TE_5th sem 2007

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TRANSPORTATION ENGINEERING

TRAFFIC

ENGINEERING

PUBLIC

TRANSPORTATION

TRANSPORT

PLANNING

TRANSPORT

ECONOMICS

PAVEMENT

ENGINEERING

FUNCTIONAL CLASSIFICATION

ROADWAYS RAILWAYS WATERWAYS AIRWAYS

MODAL CLASSIFICATION

PUBLIC

CAR

ROADS

SIGNALS

PARKING LOTS

PUBLIC

TRAIN DRIVER

LOCO & COACHES

RAIL TRACKS

SIGNALS

STATIONS

PASSENGERS

CAPTAIN

SHIP

SHIPPING LINES

COAST GUARD

PORTS

PASSENGERS

PILOTS

AIRCRAFT

AIR ROUTS

AIR TRAFFIC CONTROL

AIR PORT

PASSENGERS

DRIVER

VEHICLE

WAY

CONTROL

TERMINAL

USER

ELEMENTAL CLASSES

FIGURE: CLASSIFICATION SCHEME USED FOR TRANSPORTATION ENGINEERING

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ROAD DEVELOPMENT IN INDIA

• In 25 – 35 B.C : MAHENJEDARO & HORAPPA• In 4TH Century B.C : ARYAN PERIOD

• In 5TH Century B.C : IMPERIAL GUPTA

• In 16TH – 18TH Century: MUGHAL EMPIRE

– Development of first class system of communication through a welldeveloped road system

– Major Routes were:• Patna – Kabul

• Delhi – Surat

• Delhi – Golconda

• Golconda – Bijapur • Bijapur – Ujjain

• Surat – Masulipatam

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• MODERN PERIOD

Under British Rule till the end of the 19th Century

First major reform in public road construction inaugurated during leadership of Lord

William Bentinck from 1828

A better era was followed during the rule of Lord Dalhousie (1848 – 56); PWD established

Road Development Committee (1927)

Under Mr. M. R. Jayakar, MLA, as chairman

The Road development committee known as Jayakar Committee

Set up November, 1927

Final report was published in November, 1928.

Recommendations

Road development should get National importance

Central Road Fund to be set up to generate revenue by additional

taxation on motor fuel, vehicle taxation, license fees for vehicles on hire A semi-official technical body should be formed

A research organization should be instituted to carry out research and

development work and to be available for consultations.

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Summery

Most of the recommendations of the Jayakar Committee were accepted by the

Govt.

Implementation

C.R.F – 1929

IRC - 1934 (semi official technical body)

CRRI- 1950 (a research organization)

Motor Vehicles Act – 1939 (revised in 1988)

Nagpur Road CongressChief Engineers of all States and Provinces were called by the Govt. of India tomeet at Nagpur in December, 1943 to discuss planning of post war road

development.

Known as 1st 20 years Road Development Plan in India (1943 – 1963)

Recommendations of Nagpur Road Plan

Road was classified in to four classes

1. National Highways: Traverse several provinces or states,

National Importance for Strategic, administrative and other

purpose

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2. State Highways: would be other main roads of states

3. District Roads: would take traffic from the main roads to the

interior of each district or similar unit- MDR, ODR

4. Village Road: which essentially farm tracks, to be designed,constructed and maintained under the authority of the State

Highways Department

Construction of NH – Central Govt.

Plan Period 20 years (1943-1963), target road length 16 km per 100 sq.

km. of agricultural area, planed decision were taken based on

agricultural and non-agricultural area.

Star and Grid pattern of road network considered

grid length for agricultural area – 16 km

grid length for non-agricultural area – 64 km

Bombay Road Plan ( 1961-1981) : 2nd 20 year road plan

Lucknow Road plan (1981- 2001) : 3rd 20 year road plan

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Present Road Development work in India

Function of National Highways Authority of India (NHAI) The National Highways Authority of India was constituted by an act of

Parliament, the National Highways Authority of India Act, 1988, It is responsible for the development, maintenance and management of National

Highways in India.

The NHAI is mandated to implement National Highways DevelopmentProject (NHDP)

India's Largest ever highways project- World class roads with uninterrupted traffic flow- Major initiative for capacity enhancement of National Highways- Four/Six Laning of around 13,146 Km- Total Cost Rs. 54,000 crores

In addition to implementation of National Highways Development Projects, the NHAIis also responsible for implementing some projects on National Highways other thanNHDP.NHAI is now responsible for implementing on National Highways of length

around 10,000 Km.

Up gradation of Rural Road Pradhan Mantri Gram Sadak Yojona

Based on Habitation of the Village

Core-network to be developed to connect the village through all weather road

Monitoring agency set up – State Technical Agency

Formulation and Planning – National Rural Road Development Agency Setup

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Indian ROAD NETWORKS

Indian road network of 33.4 lakh Km.is secondlargest in the world and consists of :

Types of Road network Length (in Km.)

