traffic intro - Masenz world

Traffic Engineering 2013

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Definition:

The Institute of Traffic Engineers (ITE) defines traffic engineering as “That phase of engineering which deals with

planning, geometric design and traffic operations of roads and streets and highways, their networks, terminals,

abutting lands, relationships with other modes of transportation for the achievement of safe, efficient and

convenient movement of persons and goods”

Objective of traffic engineer

Safety: The Primary Objective

• The principal goal of the traffic engineer remains the provision of a safe system for highway traffic.

• 26000 fatalities in Iran on 2007.

• 40000 to 43000 in U.S

• Something like a civil war.

• The objective of safe travel is always number one and is never finished for the traffic engineer

Scope of the Traffic Engineering

It covers a wide range of study, analysis and planning, design and operation of traffic facilities and movements.

Some are

Traffic characteristics- user and vehicle

Traffic study- speed, volume, speed and delay, O-D study, parking and accident

Operation- sign, signal, marking, and regulation this you study

Design of intersection, parking facilities and lighting, etc in detail

Accident analysis and study

Research

Table below presents detail scope of the subject

Transportation Eng. Referenced Material Course Instructor@


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Interrelationship between human/ machinery/environmental elements

Along with national economical development Chinese urban automobiles are more and more. The rapid increase of

urban automobiles has caused serious traffic jam and urban environmental pollution. But degree of different traffic

vehicles polluted environment is different.

William Haddon developed a matrix that identifies risk factors before the crash, during the crash and after the

crash, in relation to the person, vehicle and environment (Table below]. Haddon described road transport as an ill-

designed “man machine” system in need of comprehensive systemic treatment. Each phase – pre-crash, crash and

post-crash – can be analyzed systematically for human, vehicle, road and environmental factors. The Haddon

matrix is an analytical tool to help in identifying all factors associated with a crash. Once the multiple factors

associated with a crash are identified and analyzed, countermeasures can be developed and prioritized for

implementation over short-term and long-term periods.



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The Haddon matrix

Pre-crash Crash

prevention

Crash Injury prevention

during the crash

Post-crash Life sustaining

Desired outpu1

l Work

Others

S ys~tem of trips

FACTORS

:VEHICLES AND EQUIPMENT

~nformation Roadworthiness

Attitudes Lighting

Impairment Braking

Police enforcement Handling

Speed management

Use of restraints Occupani restraints

Impairment Other satiety devices

Crash protective design

First-aid skil l Ease oi access

Access to medics Fire risk

Road and transport system

School

Shopping

Road El.rld environmen1

Road users

'1/eh ic!e

Read tratnc cras~es

Humm factors

Road and e,nvironmental

factors

Road design and roadl layout

Speed limits

Pedestr ian fac ili ties

Crash-proteclive roadside objects

Rescue facili lies

Congestion

Other consequences of transp:~rt

Vehicle factors


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Impact of human and vehicular characteristics on traffic planning

The traffic stream includes a combination of driver and vehicle behavior. The driver or human behavior being non-

uniform, traffic stream is also non-uniform in nature. It is influenced not only by the individual characteristics of

both vehicle and human but also by the way a group of such units interacts with each other. Thus a flow of traffic

through a street of defined characteristics will vary both by location and time corresponding to the changes in the

human behavior.

Road user characteristics- motorists, pedestrians, cyclists, street child playing or walking.

Road users characteristics can be categorized as – physical, mental, psychological and environmental

The physical characteristics can be permanent or temporary

Permanent are- vision and sensing, Hearing and smelling, Sex

Temporary are

Alcoholic effect, Drug effect, Fatigue and illness

Driver Characteristics

A driver’s decisions and action depend principally on information received through the sense. Researchers report

that about 99 percent of the information a driver receives is visual. A person with normal vision can perceive

peripheral objects within a cone having a central angle ranging up to about 1600. A driver increases the amount of

visual information received by movement of the head and eyes. Visual activity declines and the field of vision

narrows with advancing age, especially when lighting conditions are poor. Older drivers also tend to have more

difficulty in judging distance and distinguishing colors than young drivers.

Sounds of horns or skidding tires may alert a driver to an impending collision, and engine noise aids the driver as

well as pedestrians in judging vehicle speeds. Sound within a vehicle such as loud conversation or radio music may

mask the sounds of sirens, bells or other important warning devices.

Drivers may detect a fire or engine malfunction by their sense of smell. Hunger, thirst or discomfort may cause

drivers to change their trip pattern or stop.

Driver Perception and Reaction

Driver perception reaction time is defined as the interval between seeing, feelings or hearing a traffic or highway

situation and making an initial response to what has been perceived.

Traditionally, perception reaction time has been couched in term of perception, intellection, emotion and volition

termed PIEV time. Perception is the process of forming a mental image of sensation received through the eyes, ear

or other parts of the body. Intellection is another word for reasoning or using the intellect. Emotion is the affective

and subjective aspect of a person’s consciousness. It has to do with how person feels about a situation. More often

than not, emotion is detrimental to safe motor vehicle operation. Volition is the act of making a choice or decision.

Vehicle characteristics:

v Static---------dimension

v Dynamic---kinematics and kinetics

Size



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The type and size of vehicles influence turning radius, width of lane, overtaking operation, clearances for bridges,

tunnels and parking facilities.

Power performance of the vehicle: directly related to the kinematics of the vehicle. Power developed by the engine

should be sufficient to overcome all resistance to motion at the desired speed and to accelerate at any desired rate.

