axle loads that a road will have tocarry over its design life.

Eng. (Dr.) W. K. Mampearachchi, BSc.Eng.(Hons)(Moratuwa), MIE (Sri Lanka), MSCE (SouthFlorida), PhD (Florida), CMILT (UK), Senior Lecturer,Department of Civil Engineering, University Moratuwa,Katubedda, Moratuwa, Sri Lanka.Eng. P. H. Gunasinghe., B.Sc. Eng. (Moratuwa), M.Eng.(Highway & Traffic, Moratuwa), MIE(Sri Lanka), ChiefEngineer, Road Development Authority.



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ENGINEER 18

Since the pavement design plays an importantrole in any improvement or rehabilitation, it isa responsibility of the road design Engineer toensure that he has come up with an effectivedesign, so that it will last for the design life.This effectiveness or the optimization is veryimportant as otherwise it could lead tofinancial implications. If it is under designed,it will not last till the end of its design life,thereby incurring huge sums of money for theearly rehabilitation and maintenance.If it is over designed, that would also be anundesirable fact, as the cost over run on thiscould have been utilized to improve anotherfew kilometers of road.

2. Significance of the ProblemIf pavements are to be designed adequately,the importance of accurate knowledge aboutthe magnitude and frequency of the axle loadsbeing carried on the roads is self-evident.When any road project is being designed, orappraised at the feasibility stage, it isrecommended that a classified traffic countand an axle load survey of commercialvehicles are undertaken. Ideally, suchsurveys should be carried out several timesduring the year to reflect seasonal changes [5]in the numbers of vehicles and the magnitudeof the loads.

In the Sri Lankan context, it expends a largesum of money on the improvements and themaintenance of the existing road network.Every year, a substantial percent of GDP isallocated for the road sector. As far as thepresent economic situation of the country isconcerned, this allocation is inadequate tomeet the expenditure required for therehabilitation and improvements of the

present road network. Hence, the country hasto depend on foreign investments, grants andloans for the further improvements and thedevelopment of the road sector. The situationhas further worsened , as the country is facingan economic crisis. The allocated fundssometimes do not meet even the urgentrehabilitation and maintenance of the entireroad network.

In view of the above, there is a need to utilizethe limited allocated funds in an effective

manner. It is therefore, necessary to make surethat there are well disciplined procedures in

the planning, design, construction, monitoringand maintenance of the entire road network.

3. Present Practice of PavementDesign/Traffic Forecasting

Generally, for the rehabilitation or the roadimprovement projects funded by theGovernment of Sri Lanka, the pavementdesigns are done by the Road DevelopmentAuthority (RDA). The present method ofdesign is based on the Transport ResearchLaboratory method [3], but modified to suitlocal conditions. The method covers roadscarrying traffic up to 30 million standard axlesduring the design period [6]. Also, thespecifications for the materials to be used inthe various pavement layers are as specified inthe standard specifications of RDA.[7] It wasfound that in most of the occasions the ESAvalues have been assumed or else typicalvalues for ESA in designs for RDA roads havebeen used. Sometimes ADT/MCC data usedfor the designs were out dated. It was alsonoted that there is no standard or consistencyin the design reports. These depend on thedesign Engineer.

Despite, some improvements have been donefor the pavement designs by RDA; it is

normally assumed the year of construction(two to three years assumed from the designyear) and also uses ESA values recordedelsewhere due to the unavailability of ESAvalues on the particular road section.

1995 1997 2007

Assumed Design life(10 yrs)

Operation year(Assumed)

Design year

4. Calculation of Actual TrafficGrowth Rates

For each road section, the classified quantitiesof the traffic (Manual Classified Counts, i.e.

Figure 1 - Present Practice of PavementDesign/Traffic Forecasting of RDA


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19ENGINEER

MCC) for each category of vehicles arecollected for both the periods of design stageand in the recent past after the road section isopened for traffic. These are converted toADT using following factors.

4.1. Factors Used for Calculation of ADT

The Planning Division of the RDA, generallyuse expansion factors to convert MCC to ADTdepending on the hours of count of the MCC.Factor; 1.1 and 1.2 are usually used to convert16 hours and 12 hours MCC to ADTrespectively. Traffic volume counted in themanual classified count for a certain timeperiod is expanded to obtain the 24 hourstraffic volume using expansion factors derivedfor each district.