EXPRESSWAYS 200

NATIONAL HIGHWAYS 66,590

STATE HIGHWAYS 1,28,000

MAJOR DISTRICT ROADS 4,70,000

RURAL AND OTHER ROADS 26,50,000

TOTAL LENGTH 33.4 LAKHS (APPROX.)

Status of National Highways as on

30

th

November, 2006

SingleLane/Intermed

iate lane

35%

Double Lane 55%

Four or morelanes

10%

About 65% of freight and 80% passenger traffic is carried by theroads

National Highways constitute only about 2% of the road networkbut carry about 40% of the total road traffic.

The growth of vehicles observed at an average pace of 10.16%per annum over the last five years.

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Figure: National Highways Development Projects in India

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“Transportation Engineering”

Transportation Engineering is the application of scientific process (like observation,

analysis and deduction) to the planning, design, operation and management of

transportation facilities.

Transportation Engineering is also multidisciplinary and require knowledge from

specialized fields such as psychology, economics, ecology and environment, sociology,

management, optimization, graph theory, probability theory, statistics, computer

simulation and other area of civil engineering (such as structural and geothecnical ).

Role of Transportation Engineering

The Institute of Transportation Engineers (1987) defines transportation engineering

as”the application of technological and scientific principles to the planning, functionaldesign, operation and management of facilities for any mode of transportation in order to

provide for the safe, rapid,comfortable, convenient, economical and environmentally

compatible movement of people and goods”.

Traffic Engineering, a branch of transportation engineering, is described as “thatphase of transportation engineering which deals with planning, geometric design, and

traffic operations of roads, streets and highways, their networks, terminals, abutting

lands and relationship with other modes of transportation”.

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Necessity of Highway Planning

Highway planning is a basic need for highway development. Particularly planning

is of great importance when the funds available are limited whereas the total requirement is

much higher.

Objective

To plan a road network for efficient and safe traffic operation, but at minimum cost.

To arrive at the road system and lengths of different categories of roads which could be

constructed within the available resources during the plan period under consideration.

To fix up date wise priorities for development of each road link based on utility as the

main criterion for phasing the road development program.

To plan for future requirements and improvements of roads in view of anticipated

development.

To work out financing system.

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Planning Surveys

Highway planning phases are:

Assessment of road length requirement for an area ( it may be a district, state

or the whole country)

Preparation of master plan showing phasing of plan in annual and or five year

plans

For assessing the road length requirement, field surveys are to be carried out to

collect the data required for determining the length of the road system.

The field (data) surveys thus required for collecting the factual data may be called as

planning surveys or fact finding surveys.

The planning surveys consists of the following studies:

A. Economic Studies

B. Financial Studies

C. Traffic or road user Studies

D. Engineering Studies

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A. Economic Studies

Population and its distribution in village, town or district or other locality with the

area classified groups

Population growth trend

Agricultural and Industrial products and their listing in classified groups, area wise

Future trend of agricultural and industrial development

Existing facilities with respect to communication, recreation and education etc.

Per capita income

B. Financial Studies

Essential to study the varies financial aspects like sources of income and the

manner in which funds for the project may be mobilized.

The Details are

Sources of income and revenue from taxation on road project

Living standard

Resources at local level, toll taxes, vehicle registration and fines – BOT

Future trends in financial aspects

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C. Traffic and Road Use Studies

All existing traffic details such as volume, flow pattern etc. to be collected before any

improvement could be planned.

Traffic survey should be carried out in the whole area and on selected routes andlocations and also by dividing the total route into homogeneous sections in order to

collect the following particulars.

Traffic Volume in Vehicle/day (ADT), annual average daily traffic (AADT), Peak hour

traffic and design hourly traffic volume.

Origin Destination Studies

Traffic Flow Patterns at junctions

Mass transportation facilities

Accidents, their causes, cost analysis

Future growth trend in traffic volume and goods traffic

Growth of passenger trips and the trend in the choice of mode

Axle load survey to find the axle load spectrum

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D. Engineering Studies

The engineering studies includes the followings

Topographic Survey – to create topographic Map for final alignment designSoil survey – soil investigation requires for design of pavement components etc.

Location and classification of existing roads

Road life studies

Traffic studies

Road Condition Survey – to evaluate the present structural condition of the road

Condition of bridge and culvert etc.

Special problems in drainage, construction and maintenance of road

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Classification of Rural Road – (IRC 73: 1980)

National Highway - NH

State Highway - SH

Major District Road - MDR

Other District Road - ODR

Village Road – VR

Classification of Urban Road – (IRC 86: 1983)

Arterial Road

Sub-arterial Road

Collector Street

Local Street

Road Patterns

o Rectangular or block pattern

o Radial or star and block pattern

o Radial or star and circular pattern

o Radial or star and grid pattern

o Hexagonal pattern

o Minimum travel pattern

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Highway Alignment

Layout of the Central Line of the highway on the ground is known as alignment

Horizontal alignment : Include Straight and horizontal curve

Vertical alignment : Gradient and vertical curve

Basic requirement of an ideal alignment

Short – Shortest between two terminals

Easy – Construction and maintenance of the highway must be easy

Safe – Should be safe against construction and maintenance, natural slope

stability, traffic operation with geometric features

Economical – Final cost should be minimum with respect to initial cost.