1. Rolling Resistance:

2. Air Resistance:

3. Grade Resistance:

4. Friction resistance

5. Internal resistance-Transmission loss

Traffic operations and Regulation

Regulation is "controlling human or societal behavior by rules or restrictions." Regulation can take many forms:

• legal restrictions promulgated by a government authority,

• self-regulation by an industry such as through a trade association,

• social regulation (e.g. norms),

These regulations are framed for: Safe and efficient movement of traffic and pedestrians. Regulations should be

related with the design of roads and facilities and safe traffic operations. They are implemented to improve the

traffic flow.

Regulations and laws can be achieved in four phases:

1. Driver control

2. Vehicle control

3. Flow control

4. General control

1. Driver control:

• Issue of license after training and tests

• There are : professional & non Professional type

• Category (10 ): A, B, C, D, E, F, G, H, I, J

• Renew every five years

• Drive should physically fit, has no diseases like epilepsy, mental illness, heart disease, giddiness or

fainting, deafness, colour blindness, night blindness etc.

2. Vehicle control:

• Vehicle registration: Zonal registration, number plate in different colour for different ownerships.

• should fulfill the requirements on physical dimensions, weight, load,

• Regular maintenance check up



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• Insurance: third party insurance

• Regulation should cover: seating arrangements and protection against weather for public services

vehicle

• Brake, steering, lights,

• Pollutions: noise, emission, etc.

• Route control, time control for transport vehicles

3. Flow control:

• Directional control

• Turning control

• Overtaking control

• One-way, speed limit, prohibitory, pedestrian controls etc.

4. Other General Control: reporting of accidents and traffic violation cases etc.

Traffic control devices- signs, signal and markings, traffic island

Traffic control device is the medium used for communicating between traffic engineer and road users. Unlike other

modes of transportation, there is no control on the drivers using the road. Here traffic control devices come to the

help of the traffic engineer. The major types of traffic control devices used are- traffic signs, road markings , traffic

signals and parking control

Different types of traffic signs are regulatory signs, warning signs and informatory signs.

1. Regulatory signs: These signs require the driver to obey the signs for the safety of other road users.

2. Warning signs: These signs are for the safety of oneself who is driving and advice the drivers to obey

these signs.

3. Informative signs: These signs provide information to the driver about the facilities available ahead, and

the route and distance to reach the specific destinations

Regulatory Signs

These signs give orders. They tell drivers what they must not do (prohibitory), or what they must do (mandatory).

Most of them take the form of a circular disc, although two signs, the Stop sign and the Give Way sign, have

distinctive individual shapes.

Most regulatory signs are the means of putting into practical effect the regulation or control of traffic. For example,

they may impose restrictions on speed, on the turning of traffic at a junction or on waiting.

The mandatory signs give instructions to drivers about what they must do, the Stop and Give Way sign being

examples. Most other mandatory signs such as the Keep Left sign are circular with a white symbol and border on a

blue background.

There are many types of prohibitory signs, which give instructions to drivers about what they must not do, signs

banning turns or entry being examples. Speed restriction signs, no stopping sign and signs for waiting restrictions

are further examples. Most are circular and have a red border.



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Warning signs

These warn drivers of some danger or difficulty on the road ahead. Most of them take the form of an equilateral

triangle with its apex uppermost.

Warning signs are used to alert drivers to danger or potential danger ahead. They indicate a need for extra caution

by road users and may require a reduction in speed or other manoeuvre.

Most warning signs are triangular in shape with a red border encompassing a black symbol on a white background.

The black symbol is normally a diagram of the hazard. Sometimes additional information is put onto a

supplementary plate below the main sign.

Information Signs

Most of these signs give drivers information to enable them to find their way to their destination. It is a varied

group of signs, but they are all either square or rectangular in shape.

Direction Signs

Direction signs are the largest group of Information Signs. These signs give drivers information to enable them to

find their way to their destination. Good direction signing helps:

• To reduce delay and frustration;

• To keep traffic flowing smoothly and safely through junctions;

• To promote commerce and tourism;

Road Markings—for detail dimensioning see book page 231

Road Markings are classified as follows:

• Transverse lines which are laid across the road at right angles to the flow of traffic:-

o Stop lines

o Give way lines

o Markings at pedestrian crossings

• Longitudinal lines which are laid along the road parallel to the flow of traffic.

o Lane Lines

o Barrier Lines

o Hazard Lines

o Traffic Island Markings

o Edge of Carriageway

o Marking for Parking Restrictions

o Traffic Lane Arrows

The purpose of road markings is to control, warn, or guide, road users. They may be used to supplement other

traffic signs or they may be used alone. Their major advantage is that they can give a continuing message to the

driver. Thus they can be used to guide drivers in the correct positioning of their vehicles so that the traffic flows

smoothly and safely. Some help clarify or emphasize the meaning of other signs. Improved road marking is often

the most cost-effective solution to traffic and accident problems.



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Traffic Signals

The primary purpose of a traffic signal installation at a road junction is to reduce conflict between traffic streams.

Conflict at a junction is manifest as an increase in delay and an increase in the accident rate. The installation should

be designed to achieve safety and efficiency within the confines of the available road space.

Traffic control is by means of red, amber and green light signals, supplemented by additional green, amber and red

arrow light signals and regulatory signs as necessary. The sequence signaling will be red, green, amber and red.

The instruction conveyed by each coloured light signal is defined as follows:-

Red light - Denotes that traffic is prohibited from proceeding beyond the stop line.

Green light - Indicates that vehicular traffic may proceed beyond the stop line, and may turn in any direction,

subject to the normal priority rules being observed and provided that the turn is not prohibited by a

supplementary light signal (red arrow) or a regulatory traffic sign.