4.2 Calculation of Cumulative Number ofstandard Axles (CNSA)

From the factors derived from the AmericanAssociation of State Highway andTransportation Officials (ASSHTO) road testwhich enable the damaging power of axleloads of different magnitudes to be expressedin terms of an equivalent number of standardaxle loads, the number of axles of each type of

vehicle that will use the road during its designlife is equated to an equivalent number ofstandard axles [8].

The cumulative number of standard axles(CNSA) for the design period can bedetermined by the expression,

CNSA = 365 Pi [(1+ri)n1]

Where,

Pi = number of standard axles

per day as an average for

the 1st year after

construction for vehicle

type i

ri = rate of growth for vehicle

type i

m = number of types of vehicles

n = design life in years.

At the time of pavement design, the predictednumber of equivalent standard axles value

(Designed CNSA) has been estimated usingthe traffic volumes (ADT) and the averageESA values of different vehicle categories forthe road section concerned assuming that theparticular road section would be constructedand in operation after a few years (generallytwo to three years allowed).

4.3 Selection of Traffic Class & Sub GradeStrength Class

There are eight traffic classes (T1-T8) and six

sub grade strength classes (S1-S6) given inTRL, Road Note 31 (DOE, 1993). The trafficclass relevant to calculated CNSA can beselected accordingly. Similarly, sub gradeclass also can be selected as the CBR of subgrade is known

5. Methodology

In this research study, flexible pavementdesigns of recently rehabilitated or improvedset of roads were analyzed to check the

effectiveness of the traffic forecasting onpavement design. As the sub-grade strengthof the pavements is a fixed parameter in all thecases, the only possible variable is the TrafficClass relevant to predicted CNSA. In order totest the reliability of the prediction of CNSA,three Scenarios were selected. They wereselected based on the Equivalent StandardAxle (ESA), Manual Classified Counts (MCC)and Average Daily Traffic (ADT) data. RecentADT data and design ADT are associated inthe actual traffic growth rates.

The local funded and foreign funded roads areanalyzed separately because the traffic growthfactors used for foreign funded roads aredifferent to local funded roads(as they are twodifferent parties) and also there are slightchanges in calculating the pavement layers. Sothe main data required for this study is recentADT and recent ESA values of vehicle typesfor each selected road section. The other datarequired are number of lanes, lastimprovement & date of improvement and the

design data (i.e. design method, year, designlife, ADT, predicted year of operation, actualyear of operation, predicted vehicle growth

i =1 ri


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ENGINEER 20

rate, design CNSA and design pavementlayers).

Since the actual date (year) of operation afterrehabilitation / improvement is now known, amore realistic prediction could be made using

a new set of data. As such, a new CNSA wascalculated for the same design life. This wascounted from the actual date of operationusing the following scenarios.

Scenario 1:Calculation of CNSA using recent data (recentADT & ESA values) and with same (predictedr %), traffic growth rate used for the design(i.e. CNSA supposed to be carried during therest of the life).

Scenario

2:Calculation of CNSA using design data (ADT& ESA values used for the design) and withactual traffic growth rate calculated.

Scenario 3:Calculation of CNSA using recent data (recentADT & ESA values) and with actual trafficgrowth rate calculated.

6. Analysis of Results

ADT data at the design stage is essential tocalculate the traffic growth rate. There weremany road designs, which could not beselected, as some of the necessary informationwas not given in the design reports. Theinclusion of ADT and ESA values at thedesign stage are very important. Keyinformation should be given not only forresearch studies of this nature, but also for thecorrect engineering application at the time ofpavement construction.

Specially, under this study, other problemsencountered were the non availability of dateof design and anticipated period ofconstruction. These two dates or the years arerequired to calculate the CNSA values underdifferent scenarios. Therefore, collected datawere analyzed with respect to the particularroad section in the following manner;

a) Comparison of actual traffic growth ratesagainst the predicted rate using ADT &MCC data.

b) Comparison of ESA values used for thedesign with the recent ESA values.

c) Comparison of cumulative number ofstandard axles (CNSA) calculated underthree different scenarios against the designcumulative number of standard axle.