Methods of alignment survey

New Alignment – GIS method

Existing Alignment – Conventional method

Engineering Survey for Highway Location

Map Studies

Reconnaissance survey

Preliminary survey

Detail survey

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Detail survey

Establishing the Central Line of the proposed route

Establishing Bench Mark at suitable point

Detail survey of topography, soil investigation, leveling work etc.

Preparation of Drawing and Report

Key Map

Index Map

Preliminary Map

Detail plan and longitudinal profile

Detailed Cross-section

Land acquisition plans

Drawings of detail Cross drainage and other retaining structures

Drawings of road intersections

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HIGHWAY GEMETRIC DESIGN

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Highway Geometric Design

• Highway Geometric Design is an aspect of highway design dealing with thevisible dimensions of a roadway

• Proper designing of the layout of a road is important from two aspects:

It facilitates smooth flow of traffic and

It improves safety

These improvements derived from:

I. Good geometric design of direction changes in road

II. Good geometric design of slope changes in roads

III. Good delineation of desirable vehicular paths at confusing locations such as

intersections

Layout design of road sections joining two roads with different directions is

referred to as geometric design of horizontal curves

Layout design of road sections joining two roads with different gradients (or

slope) is referred to as geometric design of vertical curves

Layout design of road section for the purpose of proper delineation of vehicular

paths is referred to as channelization design

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Task of Geometric Design of highway

Cross Sectional Elements

Sight Distances

Horizontal AlignmentVertical Alignment

Intersection

Typical road cross-sectionFormation width

Carriageway

Right-of-way (ROW)

Roadway

G.L

Shoulder

Road Boundary

Building Line

Control Line

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Terrain Classification

Sl. No. Terrain Classification Percent Cross-slope of the country

1 Level/Plain 0 to 10

2 Rolling 10 to 253 Mountainous 25 to 60

4 Steep Greater than 60

The classification of the terrain is done by means of the cross-slope of the country.

Plain & Rolling Terrain Mountainous & Steep Terrain

For NH and SH

Single Lane 12.0 m. 6.25 m.

Two Lane 12.0 m. 8.80 m.

MDR

Single Lane 9.0 m. 4.75 m.

Two Lane 9.0 m. 4.75 m.

Road Way Width as per IRC

The minimum roadway width on single lane bridge is 4.25 m.

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Class of

Road

Plain and Rolling Terrain Mountainous Terrain

Rural Area Urban Area Rural Area Urban area

Normal Range Normal Range Normal Exceptional Normal Exceptional

NH

& SH

45 m (30 – 60) m 30 m (30 – 60) m 24 m 18 m 20 m 18 m

MDR 25 m (25 – 30)m 20 m (15 – 25) m 18 m 15 m 15 m 12 m

ODR 15 m (15 – 25) m 15 m (15 – 20) m 15 m 12 m 12 m 9 m

Right-of-way (ROW) width for different classes of Roads in India

Carriage way width

The width of the pavement is the carriage way width (Ref: IRC : 86-1983)

Class of Road Carriage way width (m)

Single Lane 3.75

Two lanes without raised kerbs 7.0

Two Lanes with raised kerbs 7.5

Intermediate Carriage way 5.5

Multilane Pavements 3.5 per Lane

The maximum width of vehicle as per IRC specification is 2.44 m.

Ref: IRC: 52 - 1981

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Shoulder

The shoulder is that part or portion of the roadway contiguous with traveled

way and is intended for accommodation of stopped vehicles, emergency use and

lateral support of base and surface course.

For Two lane rural roads shoulder width is 2.5 meter.Curbs (Kerbs)

A curb is a vertical or slopping member along

the edge of a pavement or shoulder strengthening or

protecting the edge and clearly defining the edge to

vehicle operators

Camber or cross-slope

Camber, also known as cross-slope facilitates drainage of a pavement laterally.