Amber light - Conveys same prohibition as red signal except where vehicles are so close to the stop line that they

cannot safely stop before stop line, they should proceed. This phase is usually displayed for three

seconds.

Signals to control pedestrian movements:

Signal-controlled pedestrian crossings are appropriate at sites where traffic speeds are high or where pedestrian

flow is very heavy. Crossings with pedestrian signals can also be incorporated in junctions controlled by traffic

lights.

The light signals to be displayed on a pedestrian signal are red, green and flashing green. The instruction conveyed

by each coloured pedestrian signals is: -

Red Standing Man - Denotes that pedestrian are prohibited from crossing the road.

Green Walking Man - Denotes that pedestrians may cross the road with care.

Flashing Green Man - Denotes that pedestrian are prohibited from crossing the road except where they have

started to cross the road, in which case they should continue to cross the road.

Traffic Islands

A principle concern in channelization is the design of the islands. An island is a defined area between traffic lanes

for control of vehicle movements. Within an intersection area, a median or an outer separation is considered to be

an island. It may range from an area delineated by barrier curbs to a pavement area marked by paint.

Classification of Islands



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Traffic islands usually serve more than one function, but may be generally classified in three separate types:

1. Channelizing Islands - These are designed to control and direct traffic movement, usually turning.

2. Divisional Islands - These are designed to divide opposing or same direction traffic streams, usually through

movements.

3. Refuge islands - Pedestrian islands are provided to serve as safety zones for the aid and protection of persons on

foot. If a divisional island is located in an urban area where pedestrians are present, portions of each island can be

considered a refuge island.

Traffic Studies

Flow

There are practically two ways of counting the number of vehicles on a road. One is flow or volume, which is

defined as the number of vehicles that pass a point on a highway or a given lane or direction of a highway during a

specific time interval. The measurement is carried out by counting the number of vehicles, , passing a particular

point in one lane in a defined period . Then the flow expressed in vehicles/hour is given by

Variations of Volume

The variation of volume with time, i.e. month to month, day to day, hour to hour and within a hour is also as

important as volume calculation. Volume variations can also be observed from season to season. Volume will be

above average in a pleasant motoring month of summer, but will be more pronounced in rural than in urban area.

But this is the most consistent of all the variations and affects the traffic stream characteristics the least.

Weekdays, Saturdays and Sundays will also face difference in pattern. But comparing day with day, patterns for

routes of a similar nature often show a marked similarity, which is useful in enabling predictions to be made.

The most significant variation is from hour to hour. The peak hour observed during mornings and evenings of

weekdays, which is usually 8 to 10 per cent of total daily flow or 2 to 3 times the average hourly volume. These

trips are mainly the work trips, which are relatively stable with time and more or less constant from day to day.

Types of volume measurements

Since there is considerable variation in the volume of traffic, several types of measurements of volume are



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commonly adopted which will average these variations into a single volume count to be used in many design

purposes.

1. Average Annual Daily Traffic(AADT) : The average 24-hour traffic volume at a given location over a

full 365-day year, i.e. the total number of vehicles passing the site in a year divided by 365.

2. Average Annual Weekday Traffic(AAWT) : The average 24-hour traffic volume occurring on

weekdays over a full year. It is computed by dividing the total weekday traffic volume for the year by 260.

3. Average Daily Traffic(ADT) : An average 24-hour traffic volume at a given location for some period of

time less than a year. It may be measured for six months, a season, a month, a week, or as little as two

days. An ADT is a valid number only for the period over which it was measured.

4. Average Weekday Traffic(AWT) : An average 24-hour traffic volume occurring on weekdays for some

period of time less than one year, such as for a month or a season.

Speed

Speed is considered as a quality measurement of travel as the drivers and passengers will be concerned more about

the speed of the journey than the design aspects of the traffic. It is defined as the rate of motion in distance per unit

of time. Mathematically speed or velocity is given by,

where, is the speed of the vehicle in m/s, is distance traveled in m in time seconds. Speed of different

vehicles will vary with respect to time and space. To represent these variation, several types of speed can be

defined.

Spot Speed

Spot speed is the instantaneous speed of a vehicle at a specified location. Spot speed can be used to design the

geometry of road like horizontal and vertical curves, super elevation etc. Location and size of signs, design of

signals, safe speed, and speed zone determination, require the spot speed data. Accident analysis, road

maintenance, and congestion are the modern fields of traffic engineer, which uses spot speed data as the basic

input. Spot speed can be measured using an enoscope, pressure contact tubes or direct timing procedure or radar

speedometer or by time-lapse photographic methods.

Running speed

Running speed is the average speed maintained over a particular course while the vehicle is moving and is found

by dividing the length of the course by the time duration the vehicle was in motion. i.e. this speed doesn't consider

the time during which the vehicle is brought to a stop, or has to wait till it has a clear road ahead. The running



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speed will always be more than or equal to the journey speed, as delays are not considered in calculating the

running speed delay time - meJourney ti

Route ofLenght

Time Running

Route ofLength Speed Running ==

Journey speed

Journey speed is the effective speed of the vehicle on a journey between two points and is the distance between the

two points divided by the total time taken for the vehicle to complete the journey including any stopped time.

Uniformity between journey and running speeds denotes comfortable travel conditions.

delay includingjourney Total

Route ofLength SpeedJourney =

Time mean speed and space mean speed

Time mean speed is defined as the average speed of all the vehicles passing a point on a highway over some

specified time period. Space mean speed is defined as the average speed of all the vehicles occupying a given

section of a highway over some specified time period. Both mean speeds will always be different from each other

except in the unlikely event that all vehicles are traveling at the same speed. Time mean speed is a point

measurement while space mean speed is a measure relating to length of highway or lane, i.e. the mean speed of

vehicles over a period of time at a point in space is time mean speed and the mean speed over a space at a given

instant is the space mean speed.