6.1 Comparison of Actual Traffic Growth

Rates

The calculated traffic growth factors for localfunded roads are given in Table 1. Growthrates for the medium and heavy goodsvehicles used for the design and the actualvalues are shown in figure 2. For the localfunded roads, the predicted traffic growth rateused for the designs was 5%, except for theDehiwalaMaharagama road for which 10%growth rate has been selected.

The calculated traffic growth factors for ADB

funded roads are tabulated in Table 2. Threedifferent growth factors have been used for thecalculation of CNSA at the design stage.These growth factors have been derived fromthe analysis done in the feasibility study. Theyare as follows;

i) Growth factor for the period, up toand including the year 2010.

ii) Growth factor for the period, from theyear 2011 to the end of the design life.

iii) Growth factor for generated traffic atcompletion of the road.

Similarly, actual growth factors for eachvehicle category was calculated for the periodbetween the operation of new surface and theend of design life using the ADT data collectedfrom Planning Division of RDA. Growthfactors for large and articulated trucks of theADB funded road sections are shown in Figure3.

-8.0

0.0

8.0

16.0

24.0

32.0

40.0

Pili.-Ma

h.

Seed-Udu.

CGHW

_Bal.

Will.Go

po.

CGHW

_Dod.

Maw.By

pass

Dehi.

-mah

.

Road section

Grow

thRa

te

Predict

M.Good

H.Good

Figure 2 - Traffic growth rates of medium goodsvehicles and heavy vehicles on local funded roads


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21ENGINEER

-20

-15

-10

-5

0

5

10

15

20

25

30

Pel.-Mada

m.

Weer.-Tis

sa

Mal.-Timb

ol.

Tissa-K'g

ama

Dick.-B

eli.

Amb.-Elpiti.

Pana.-B

andar.

Katu.-K'gala

Gam.-Nawa

.

Road

Gro

wthrate

Predict

Large Truck

Art. Truck

Figure 3 - Traffic growth rates of large trucks

and articulated trucks- ADB funded roads

Predicted growth factor for the medium buswas 8.9% for the period up to 2010 and it was7% between 2011 and the end of the designlife, for all the roads except on the Katugastota

Kurunegala Road. For that road section, it

was 7.3% and 5.7% respectively. For the largebus, predicted growth factor for the period upto 2010 was 5.2% and it was 4% for the periodbetween 2011 and end of the design life,whereas for the Katugastota KurunegalaRoad, it was 4.2% & 3.3% respectively. Actualgrowth factor calculated for medium bus isnegative for all the roads in the selected set ofroads except on the Gampola NawalapitiyaRoad which is 1.7%. The actual growth factorfor large bus is greater than the predicted

growth factor. The reason for the aboveobservations is that passenger transportregulations have imposed a ban on smallbuses on the roads and to replace them withlarge buses.

For the small trucks, predicted growth factorfor the respective periods are 9.8% and 7.7%except on the Katugastota Kurunegala Road(i.e. it is 5.5% and 4.3%). It seems that theactual growth factor for small trucks arehigher than predicted rates, whilst it is less

than the predicted growth rates for largetrucks. It was expected that the usage of threeaxle trucks and articulated trucks would beincreasing at and above 5.0% rate, over itsdesign life, on the road sections once those areimproved or rehabilitated. The results showthat the actual growth factors for both threeaxle and articulated trucks are significantlyhigher than predicted growth rates except fora couple of road sections. This has beenproved statistically, that there is a significancedifference at the 5% significance level between

the actual and predicted growth rates for both3-axle and articulated trucks.

Predicted growth factor for the medium buswas 8.9% for the period up to 2010 and it was7% between 2011 and the end of the designlife, for all the roads where on the Katugastota Kurunegala Road. For that road section, itwas 7.3% and 5.7% respectively. For the largebus, predicted growth factor for the period upto 2010 was 5.2% and it was 4% for the periodbetween 2011 and end of the design life,whereas for the Katugastota KurunegalaRoad, it was 4.2% & 3.3% respectively. Actualgrowth factor calculated for medium bus isnegative for all the roads in the selected set ofroads except on the Gampola NawalapitiyaRoad which is 1.7%. The actual growth factorfor large bus is greater than the predictedgrowth factor. The reason for the aboveobservations is that, passenger transportregulations have imposed a ban on smallbuses on the roads and to replace them withlarge buses. The negative growth factors arerarely obtained (as shown in Figures 2 & 3)when the recorded count for a particular typeof vehicle is less than the previous year/yearscount for same.