The amount of camber depends upon the smoothness of the surface and intensity of

rainfall

Fig. Vertical barrier curb

Types of Surface Camber in Percentage (rainfall heavy to light)

1. Cement Concrete or high type bituminous 2 to 1.7

2. Thin bituminous surfacing 2.5 to 2

3. Water bound macadam 3 to 2.5

4. Earth 4 to 3

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Sight Distances

• The clear visible distance available

• The sight distance requirements

# Stopping Sight Distance (SSD)# Overtaking Sight Distance (OSD)

# Intermediate Sight Distance

For operating a motor vehicle safely and efficiently, it is of utmost importance that drivers

have the capability of seeing clearly ahead. Therefore, sight distance of sufficient length

must be provided so that the drivers can operate and control their vehicle safely. Sight

distance – length of roadway ahead visible to the driver – can be discussed in four

important situations

1. The distances required by the motor vehicle to stop

2. The distances needed at complex location

3. The distances required for passing and overtaking vehicles, applicable to twolane highways

4. The criteria for measuring these distances for use in design

IRC recommended that the height of the driver’s eye is 1.2 m and height of the object is

0.15m above the road surface

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Sight Distances

Stopping Sight Distance (SSD)

Stopping sight distance is the distance required by a driver of a vehicle traveling at

given speed to bring his/her vehicle to a stop after an object on the highwaybecomes visible. It is made up of two components

i) the distance traveled during perception and break reaction time; and

ii) the distance travelled during the time the breaks are under application till the

vehicles comes to a stop

Perception time is the time which elapses between the instant the driver perceivesthe object on the carriageway and the instant that the realizes that breaking of the

vehicle is needed

The time lag or the brief interval between the perception of danger and the effective

application of the breaks is called break reaction time

As per IRC a value of 2.5 seconds is considered for perception time and break

reaction time taken together

Stopping Sight Distance = Distance travelled during perception and beak reaction

time + breaking distance (distance in which a moving

vehicle comes to a stop after the application of brakes)

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Stopping Sight Distance (SSD) = 278Vt + V2/(254f)

Where, V = Design Speed km/hr.

t = Perception and break reaction time

= 2.5 second

f = Coefficient of longitudinal friction between the

tyre and the pavement

SSD = in meter

The co-efficient of friction is assumed to vary from 0.40 at 20 kmph to 0.35 at 100 kmph

Effect of longitudinal grade

Stopping Sight Distance (SSD) = 278Vt + V2/254 (f + 0.1G)

G = gradient in percentage

positive sign may used for ascending gradient

negative sign may be taken for descending gradient

For single lane two-way traffic,

SSD = 2 [278Vt + V2/(254f )]Note: Correction for grade should not be applied on undivided roads with two-way traffic

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Speed

(Km/hr)

Safe Stopping Sight

distance (m)

20 20

25 25

30 30

40 45

50 60

60 80

65 90

80 120

100 180

Table: Stopping Sight Distance as per IRC

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Overtaking Sight Distance (OSD)

d1= represents the distance travelled during the perception and reaction time and

during the initial acceleration to the point of encroachment on the right lane

d2 = represents the actual distance covered by the overtaking vehicles during the

overtaking manoeuver

d3 = represents the distance between the overtaking vehicles at the end of its

manoeuver and the opposing vehicle, is known as clearance length

d4 = represents the distance travelled by an opposing vehicle at the design speed

while the overtaking manoeuver is taking place

d1 d2 d3 d4

Figure : Elements of Overtaking Sight Distance for two-lane highway

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d1 = vb t

s = (0.2 vb + 6)

d2 = (vb T + 2s)

d3 = vT

d4 = 2/3 (d2)

OSD = (d1 + d2 + d3 + d4)

= (d1 + 5/3d2 + d3 )

Therefore

OSD = 0.278 vb t +5/3(0.278vb T + 2s)+0.278VT

Where, vb = speed of overtaken vehicle, kmph

t = reaction time, sec,

V = speed of overtaking vehicle or design speed, kmph

T = √14.4s/A,sec = time taken for overtaking operations = spacing of vehicles = (0.2 vb + 6)

A = acceleration, kmph/sec

If the speed of overtaken vehicle vb is not given, the speed of overtaken

vehicle may be assumed as vb = (V – 16) kmph

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Minimum overtaking distance

For two-way traffic = (d1 + d2 + d3 + d4)

For one-way traffic = (d1 + d2)

On divided highway with four or more lanes, IRC suggests that normal OSD

is not necessarily be provided, only sight distance may be ensured which

should be more than the required SSD, which is absolute minimum sight

distance

OVERTAKING ZONE

The zones where the overtaking opportunity is available, zones which are

meant for overtaking.

The minimum length of overtaking zone:

For two-way traffic = 3 (d1 + d2 + d3 + d4)For one-way traffic = 3(d1 + d2)

The desirable length of overtaking zone is five times of the overtaking sight

distance

Speed Intermediate Sight

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Table: Overtaking Sight Distance as Per

IRC

Speed (Km/hr)Safe overtaking Sight

distance (m)

40 165

50 235

60 300

65 340

80 470

100 640

Table: Intermediate Sight Distance

Speed

(Km/hr)

Intermediate Sight

distance (m)

20 40

25 50

30 60

40 90

50 120

60 160

65 180

80 240

100 360

For the section of road where the overtaking sight distance can not be provided, as a

second preference, intermediate value between the safe SSD and safe OSD is

recommended

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Set-Back distance at obstructions of horizontal curve