Types of speed studies:

• Spot speed study

• Speed and delay study

Uses of Spot Speed study:

• Geometric design of roads

• Regulation and control of traffic operation;

• Analyzing the causes of accidents;

• Before and after study of improvement projects;

• Determining the problems of congestion in the road section;

• Capacity study

Uses of speed and delay study:

• Find cost of journey during economic study;

• Evaluate congestion, capacity, service level and improvement needs;



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• Traffic planning studies for the determination of travel time for carrying out trip assignments;

• Delay studies at intersection for traffic control devices.

These studies are carried out at major highways, high accident points, and congestion points, at traffic signal and

at points of future development.

Methods of spot speed study

ü Direct timing procedure for the spot speed determination:

• Simple method

• Two reference points are marked on the pavement at a suitable distance apart and an observer starts and

stops an accurate stopwatch as a vehicle crosses these two marks.

• From the known distance and measured time intervals spot speed is calculated;

• Large effects may occur due to the parallax effect;

• Reaction of individual observer may affect the result.

One observer stands at the first reference point and gives signal to the observer standing at last reference point

(with stopwatch).

ü Enoscope method:

It is a simple device consisting of L-shaped mirror box, open at both ends. It has a mirror set fixed at 45 degree to

the arms of the instrument as in figure.

Figure: Enoscope

ü c) Pressure contact tubes

In this method detectors are used to indicate the time of entering and leaving the base length by the vehicle.

ü Radar speed meter

This automatic device works on the Doppler principle that the speed of a moving body is proportional to the

change in frequency between the radio wave transmitted to the moving body and the radio wave received back. It

directly measures speed.



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ü Photographic and video camera method

Time-lapse camera photography has been used to determine the speed of the vehicles. In this method, photographs

are taken at fixed intervals of time on a special camera. By projecting the film on the screen, the passage of any

vehicle can be traced with reference to time.

Video camera also can be used to measure the speed of the vehicle.

Presentation and analysis of spot speed data

Spot speed depends on factors like volume and composition of traffic, geometric layout, and condition of the road,

environmental conditions, human and vehicle characteristics etc. Careful consideration is necessary while

presenting the data.

Tabular presentation: grouping of spot speeds into speed cases to facilitate easy computation.

Graphical presentation: (Histogram and cumulative frequency curves)

Modal speed: peak of the frequency curve. (Mode of the distribution)

Median Speed: 50th percentile speed

98th percentile speed: below this speed 98% of vehicles move, and it is taken as design speed for the geometric

design.

85th percentile speed: 85% of the vehicles move below this speed. It is used to establish upper speed limit for

traffic management. It is taken as limit of safe speed in the road.

15th percentile speed: 15% of vehicles move below this speed. It is used for determining minimum speed limit

for major highways.

Arithmetic mean or average spot speed: Summation of all variable speed divided by the number of

observations.

Moving observer method (floating car method or riding check method)

Three observers on a test vehicle:

First observer: counts opposite traffic using hand tallies.

Second observer: with two stopwatches records time for each individual delays (at intersections or on bridges) and

total time duration for the trip of predefined route.

Third observer: records the number of overtaking and overtaken vehicles.

It gives mean value of flow and speed over a section, rather than at a point.

Average volume [q] = [na+nw] /[ta+tw]

Where,

na = average numbers of vehicles during trips in opposite direction

nw = average no of vehicles overtaking minus overtaken



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ta= average journey time during trips against the stream

tw= average journey time

Density

Density is defined as the number of vehicles occupying a given length of highway or lane and is generally

expressed as vehicles per km. One can photograph a length of road , count the number of vehicles, , in one

lane of the road at that point of time and derive the density as,

The density is the number of vehicles between the point A and B divided by the distance between A and B.

Density is also equally important as flow but from a different angle as it is the measure most directly related to

traffic demand. Again it measures the proximity of vehicles in the stream which in turn affects the freedom to

maneuver and comfortable driving.

Derived characteristics

From the fundamental traffic flow characteristics like flow, density, and speed, a few other parameters of traffic

flow can be derived. Significant among them are the time headway, distance headway and travel time. They are

discussed one by one below.

Time headway

The microscopic character related to volume is the time headway or simply headway. Time headway is defined as

the time difference between any two successive vehicles when they cross a given point. Practically, it involves the

measurement of time between the passage of one rear bumper and the next past a given point.

Distance headway

Another related parameter is the distance headway. It is defined as the distance between corresponding points of

two successive vehicles at any given time. It involves the measurement from a photograph, the distance from rear

bumper of lead vehicle to rear bumper of following vehicle at a point of time.

Travel time

Travel time is defined as the time taken to complete a journey. As the speed increases, travel time required to

reach the destination also decreases and viceversa. Thus travel time is inversely proportional to the speed.

However, in practice, the speed of a vehicle fluctuates over time and the travel time represents an average

measure.



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Fundamental relations of traffic flow

Time mean speed ( )

time mean speed is the average of all vehicles passing a point over a duration of time. It is the simple average of

spot speed. Time mean speed is given by,

where is the spot speed of vehicle, and is the number of observations. In many speed studies, speeds

are represented in the form of frequency table. Then the time mean speed is given by,

where is the number of vehicles having speed , and is the number of such speed categories.

Space mean speed ( )

The space mean speed also averages the spot speed, but spatial weightage is given instead of temporal. This is

derived as below. Consider unit length of a road, and let is the spot speed of vehicle. Let is the time the

vehicle takes to complete unit distance and is given by . If there are such vehicles, then the average travel

time is given by,

If is the average travel time, then average speed . Therefore from the above equation,

where vehicle will have speed and is the number of such observations.