For the small trucks, predicted growth factorfor the respective periods are 9.8% and 7.7%except on the Katugastota Kurunegala Road(i.e. it is 5.5% and 4.3%). It seems that the

actual growth factors for small trucks arehigher than predicted rates, whilst it is lessthan predicted growth rates for large trucks. Ithas been expected that the usage of three axletrucks and articulated trucks would beincreasing at and above 5.0% rate, over itsdesign life, on the road sections once those areimproved or rehabilitated. The results showthat the actual growth factors for both threeaxle and articulated trucks are significantlyhigher than predicted growth rates except fora couple of road sections. This has been

proved statistically, that there is a significancedifference at the 5% significance level betweenthe actual and predicted growth rates for both3-axle and articulated trucks.

6.2 Comparison of ESA Values

The ESA values obtained from recent axle loadsurveys for the different vehicle categories, forthe local funded road links are tabulated inTable 3. ESA values of medium and heavygoods vehicles used for the design and the

actual values of same for the local fundedroads are shown in Figure 4.


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ENGINEER 22

As discussed previously, small buses on the

road links are significantly less and hence, thePlanning Division of RDA is reluctant tomeasure axle loads of small buses. Hence,most of the time, ESA values are not measuredfor small buses. ESA values of large busesseem to be almost equal to the ESA valuesrecorded at the design stage. It has beenstatistically proved using 5% level ofsignificance that the ESA values measuredduring recent axle load surveys for themedium goods vehicles and for the heavygoods vehicles are significantly highercompared to the values used at the designstage. This is an important finding in respectof the pavement strength as the damagingeffect for the pavement is more than four timeswhen ESA exceeds the value one.

0.00

2.00

4.00

6.00

8.00

10.00

Pili.-M

ah.

Seed-Udu.

CGHW

_Bal.

Will.G

opo.

CGHW

_Dod

.

Mawa

.Bypass

Dehi.

-mah

.

Road section

ESA

Design-M. Good A ct ua l-M. Good

Design-H. Good A ct ua l-H. Good

Figure 4 - ESA values of medium and Heavy

goods vehicles - local funded roads

The ESA values calculated from themeasurements taken during axle load surveyscarried out in the recent past, for the differentvehicle categories, for the ADB funded roadlinks are tabulated in Table 4. ESA values usedfor the design and the actual values for largeand articulated trucks are shown in Figure 5.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Pel.-M

adam

.

Weer.-Tis

sa

Mal.-Tim

bol.

Tissa-K'ga

ma

Dick.-Beli.

Amb.-Elpiti.

Pana.-Bandar.

Katu.-K'gala

Gam.-Nawa.

Road section

ESA

Design-L.Truck A ctual-L.Truck

Design-3Axl.Truck Actual-3Axl.Truck

Figure 5 - ESA Values of Large & ArticulatedTrucks- ADB Funded Roads

ItemNo.

Road Name Status Vehicle Category

Medium Bus

LargeBus

LargeGoods

veh

MediumGoods

veh

HeavyGoods

veh

Cars

1 Piliyandala - Maharagama Rd.

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual 6.0 2.4 0.6 1.0 12.2 0.1

2Seeduwa - Udugampola Rd.

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual -10.2 0.5 0.6 12.0 6.7 -

3CGHW Road at Balapitiya

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual -7.2 4.7 1.1 6.2 26.1 -

4William Gopallawa Mw. Kdy.

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual -20.8 3.9 -7.6 -3.0 0.9 -

5CGHW Road at Dodanduwa

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual -1.0 2.2 -2.3 3.5 12.8 -

6Mawanella Bypass

Predicted 5.0 5.0 5.0 5.0 5.0 5.0

Actual -9.2 -12.3 -7.6 4.3 35.0 -

7Dehiwala - Maharagama Rd. Predicted 10.0 10.0 10.0 10.0 10.0 10.0

Actual -29.4 4.9 -13.3 -4.1 9.4 -

Table 1 Traffic Growth Factors Local Funded Roads


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ItemNo.