The Value of Set-back distance M = S2 /8R

(for cases where the required sight distance is wholly within the curved road)

Figure: Elements of Set-Back distance at obstructions of horizontal curve

S

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R

mn

S

Sight Obstruction

SIGHT LINE

Fig. Visibility of Horizontal curve

R = radius of curve

S = Sight distance

m = minimum set- back distance

n = distance between centre line of

carriageway and centre line ofinside lane

Centre line of

carriage wayCentre line of

inside lane

Ref: IRC : 73-1980

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CALCULATION OF SET-BACK DISTANCE

The set-back distance is calculated from the following equation

m = R – (R-n) Cos

Where = [S / 2(R-n)] radians;

m = the minimum set-back distance to sight obstruction in meters

(measured from centre line of the road);

R = radius of centre line of the road in meters;

n = distance between the centre line of the road and the centre line of

the inside lane in meters; and

S = sight distance in meters

In the above equation, sight distance is measured along the middle of inner lane.

On single-lane roads, sight distance is measured along centre line of the roadand ‘n’ is taken as zero

Set-back distance for overtaking or intermediate sight distance can be computed

similarly but the clearance required is usually too large to be economically

feasible except on very flat curve

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Horizontal Alignment

Design of horizontal alignment consists of the following aspects such as

Design Speed

Horizontal CurveSuper elevation

Widening of pavement on horizontal curve

Horizontal Transition Curve

Design Speed

Design speed is a speed determined for design and correlation of the physical

features of a highway that influence vehicle operation. It is the maximum safe

speed that can be maintained over a specified section of a highway when

conditions are so favourable that the design features of the highway govern. The

design speed must be correlated with the terrain conditions as well as the

classification of highways.

The 95th and 98th percentile speed are frequently chosen at the Design Speed

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Horizontal Curve

A horizontal highway curve is a curve in plan to provide change in direction to the

central line of a road

The horizontal curve consists of

Horizontal Circular Curve


COMBINED CIRCULAR AND TRANSITION CURVE

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Superelevation

When a vehicle is moving on a curved path, it is subjected to an outward force,

commonly known as the centrifugal forces. In order to resist this forces, it is the usual

practice to super-elevate the roadway cross-section

The expression for super-elevation,

e + f = V2/ 127R,

V = Km/hr

R = Radius of the curve, m

e = super elevation, max value is 0.07 for plain and rolling terrain, for hill road notbounded by snow, max value is 0.10

f = Co-efficient of lateral friction, max value is 0.15

Coefficient of lateral friction depends on:

o Vehicle Speed

o Type and condition of road surface

o Type and condition of tyre

IRC suggested max value of f is 0.15

AASHTO suggested a max value of 0.16 for speed 50 kmph and min value of 0.08

for 120 kmph

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Equivalent Super elevation

Considering co-efficient of lateral friction = 0,

e = V2/127R,

In this condition pressure under both the wheel (inner and outer) will be same

As per the Indian practice, super-elevation is calculated on the assumption that it should

counteract the centrifugal force developed at three-fourth of design speed. Thus

e = (0.75V)2/127R

= V2/225R

Calculation for Super elevation

Step 01: Calculate the super elevation for 75% of design speed neglecting friction

Step 02: If calculated value of e is less than 0.07 for plain and rolling terrain, the value so

obtained is provided,If the value of e exceeds 0.07 then provide max super elevation of 0.07 and go

to step 03

Step 03: Check the co-efficient of friction developed for the max value of e (e=0.07) at

the full value of design speed, f = (V2/127R – 0.07)

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if the value of f comes less than 0.15 the super elevation of 0.07 is safe for the design

speed

If not, calculate the restricted speed as given in step 04

Step 04: As an alternate to step 04 the allowable speed at the curve is calculated byconsidering the design co-efficient of lateral friction and the max value of e

e + f = 0.07 + 0.15 = V2/127R

Note:

Appropriate warning sign and speed limit regulation sign are installed to

restrict and regulate the speed at such curves where the safe allowable

speed is less than the design speed

For highways the curve should be designed without any speed restriction

Therefore the curve should be re-aligned for the curve maintained design

speed.

Radaii curves for which no super-elevation is required

The normal camber can be provided for the section where the super elevation

calculated is less than the camber

R = V2/225 e

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Practical Values of the super-elevation rate

The value of the super-elevation rate that can be used is dependent on many factors:

o The frequency of snowfall (in cold countries)

o The type of terrain

o The type of area (urban or rural)

o Frequency of slow moving vehicles

Considering the factors various codes suggested different maximum levels of super-elevation rate

Consider a stopped vehicle on the curveas shown in the fig, for its equilibrium

condition the following inequality will

satisfy,

mg sin θ ≤ f s, max × mg cos θ

tan θ ≤ f s, maxe < f s, max

f s, max is the maximum co-efficient of

side friction

AASHTO suggested, for low speed,

maximum friction value close to 0.3,

where as IRC suggest a value of 0.15

Fig. Free body diagram of a static

vehicle on a circular horizontal curve

mg sin θ

f s × mg cos θ

mg cos θ

mg

θ

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Practical Values of the super-elevation rate

AASHTO suggested, for low speed, maximum friction value close to 0.3

IRC suggests a value of side friction as 0.15, which is independent of speed. Thisindicates that the maximum value of e, (i.e. emax), that can be used is at least as high

as 0.15.