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Fundamental relations of traffic flow

The relationship between the fundamental variables of traffic flow, namely speed, volume, and density is called

the fundamental relations of traffic flow. This can be derived by a simple concept. Let there be a road with

length km, and assume all the vehicles are moving with km/hr.

This is the fundamental equation of traffic flow. Please note that, in the above equation refers to the space mean

speed.

Fundamental diagrams of traffic flow

The relation between flow and density, density and speed, speed and flow, can be represented with the help of

some curves. They are referred to as the fundamental diagrams of traffic flow. They will be explained in detail one

by one below.

Flow-density curve

The flow and density varies with time and location. The relation between the density and the corresponding flow

on a given stretch of road is referred to as one of the fundamental diagram of traffic flow. Some characteristics of

an ideal flow-density relationship is listed below:

1. When the density is zero, flow will also be zero,since there is no vehicles on the road.

2. When the number of vehicles gradually increases the density as well as flow increases.

3. When more and more vehicles are added, it reaches a situation where vehicles can't move. This is referred

to as the jam density or the maximum density. At jam density, flow will be zero because the vehicles are

not moving.

4. There will be some density between zero density and jam density, when the flow is maximum. The

relationship is normally represented by a parabolic curve as shown in figure 3



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Flow density curve

The point O refers to the case with zero density and zero flow. The point B refers to the maximum flow and the

corresponding density is . The point C refers to the maximum density and the corresponding flow is

zero. OA is the tangent drawn to the parabola at O, and the slope of the line OA gives the mean free flow speed, ie

the speed with which a vehicle can travel when there is no flow. It can also be noted that points D and E

correspond to same flow but has two different densities. Further, the slope of the line OD gives the mean speed at

density and slope of the line OE will give mean speed at density . Clearly the speed at density will be

higher since there are less number of vehicles on the road.

Speed-density diagram

Similar to the flow-density relationship, speed will be maximum, referred to as the free flow speed, and when the

density is maximum, the speed will be zero. The most simple assumption is that this variation of speed with

density is linear as shown by the solid line in figure. Corresponding to the zero density, vehicles will be flowing

with their desire speed, or free flow speed. When the density is jam density, the speed of the vehicles becomes

zero.



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Speed-density diagram

It is also possible to have non-linear relationships as shown by the dotted lines. These will be discussed later.

Speed flow relation

The relationship between the speed and flow can be postulated as follows. The flow is zero either because there is

no vehicles or there are too many vehicles so that they cannot move. At maximum flow, the speed will be in

between zero and free flow speed. This relationship is shown in figure

Speed-flow diagram

The maximum flow occurs at speed . It is possible to have two different speeds for a given flow.

Origin and destination study

In a transportation study, it is often necessary to know the exact origin and destination of the trips. Origin is



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defined as the place where the trip begins and destination is defined as the place where the trip ends.

The specific uses of O-D survey data:

• To determine the amount of by-passable traffic that enters a town, and thus establishes the need for a

bypass.

• To develop trip generation and trip distribution models in transport planning process

• To determine the extent to which the present highway system is adequate and to plan for new facilities

• To assess the adequacy of parking facilities and to plan for future

• To judge adequacy of existing route

• To plan transportation system, & other mass transit routes

• To locate express way or major route along desire.

• To locate new bridge as per traffic demand

• To locate intermediate stops for public transport

Methods of O-D survey:

1. Road side interview

2. License plate method

3. Return post card method

4. Tag-on-car method

5. Home interview method

Road side interview

1. Decide stations, take help of Traffic Police

2. Stop vehicle and fill the prescribed questionnaire on the spot.

3. Information: place & time of O-D; route location, stoppages, purpose, vehicle and number of

passengers.

4. This is quick method, but it may cause the delay for traffic flow and it needs sufficient space to

stop vehicles & take interviews.

2. License plate method

• Entire study area is cordoned and observers are stationed at all points of entry and exit on all

routes.

• Each party at the station notes the license plate number of the vehicles entering and leaving the

cordoned area and the time.

• Separate sheets are maintained for each direction.

• After collecting field data office computation if done by tracking the vehicle number and its time

of entering and leaving the cordoned area.

This method is quite easy and quick in field, but it involves a lot of office work.



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3. Return postcard method

• Prepaid business reply post cards with return address are distributed to the road users.

• Questionnaire to be filled is printed on the card along with the request for the cooperation.

• The received cards are analyzed and conclusions are drawn.

4. Tag on vehicle method

• Pre-coded card/tag is stuck on the vehicle as it enters the study area.

• When the car leaves the cordon area tags are removed and recorded.

• Time of entering and leaving are recorded on the tag.

• Tags may be of different colour and shape for different routes.

5. Home interview Method

• O.5 to 10 % of the household is randomly selected for the home interview survey.

• Specific questionnaire is designed for the interview.

• Travel related data of household and socioeconomic data is collected.

Presentation of O-D data—figure- book p182

• Tables/matrix is prepared showing the number of trips between different zones.

• Desired lines are plotted which is graphical representation of O-D survey. Density of the desire lines

shows actual desire of the road user.

• Pie chart: the relative magnitude of the generated traffic and geometrical relationships of the zones

involved represented by pie chart.

Parking

Parking is one of the major problems that is created by the increasing road traffic. It is an impact of transport

development. The availability of less space in urban areas has increased the demand for parking space especially

in areas like Central business district. This affects the mode choice also. This has a great economical impact.