Road Name Stage Vehicle Category

MediumBus

LargeBus

SmallTruck

LargeTruck

3-Axletruck

Articu.Truck

1

Pelmadulla-MadampeRoad (C-11)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.102011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -6.80 16.10 10.70 0.40 7.60 3.40

2

Weerawila-Kataragama(C-10,1)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -6.50 -3.60 -12.60 3.00 13.20 23.80

3

Malwatte,Gwela to

Timbolketiya Rd.(C-13)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -9.90 8.20 8.70 2.10 18.90 18.90

4

Tissa-Kataragama(C-10,2)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -11.60 4.00 4.20 -1.60 12.20 12.20

5

Dickwella-Beliatta(C-10,3)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -8.20 7.40 18.40 2.60 29.90 16.10

6

Ambalangoda-Elpitiya(C-5)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -10.60 6.90 10.40 6.30 27.80 16.1

7

Panadura-RathnapuraRd. (C-3)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 5.20 5.50 6.60

Actual -8.80 15.70 12.70 6.60 24.6 14.9

8

Katugastota-Kurunegala

(C-7)

upto 2010 7.30 4.20 8.00 5.50 5.80 5.80

2011-End 5.70 3.30 6.30 4.30 4.50 5.40Actual -7.30 9.80 8.80 2.50 13.40 10.50

9

Gampola-Nawalapitiya(C-8)

upto 2010 8.90 5.20 9.80 6.70 7.10 7.10

2011-End 7.00 4.00 7.70 6.30 6.60 7.90

Actual 1.70 11.80 10.30 11.70 2.60 -

Table 2 Traffic Growth Factors ADB Funded Roads


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ENGINEER 24

ItemNo. Road Name Stage Vehicle CategoryMediumBus

LargeBus

SmallTruck

L.Truck

3-Axletruck

Articu.Truck

1

Pelmadulla-MadampeRoad (C-11)

Design 0.045 0.146 0.035 2.323 0.867 1.001

Current 0.007 0.340 0.048 8.465 2.850 4.480

2

Weerawila-Kataragama(C-10,1)

Design 0.037 0.193 0.152 0.465 0.867 1.001

Current - 0.368 0.003 5.215 1.865 6.166

3

Malwatte,Godakawela toTimbolketiya Road (C-13)

Design 0.045 0.146 0.035 2.323 0.867 1.001

Current 0.007 0.340 0.048 8.465 2.850 4.480

4

Tissa-Kataragama (C-10,2)Design 0.037 0.193 0.152 0.465 0.867 1.001

Current - 0.368 0.003 5.215 1.865 6.166

5

Dickwella-Beliatta(C-10,3)

Design 0.026 0.076 0.008 0.282 0.867 1.001

Current 0.021 0.439 0.096 6.238 4.987 -

6

Ambalangoda-Elpitiya(C-5)

Design 0.016 0.057 0.011 0.810 0.867 1.001

Current 0.017 0.376 0.309 6.285 7.714 -

7

Panadura-RathnapuraRoad (C-3)

Design 0.065 0.216 0.093 3.224 0.867 1.001

Current 0.020 0.438 0.222 5.163 7.250 9.136

8

Katugastota-Kurunegala(C-7)

Design 0.115 0.450 0.162 4.115 0.867 1.001

Current 0.033 0.620 0.220 2.670 8.640 14.900

9

Gampola-Nawalapitiya(C-8)

Design 0.080 0.331 0.071 1.981 0.867 1.001

Current 0.034 0.432 0.165 2.190 3.418 5.886

ItemNo.

Road Name StageVehicle Category

Medium

Bus

Large

Bus

Large

GoodsVeh

Medium

Goodsveh

Heavy

Goodsveh.