However the practical maximum limits of e, as suggested by IRC and AASHTO, are

much lower than this value.

AASHTO suggests using e values less than 0.1 with several other lower limiting values

which depend on the terrain and environmental factors.

IRC (IRC: 73 – 1980, IRC:86 -1983) suggests the following maximum limits on e

values:

For plain and rolling terrain and snow bound areas – 0.07

For hilly terrains (without snow) – 0.1

For urban roads with frequent intersection – 0.4

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ATTAINMENT OF SUPERELEVATION ON CIRCULAR CURVE

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Widening of pavement on horizontal curve

On horizontal curves, especially when they are not of large radii, it is common to

widen the pavement slightly more than the normal width. That is some extra width

has been introduced at the horizontal curve. This method is referred as extra

widening of pavement.

Causes:

The vehicle has rigid wheel base and only front wheels can turn, the rear

wheel do not follow the same path as that of the front wheels.

When the vehicle operating the speed higher than the design speed, the

super-elevation and the friction of the pavement can not fully counteract thecentrifugal force effect. In that case some transverse skidding may occur.

Therefore in that situation extra widening is necessary.

While overtaking at horizontal curve there is the tendency of the driver to

maintain a greater lateral clearance between two vehicles than on straight

path for ensuring safety.The extra width of the pavement on horizontal curve is depend upon

1. Length of the wheel base of the vehicle

2. Radius of horizontal curve negotiating

3. Psychological factor depending on speed and radius of curve

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The extra widening of pavement on horizontal curves is divided into two parts:

Mechanical widening – W m Psychological widening – W ps

Mechanical widening

The widening required to account for the off-tracking due to the rigidity of wheel

base is referred as mechanical widening ( W m ) and can be calculated as given

below:

W m = l 2 / 2R

Where, l = Length of wheel base, m.

R = Radius of horizontal curve, m

The mechanical widening calculated above is required for one vehicle negotiating a

horizontal curve along one traffic lane.Hence in a road having ‘n’ traffic lanes, as ‘n’ vehicles can travel simultaneously, the

total mechanical widening required is given below:

W m = n l 2 / 2R

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Table: Extra width of pavement at horizontal curve

Radius of curve (m)Extra width in meter

Single lane Two - laneUp to 20 0.9 1.5

20 to 40 0.6 1.5

41 to 60 0.6 1.2

61 to 100 Nil 0.9

101 to 300 Nil 0.6

Above 300 Nil Nil

For multi-lane roads, the extra widening is calculated by adding half the extra

width of two lane roads to each lane of multilane road

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Method of introducing extra widening on horizontal circular curve

The widening is introduced gradually from the beginning of the transition curve with

an uniform rate till the full value of designed extra width is reached at the end of thetransition curve where full value of super-elevation is also provided

The full value of designed extra width is continued throughout the circular curve and

decreased along the transition curve

Normally the extra width is equally distributed i.e., We /2 each on inner and outer sides of the curve

On sharp curves of hill roads the extra widening in full may be provided on inside of

the curve

On horizontal circular curve without transition curves, two-thirds of the designed extra

width is provided at the end of the straight section, i.e., before the start of the circular

curve and the remaining one-third is provided on the circular curve

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NEED FOR TRANSITION CURVE (Introduction)

When a vehicle traveling on a straight course enters a curve of finite radius it is

suddenly subjected to the centrifugal force which causes jerk/shock and sway. In

order to avoid this it is customary to provide a transition curve at the beginning of

the circular curve having a radius equal to infinity at the end of the straight and

gradually reducing the radius to the radius of the circular curve where the curve

begins. Incidentally, the transition portion is also used for the gradual application of

the super elevation and the curve widening

OBJECTIVE OF PROVIDING TRANSITION CURVE

1. Gradually introducing the centrifugal force effect

2. For easy streeting of driver on the curve with safety & comfort

3. To provide super-elevation gradually

TYPES OF TRANSITION CURVE

# Spiral OR Clothoid

# Lemniscates

# Cubic parabola

111

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111

Normally Transition curve are of Spiral or Clothoid

IRC recommends the use of spiral as transition curve in horizontal alignment as

the

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Design standards for vertical curves establish their minimum lengths for

specific circumstances. For highways, minimum length of vertical curve may

be based on sight distance, on comfort standards involving vertical

acceleration, or appearance criteria

Vertical curves are normally parabolas centered about the point of

intersection (P.I.) of vertical tangents they join

The parabola is selected as the vertical curve so that the rate of change of

grade, which is the second derivative of curve, will be constant with

distance.