Parking studies

Before taking any measures for the betterment of conditions, data regarding availability of parking space, extent of

its usage and parking demand is essential. It is also required to estimate the parking fares also. Parking surveys are

intended to provide all these information. Since the duration of parking varies with different vehicles, several

statistics are used to access the parking need.

Purpose of parking studies:



21 Prem N. Bastola

• To determine the congestion in the city or town areas

• To assess the suppressed parking demand

• To estimate the desires and demands of the public for parking facility

• To decide the capacity, location and type of future parking facilities

Parking surveys

Parking surveys are conducted to collect the above said parking statistics. The most common parking surveys

conducted are in-out survey, fixed period sampling and license plate method of survey.

1. In-out survey: In this survey, the occupancy count in the selected parking lot is taken at the beginning.

Then the number of vehicles that enter the parking lot for a particular time interval is counted. The

number of vehicles that leave the parking lot is also taken. The final occupancy in the parking lot is also

taken. Here the labor required is very less. Only one person may be enough. But we wont get any data

regarding the time duration for which a particular vehicle used that parking lot. Parking duration and turn

over is not obtained. Hence we cannot estimate the parking fare from this survey.

2. Fixed period sampling: This is almost similar to in-out survey. All vehicles are counted at the beginning

of the survey. Then after a fixed time interval that may vary between 15 minutes to i hour, the count is

again taken. Here there are chances of missing the number of vehicles that were parked for a short

duration.

3. License plate method of survey: This results in the most accurate and realistic data. In this case of

survey, every parking stall is monitored at a continuous interval of 15 minutes or so and the license plate

number is noted down. This will give the data regarding the duration for which a particular vehicle was

using the parking bay. This will help in calculating the fare because fare is estimated based on the duration

for which the vehicle was parked. If the time interval is shorter, then there are less chances of missing

short-term parkers. But this method is very labor intensive.

Ill effects of parking

Parking has some ill-effects like congestion, accidents, pollution, obstruction to fire-fighting operations etc.

Congestion: Parking takes considerable street space leading to the lowering of the road capacity. Hence, speed

will be reduced, journey time and delay will also subsequently increase. The operational cost of the vehicle

increases leading to great economical loss to the community.

Accidents: Careless maneuvering of parking and unparking leads to accidents which are referred to as parking

accidents. Common type of parking accidents occur while driving out a car from the parking area, careless

opening of the doors of parked cars, and while bringing in the vehicle to the parking lot for parking.

Environmental pollution: They also cause pollution to the environment because stopping and starting of

vehicles while parking and unparking results in noise and fumes. They also affect the aesthetic beauty of the

buildings because cars parked at every available space creates a feeling that building rises from a plinth of cars.



22 Prem N. Bastola

Obstruction to fire fighting operations: Parked vehicles may obstruct the movement of firefighting vehicles.

Sometimes they block access to hydrants and access to buildings.

On street parking

On street parking means the vehicles are parked on the sides of the street itself. This will be usually controlled by

government agencies itself. Common types of on-street parking are as listed below. This classification is based on

the angle in which the vehicles are parked with respect to the road alignment. As per IRC the standard dimensions

of a car is taken as 5 2.5 metres and that for a truck is 3.75 7.5 metres.

Parallel parking: The vehicles are parked along the length of the road. Here there is no backward movement

involved while parking or unparking the vehicle. Hence, it is the most safest parking from the accident

perspective. However, it consumes the maximum curb length and therefore only a minimum number of vehicles

can be parked for a given kerb length. This method of parking produces least obstruction to the on-going traffic on

the road since least road width is used. Parallel parking of cars is shown.

The length available to park number of vehicles, L =

30 parking: In thirty degree parking, the vehicles are parked at 30 with respect to the road alignment. In this

case, more vehicles can be parked compared to parallel parking. Also there is better maneuverability. Delay

caused to the traffic is also minimum in this type of parking. L = =0.58+5N

45 parking: As the angle of parking increases, more number of vehicles can be parked. Hence compared to

parallel parking and thirty degree parking, more number of vehicles can be accommodated in this type of parking.

From figure 4, length of parking space available for parking number of vehicles in a given kerb is = 3.54

N+1.77

60 parking: The vehicles are parked at 60 to the direction of road. More number of vehicles can be

accommodated in this parking type. From the figure 5, length available for parking vehicles =2.89N+2.16.

Right angle parking: In right angle parking or 90 parking, the vehicles are parked perpendicular to the

direction of the road. Although it consumes maximum width kerb length required is very little. In this type of

parking, the vehicles need complex maneuvering and this may cause severe accidents. This arrangement causes

obstruction to the road traffic particularly if the road width is less. However, it can accommodate maximum

number of vehicles for a given kerb length. An example is shown in figure. Length available for parking

number of vehicles is = 2.5N.

off street parking

In many urban centres, some areas are exclusively allotted for parking which will be at some distance away from

the main stream of traffic. Such a parking is referred to as off-street parking. They may be operated by either

public agencies or private firms. A typical layout of an off-street parking is shown—refer book.



23 Prem N. Bastola

Types of off street parking

1. Surface car parking

2. Multi – storey Parking

3. Roof Parking

4. Underground parking

Accident Study

The problem of accident is a very acute in highway transportation due to complex flow pattern of vehicular traffic,

presence of mixed traffic along with pedestrians. Traffic accident leads to loss of life and property. Road accidents

cannot be totally prevented but by suitable traffic engineering and management the accident rate can be reduced.