1Piliyandala - Maharagama Road

Design 0.013 0.444 0.003 0.229 -

Current - 0.400 0.321 3.181 8.090

2Seeduwa - Udugampola road

Design 0.049 0.200 0.045 0.370 0.640

Current - 0.400 0.321 1.860 9.843

3CGHW Road at Balapitiya

Design 0.019 0.329 0.176 0.918 1.925

Current 0.020 0.438 - 4.220 8.141

4William Gopallawa Mw. Kandy

Design 0.103 0.704 0.036 1.316 6.728

Current - 0.580 0.003 3.537 4.578

5CGHW Road at Dodanduwa Design 0.019 0.329 0.176 0.918 1.925

Current 0.017 0.376 0.001 2.509 7.000

6Mawanella Bypass

Design 0.020 0.400 0.176 0.918 0.000

Current 0.169 0.400 0.010 0.864 5.950

7Dehiwala - Maharagama Road

Design 0.170 0.320 0.010 1.680 2.450

Current 0.013 0.370 0.105 2.563 8.290

Table 4 ESA Values Foreign Funded Roads

Table 3 ESA Values Locally Funded Roads


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Similarly, in the local funded road links, ESAvalues recorded for the medium bus is lessthan the ESA values recorded at the designstage. However, ESA values of large busesand small trucks are slightly higher than theESA values recorded at the design stage. It hasbeen statistically proved that the ESA valuesof large trucks are significantly high comparedto the values recorded at the design stage. Thisis a very important fact, mainly because of thenumber of large trucks using; A & B classroads are generally high and thereby create atendency to damage the pavement structurebefore the end of its design life.

It has also been statistically proved that recentESA values calculated for the three axle trucksand articulated trucks are significantly high

compared to the ESA values at design stage.However, this may not be a fact that can behighlighted as the ESA values used for thedesign are default values. These default ESAvalues have been applied when the totalnumber of a particular vehicle type was lessthan 10. This default ESA factor wascalculated from the average measured valueson roads where the number of vehiclesweighed was greater than 10.

6.3 Comparison of Cumulative Number of

Standard Axle (CNSA) Values

As discussed in the Methodology, CumulativeNumber of Standard Axles (CNSA) that wouldcarry or supposed to carry over therehabilitated or improved pavement werecalculated under three (03) different scenarios.

Scenario 1 associates the present condition oftraffic and it gives an indication as to whatwould be the result if the present condition oftraffic continues at the predicted rate. It alsoindicates that, for the 90% of the selected roadsections, the CNSA of scenario 1 is higher thanthe design CNSA.

Scenario 2 associates the design data and theactual growth rates, and it is applied over theactual design life. Its CNSA values are almostclose to the design CNSA.

Scenario 3 represents the present condition oftraffic and also the actual growth rate. TheCNSA values of it are higher compared to thedesign CNSA.

Comparison of CNSA values calculated undereach scenario against the designed CNSA, isdone for the local funded roads and for ADBfunded roads separately

The CNSA values calculated under eachscenario for the local funded roads are shownin the Table 5. The relevant traffic class withrespect to the CNSA value and its traffic classis also given for each road section forcomparison purposes. As shown in Table 5,except for the two roads section (i.e. WilliamGopallawa Mawatha, Kandy and Mawanella

Bypass Road) traffic class of Scenario-1 ishigher than the design traffic class.

It also shows that the traffic class of Scenario-3is higher than that of design traffic class,except for the William Gopallawa Mawathaand Dehiwala-Maharagama roads.

As discussed earlier, the ADT used for thedesign of William Gopallawa Mawatha roadwas over estimated. For the DehiwalaMaharagama road, the predicted traffic

growth rate for the design is twice comparedto others (i.e. r = 10%). These are the probablereasons for the above two exceptions.

A similar analysis could be done for the ADBfunded roads too, as per the results shown inTable 6. Except for two road sections, thetraffic class of Scenario-3 is higher than that ofdesign traffic class. The CNSA valuescalculated under each Scenario for the ADBfunded roads are shown in Table 6.


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ENGINEER 26

Table 5 CNSA Values of Each Scenario Local Funded Roads

Table 6 CNSA Values of Each Scenario ADB Funded Roads

Road Name

Pelmadulla-

MadampeRoad

(C11)

WeerawilaT

issa

[C10(1)]

Dickwella

Beliatta

(C10)

Ambalangoda

Elpitiya

(C5)

Panadura

Rathnapura

(C3)

Katugastota

Kurunegala

(C7)

Gampola

Nawalapitiya

(C8)

Tissa

Kataragama

[C10(2)]

Malwatte-

Timbolketiya

Road

(C13)

CNSADesign

4.98

(T5)

0.34

(T2)

0.0

(T1)

0.0

(T1)

8.88

(T6)

8.67

(T6)

5.00

(T5)

0.48

(T2) 3.9 (T5)

CNSA Scenario-1

9.66(T6)