H Hh

Length of summit curve

OSD

SSD

N = (n1 + n2)

+n1 -n2

Fig. Length of summit curve

P.I.

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Length of summ it curve for stopping s ight distance (SSD)

Two cases are to be considered in deciding the length:

1. When the length of curve is greater than the sight distance (L > SSD)

2. When the length of curve is less than the sight distance (L < SSD)

When L > SSD

The general equation for length L of the parabolic curve is

L =

Where,

L = Length of summit curve, m

S = Stopping sight distance, m

N = Deviation angle, equal to algebraic difference in grades

H = Height of eye level of driver above roadway surface, 1.2 m.

h = Height of object above the pavement surface, 0.15 m.

2)2h2H(

2 NS

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When L < SSD

The general equation for length L of the parabolic curve is

L = 2S -

Where,

L = Length of summit curve, m

S = Stopping sight distance, m


H = Height of eye level of driver above roadway surface, 1.2 m.

h = Height of object above the pavement surface, 0.15 m.

N

2)2h2H(

Length of summ it curve for safe overtaking s ight d istance (OSD)

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Length of summ it curve for safe overtaking s ight d istance (OSD)

or Intermediate sight dis tance

Two cases are to be considered in deciding the length:

1. When the length of curve is greater than the overtaking sight distance or

Intermediate sight distance (L > S)

2. When the length of curve is less than the overtaking sight distance or

Intermediate sight distance (L < S)

When L > S

L = NS2/ 8H ; substituting h = H

When L < S

L = 2S – 8H/N

Example of typical vertical alignment

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Example of typical vertical alignment

I.P.

I.P.Up hill

straight linegradient (+ve)

Crest/Summit

curve (Parabola)

Downhill

straight line

gradient (-ve)

Sag/Valley curve(Parabola)

Up hill

straight linegradient (+ve)

Fig. Typical vertical alignment

Valley curve

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Valley curve

The length of valley curve is designed based on two important consideration

1. Impact free movement of vehicles at design speed or comfort criteria

of the passenger

2. Availability of SSD under head lights of vehicles for night driving

The best shape of valley curve is a transition curve for gradually

introducing and increasing the centrifugal acceleration or radial

acceleration change acting downward as the allowable rate of change

of centrifugal acceleration govern the design of valley curve

Allowable rate of change of centrifugal/radial acceleration is 0.6 m/s3

Generally Cubic parabola is preferred for vertical valley curve

Length of valley curve

The length of valley curve is design based on two criteria

I. The allowable rate of change of centrifugal/radial acceleration is

0.6 m/s3 that is comfort criteria and

II. The head light sight distance of the vehicle for night driving

The higher of the two value is adopted for design

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The valley curve is made with full transition curve (no circular in between), two similar transition curve of equal length

In fig. Total length of valley curve is L, and length of two similar transition curve is LS = L/2

having minimum radius R at common point on the curve, K

1. Th e len gth o f v alley c urv e fo r c om fo rt c on dit io n is

L = 2 LS = 0.38 (NV3)1/2

Consideration : value of rate of change of centrifugal acceleration is taken as 0.6 m/s3

Where,


V = Design Speed, kmph

-n1 +n2

Length of valley curve, L

N

L/2 L/2

Fig. Length of valley curve

K

2 Length of valley curve for head light s ight d istance of the vehic le

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2. Length of valley curve for head light sight distance of the vehic le

This can be determined from the two condition

a. When the total length of valley curve L is greater than the stoppingsight distance (equal to head light sight distance of vehicle), L>SSD

b. When L is less than SSD, LSSD

L =)tan22( 1

2

S h

NS

h1 h1

S

N

S tan

Fig. Head light sight distancewhen L > S

Where,

Average Height of the head light, h1 = 0.75

The beam angle = 10

L = Total length of valley curve, m

Where,

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b. When L

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Problem#01

An ascending gradient of 1 in 50 meets a

descending gradient of 1 in 80. Determine

the length of summit curve for a design

speed 80 kmph. Assume all other data

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Problem#02

A valley curve is formed by a descending gradient of 1 in40 which meets an ascending gradient of 1 in 30.

Design the total length of valley curve if the design

speed is 80 kmph so as to fulfill both comfort condition

and head light sight distance for night driving, after calculating the SSD required

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TRAFFIC ENGINEERING

Definition

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Definition

Traffic Engineering, a branch of transportation engineering, is

described as “that phase of transportation engineering which deals with

planning, geometric design, and traffic operations of roads, streets and

highways, their networks, terminals, abutting lands and relationship

with other modes of transportation”.