Objective of accident studies

Some objectives of accident studies are listed below:

• To study the causes of accidents and suggest corrective measures at potential location

• To evaluate existing design

• To compute the financial losses incurred

• To support the proposed design and provide economic justification to the improvement

suggested by the traffic engineer

Causes of road accidents

The various causes of road accidents are:

• Road Users - Excessive speed and rash driving, violation of traffic rules, failure to perceive traffic situation in

time, carelessness, fatigue, alcohol, etc.

• Vehicle - Defects such as failure of brakes, steering system, tyre burst.

• Road Condition - Skidding road surface, pot holes, ruts.

• Road design - Defective geometric design like inadequate sight distance, inadequate width of shoulders,

improper curve design, improper traffic control.

• Unfavorable weather condition

Accident data collection

The data collection of the accidents is primarily done by the police. Motorist accident reports are secondary data

which are filed by motorists themselves. The data to be collected should comprise all of these parameters:

• General - Date, time, person involved in accident, classification of accident like fatal, serious, minor

• Location - Description and detail of location of accident

• Details of vehicle involved - Registration number, description of vehicle, loading detail, vehicular defects

• Nature of accident - Details of collision, damages, injury and casualty

• Road and traffic condition - Details of road geometry, surface characteristics

• Accident cost - Financial losses incurred due to property damage, personal injury and Casualty



24 Prem N. Bastola

Accident analysis

Site Analysis

One of the most important tasks in traffic safety is the study and analysis of site-specific accident information to

identify contributing causes and develop site remediation measures that will lead to improved safety.

Once location has been statistically identified as “high-accident” location, detailed information is required in two

principal ways:

1. Occurrence of accident

2. Environmental and physical conditions

The best information on the occurrence of accidents is compiled by reviewing all accident reports for a given

location over a specified study period. This can be done using accident record. Environmental and physical

conditions are established by a through site investigation. Two primary graphical outputs are then prepared.

1. Collision diagram

2. Condition diagram

Collision diagram: for figure refer book- khanna justo p195.

A collision diagram is a schematic representation of all accidents occurring at a given location over a specified

period. Depending upon the accident frequency, the “specific period” usually ranges from one to three years.

Each collision is represented by a set of arrows, one for each vehicle involved, which schematically represents the

type of accident and directions of all vehicles. Arrows are generally labeled with codes indicating vehicle types,

date and time of accident, and weather conditions.

Condition diagram

A condition diagram describes all physical and environmental conditions at the accident site. The diagram must

show all geometric features of the site, the location and description of all control devices (signs, signals, markings,

lighting, etc.) and all relevant features of the road side environment, such as the location of carriage ways,

roadside objects, lane uses etc.

Safety measures

The ultimate goal is to develop certain improvement measures to mitigate the circumstances leading to the

accidents. The measure generally includes engineering, enforcement and education.

Measures for the reduction in accident rates

The various measures to decrease the accident rates may be divided into three groups:

1. Engineering

2. Enforcement “3-Es”

3. Education

Engineering measures

a. Road design: The geometric design features of the road such as sight distances, width of pavement,



25 Prem N. Bastola

horizontal and vertical alignment and intersection design elements are checked and corrected if necessary.

The pavement surface characteristics are checked and suitable maintenance steps taken to bring them upto

the design standards.

b. Preventive maintenance of vehicle: The braking system, steering and lighting arrangements on vehicle may

be checked.

c. Before and after studies: After making the necessary improvement in design and enforcing regulation, it is

again collect and maintain the record of accidents “before and after” the introduction of preventive measures

to study their efficiency.

b) Road lighting: Lighting is particularly desirable at intersections, bridge sites and at places where there are

restrictions to traffic movements.

Enforcement measures

a. Speed control: Checks on spot speed of all fast moving vehicles should be done at selected locations and

timings and legal actions on those who violate the speed limits should be taken

b. Traffic control devices: Signals may be re-designed or signal system be introduce if necessary. Proper

traffic control device like signs, markings or channelizing island may be installed if necessary.

c. Training and supervision: the transport authorities should be strict in testing and issuing license to driver.

d. Medical check: The drivers should be tested for vision and reaction time at prescribed intervals.

e. Special precautions for commercial vehicles: having attendant to help and give proper direction to drivers of

heavy vehicles.

f. Observance of law and regulations: Traffic authorities should send study groups of trained personal, to

different locations to check whether the traffic regulations are being followed by the road users and also to

enforce the essential regulations.

Educational measures

a. Education of road users: The passengers and pedestrians should be taught the rules of the road, correct

manner of crossing etc.

b. Safety drive: Imposing traffic safety week when the road users are properly directed by the help of traffic

police and transport staff is a common means of training the public these days.

Road Intersection

Intersection is an area shared by two or more roads. This area is designated for the vehicles to turn to different

directions to reach their desired destinations. Its main function is to guide vehicles to their respective directions.

Basic requirement of intersection

1. Area of conflict should be minimum

2. Relative speed and angle of approach should be small

3. Adequate visibility



26 Prem N. Bastola

4. Sudden change of path should be avoided

5. Adequate geometric features such as turning radius

6. Proper sign, marking and good lighting for night visibility

Conflicts at an intersection—figure refer book p212

Conflict - It is defined as the demand for the same highway space by two or more users of the highway. Conflicts

are classified into mainly three types:

(a) Crossing conflicts

(b) Diverging conflicts

(c) Merging conflicts

Conflicts at an intersection are different for different types of intersection. Consider a typical four-legged

intersection as shown in figure. The number of conflicts for competing through movements are 4, while competing

right turn and through movements are 8. The conflicts between right turn traffics are 4, and between left turn and

merging traffic is 4. The conflicts created by pedestrians will be 8 taking into account all the four approaches.

Diverging traffic also produces about 4 conflicts. Therefore, a typical four legged intersection has about 32

different types of conflicts.