1.49(T3)

3.13(T5)

4.48(T5)

16.57(T7)

6.8(T6)

11.53(T7)

0.9(T3)

8.25 (T6)

CNSA Scenario-2

3.21(T5)

0.12(T1)

0.0(T1)

0.0(T1)

6.98(T6)

8.16(T6)

7.39(T6)

0.0(T1)

2.62 (T4)

CNSA Scenario-3

10.47(T7)

1.1(T3)

6.47(T6)

9.48(T6)

--8.17(T6)

18.48(T8)

0.89(T3)

7.65 (T6)

Road Name

Piliyand

ala

Maharagama

Seeduw

a-

Udugam

pola

CGHW(1)

Balapitiya

William

GopallawaMw.,

Kandy

CGHW(

2)-

Dodand

uwa

Mawanelle-

Bypass

Dehiwala

Maharagama

CNSA designed0.75

(T3)

0.73

(T3)

3.9

(T5)

7.35

(T6)

3.6

(T5)

8.8

(T6)

9.65

(T6)

CNSA Scenario-1

0.92(T4) 8.61(T6) 10.15(T7) 7.23(T6) 6.8(T6) 5.22(T5)12.9(T7)

CNSA Scenario-2

0.83(T3) 1.18(T3) 2.69(T4) 5.4(T5) 3.61(T5) 5.56(T5)6.09(T6)

CNSA Scenario-3

13.68(T7) 14.27(T7) 14.67(T7) 5.91(T5) 7.23(T6) 15.08(T7)9.57(T6)


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7. Conclusion

In this research study, flexible pavementdesigns of recently rehabilitated or improvedset of roads were analyzed to check theeffectiveness of the traffic forecasting on

pavement design. As the sub-grade strengthof the pavements is a fixed parameter in all thecases, the only possible variable is the TrafficClass relevant to predicted CNSA. In order totest the reliability of the prediction of CNSA,the three Scenarios discussed above, wereselectedIt is better to look back at the three Scenariosdiscussed above.Scenario 1:Calculation of CNSA (Cumulative Number ofStandard Axles) using recent data (i.e. recent

ESA & ADT) and with same traffic growth rateused for the design.(CNSA supposed to carryduring the rest of the life)Scenario 2:Calculation of CNSA using design data (ESA& ADT used for the design) and with actualtraffic growth rate.

Scenario 3:Calculation of CNSA using recent data (recentESA & ADT) and with actual traffic growthrate.

The above Scenarios were selected based onthe ESA and ADT data. Recent ADT dataand design MCC / ADT are associated in theactual traffic growth rates.

Following conclusions were made with respectto the actual traffic growth rate and the ESAcomparison of each vehicle category.

It was observed that at or above 5% growthrates were predicted for both medium buses

and large buses. The actual traffic growth rateof medium buses was recorded as a negativerate and also for the large buses; actual growthrate is generally less than 5%. The probablereasons for these findings were discussedabove.

It can also be concluded that the growth rate ofheavy goods vehicles are higher than thepredicted rate. So, this study shows that thereis an increasing trend of commercial vehicleson the roads. It has also been shown and

statistically proved that the ESA valuesactually applied on these pavements by large

trucks / heavy goods vehicles are significantlyhigh, compared to the ESA values recorded atthe design stage. This could be an importantfactor that should be taken into account in thedesign of pavements as the damaging effect ofthe pavement increases heavily as the numberof heavy vehicles increased. In order, that thepavement designs of the selected road sectionsto be effective, the above factors or thefindings should be reflected in the designs.

Therefore, the most appropriate Scenariowhich incorporates all the key factorsidentified above has to be selected out of thethree Scenarios to test the effectiveness oftraffic forecasting of the selected set of roads.As such, it can be concluded that Scenario-3

is the most appropriate one to test theeffectiveness of traffic forecasting onpavement designs.

For twelve road sections, out of sixteen(i.e.75%), the traffic class related to Scenario-3is higher than the design traffic class. Hence, itcan be concluded that 75% of the selected roaddesigns are under designed.

Following recommendations are made inrespect of the conclusions made.

i) More emphasis should be given to theestimation of percentage of commercialtrucks (heavy goods vehicles).It is possible that this percentage couldsubstantially change during the periodbetween the actual traff

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