The study of Traffic Engineering is sub-divided in to the following groupsTraffic Characteristics

Traffic Studies and analysis

Traffic operation – control and regulation

Planning and analysis

Geometric design

Administration and management

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Traffic Characteristics

o Road User Characteristics

o Vehicle Characteristics


Traffic Volume study

Speed Studies

Origin and destination (OD) study

Traffic Flow characteristics

Traffic capacity study

Parking study

Accident study

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Traffic operation – control and regulation

Traffic Planning and analysis

Geometric design

Administration and management

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Traffic Characteristics

Road User Characteristics

Physical Mental Psychological Environmental

Vision,

hearing

Knowledge,

Skill, etc.

Perception, Intellection,

Emotion, and Volition

(PIEVE time)

Atmospheric condition,

locality, traffic

streams

Vehicular Characteristics

Vehicle

Dimensions

Gross vehicle

weight andaxle weight

Power of

vehicle

Speed of

vehicle

Breaking

characteristics

Maximum dimensions of Road Vehicles

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Maximum dimensions of Road Vehicles

Dimension of

vehicle

Details

Maximum Dimensions, m

(excluding front & rear

bumper)

Width All vehicles 2.50

Height

a) Single-decked vehicle for normal

application b) Double-decked vehicle

3.80

4.75

Length

a) Single-unit truck with two or more

axles

b) Single unit bus with two or more

axlesc) Semi-trailer tractor combinations

d) Tractor and trailer combinations

11.00

12.00

16.0018.00

Ref: Dimensions and Weights of Road Design Vehicles, IRC:3 – 1983, Indian

Roads Congress, New Delhi, 1983


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Traffic Volume study

Objective

1. To select the priority for improvement and expansion of trafficfacilities

2. This study helps in planning and design of traffic control

methodology

3. Classified traffic volume count study ( IRC recommends 7days 24

hours for mid block and 16 hours for junction, for rural roads) is

needed for structural design of pavement, finding the capacity of

the roadway etc

4. Turning movement count is used to design the intersection, fixing

the traffic signal timing etc.

5. Pedestrian traffic volume study is used for design side walks or

foot path, pedestrian signal timing, foot over bridge etc.Methods

1. Mechanical counters

2. Manual Methods

Presentation of Traffic Volume Data

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Presentation of Traffic Volume Data

Average Daily Traffic (ADT)

It is the average volume of traffic counted for 7 days 24 hours or 3 days 24

hours (Ref: IRC 64; IRC: 109)

Annual Average Daily Traffic (AADT)

It can be calculated from the traffic survey conducted throughout the year of all

season or by multiplying the ADT with Seasonali ty Facto r

Charts showing hourly, daily and seasonal variation of traffic

Composition of different types of traffic

Flow volume diagrams at an intersection

Thirtieth highest hourly volume Design hourly volume

It is the hourly volume that will be exceeded only 29 times in a year and all

other hourly volume of the year will be less than this value, For Indian

condition design hourly volume (DHV) of 8 to 10% AADT has been suggested

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TRAFFIC COMPOSITION A NATIONAL HIGHWAY

Car / Jeep /Van

17.9%

2 Axle Truck14.6%

Multi Axle Truck

10.3%Bus

7.4%

Cycle Rickshaw2.8%

2 Wheelers

12.2%

Other Fast

0.1%

Bicycle

29.2%

3 Wheelers

5.3%

Agricultural Tractor

0.1%

Other Slow0.0%

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0 20 40 60 80 100 120

10

20

30

40

50

Number of Hours in one year with Traffic Volume Exceeding that shown

H o u

r l yT r af f i cV ol um e– p er c en t of ADT

3 0 T HHI GHE S

T H O UR

Stream flow fundamentals

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Stream flow fundamentals

Definition

Flow: Flow (q) is defined as the number of vehicles passing a specified

point or short section in a given period of time in a single lane. It isexpressed as vehicles/hour/lane

Free-flow speed (uf ) : It is that speed which exists when flows approaches

zero under free-flow condition.

Optimum speed (uO ) : It is that speed which exists under maximum flow

condition.

Density (k) : It is defined as number of vehicles occupying a section of roadway

in a single lane. It is expressed as vehicles/km./lane

Jam density (k j ) : It is that density that occurs when both flow and speed

approaches zero

Optimum density (k O ) : It is occurred under maximum flow condition

Speed, flow and density relationship

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k j

uf

Density

(veh/km)

Speed(km/h)

Flow (veh/hr)

Speed

(km/hr)

q m

u o

uo = Speed at maximum flow qm

Which is half of free-flow speed uf

k j = jam density

km = density at maximum flow qm

uf Speed-density

relationship

Speed-flow

relationship

Flow

(veh/hr/lane)

Density

(veh/km/lane)

k jko

q m

ko

u o

Flow-density

relationship

Speed studies

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p

Spot Speed

It is the instantaneous speed of a vehicle at a specified location

Time-mean speedIt is the average of the speed measurements at one point in space over a

period of the time. It is the average of a number of spot speed

measurements.

Space-mean speed

It is the average of the speed measurements at an instant of time over a

space

TE_5th sem 2007

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