Types of intersection

The intersections are of two types. They are at-grade intersections and grade-separated intersections. In at-grade

intersections, all roadways join or cross at the same vertical level. Grade separated intersections allows the traffic

to cross at different vertical levels. Sometimes the topography itself may be helpful in constructing such

intersections. Otherwise, the initial construction cost required will be very high. Therefore, they are usually

constructed on high speed facilities like expressways, freeways etc. These type of intersection increases the road

capacity because vehicles can flow with high speed and accident potential is also reduced due to vertical



27 Prem N. Bastola

separation of traffic.

Grade separated intersections [ for figure see p 247]

Grade-separated intersections are provided to separate the traffic in the vertical grade. But the traffic need not be

those pertaining to road only. When a railway line crosses a road, then also grade separators are used. Different

types of grade-separators are flyovers and interchange. Flyovers itself are subdivided into overpass and underpass.

When two roads cross at a point, if the road having major traffic is elevated to a higher grade for further

movement of traffic, then such structures are called overpass. Otherwise, if the major road is depressed to a

lower level to cross another by means of an under bridge or tunnel, it is called under-pass.

Interchange is a system where traffic between two or more roadways flows at different levels in the grade

separated junctions. Common types of interchange include trumpet interchange, diamond interchange , and

cloverleaf interchange.

Trumpet interchange: Trumpet interchange is a popular form of three leg interchange. If one of the legs of the

interchange meets a highway at some angle but does not cross it, then the interchange is called trumpet

interchange.

Diamond interchange: Diamond interchange is a popular form of four-leg interchange found in the urban

locations where major and minor roads crosses. The important feature of this interchange is that it can be designed

even if the major road is relatively narrow.

Clover leaf interchange: It is also a four leg interchange and is used when two highways of high volume and

speed intersect each other with considerable turning movements. The main advantage of cloverleaf intersection

is that it provides complete separation of traffic. In addition, high speed at intersections can be achieved. However,

the disadvantage is that large area of land is required. Therefore, cloverleaf interchanges are provided mainly in

rural areas.

Channelized intersection [figure see p 237]

Vehicles approaching an intersection are directed to definite paths by islands, marking etc. and this method of

control is called channelization. Channelized intersection provides more safety and efficiency. It reduces the

number of possible conflicts by reducing the area of conflicts available in the carriageway. If no channelizing is

provided the driver will have less tendency to reduce the speed while entering the intersection from the

carriageway. The presence of traffic islands, markings etc. forces the driver to reduce the speed and becomes more

cautious while maneuvering the intersection. A channelizing island also serves as a refuge for pedestrians and

makes pedestrian crossing safer.

Traffic rotaries

Rotary intersections or round abouts are special form of at-grade intersections laid out for the movement of traffic

in one direction around a central traffic island. Essentially all the major conflicts at an intersection namely the



28 Prem N. Bastola

collision between through and right-turn movements are converted into milder conflicts namely merging and

diverging.

Advantages and disadvantages of rotary

1. Traffic flow is regulated to only one direction of movement, thus eliminating severe conflicts between

crossing movements.

2. All the vehicles entering the rotary are gently forced to reduce the speed and continue to move at slower

speed. Thus, none of the vehicles need to be stopped, unlike in a signalized intersection.

3. Because of lower speed of negotiation and elimination of severe conflicts, accidents and their severity are

much less in rotaries.

4. Rotaries are self governing and do not need practically any control by police or traffic signals.

5. They are ideally suited for moderate traffic, especially with irregular geometry, or intersections with more

than three or four approaches.

Disadvantages of rotary

1. All the vehicles are forced to slow down and negotiate the intersection. Therefore, the cumulative delay

will be much higher than channelized intersection.

2. Even when there is relatively low traffic, the vehicles are forced to reduce their speed.

3. Rotaries require large area of relatively flat land making them costly at urban areas.

4. The vehicles do not usually stop at a rotary. They accelerate and exit the rotary at relatively high speed.

Therefore, they are not suitable when there is high pedestrian movements.

Guidelines for the selection of rotaries

Because of the above limitation, rotaries are not suitable for every location. There are few guidelines that help in

deciding the suitability of a rotary. They are listed below.

1. Rotaries are suitable when the traffic entering from all the four approaches are relatively equal.

2. A total volume of about 3000 vehicles per hour can be considered as the upper limiting case and a volume

of 500 vehicles per hour is the lower limit.

3. A rotary is very beneficial when the proportion of the right-turn traffic is very high; typically if it is more

than 30 percent.

4. Rotaries are suitable when there are more than four approaches or if there is no separate lanes available for

right-turn traffic.

Traffic operations in a rotary [fig p 239]

As noted earlier, the traffic operations at a rotary are three; diverging, merging and weaving. All the other

conflicts are converted into these three less severe conflicts.

1. Diverging: It is a traffic operation when the vehicles moving in one direction is separated into different

streams according to their destinations.



29 Prem N. Bastola

2. Merging: Merging is the opposite of diverging. Merging is referred to as the process of joining the traffic

coming from different approaches and going to a common destination into a single stream.

3. Weaving: Weaving is the combined movement of both merging and diverging movements in the same

direction.

Design elements

The design elements include design speed, radius at entry, exit and the central island, weaving length and width,

entry and exit widths. In addition the capacity of the rotary can also be determined by using some empirical

formula. A typical rotary and the important design elements are shown in figure.

Design speed

All the vehicles are required to reduce their speed at a rotary. Therefore, the design speed of a rotary will be much

lower than the roads leading to it. Although it is possible to design roundabout without much speed reduction, the

geometry may lead to very large size incurring huge cost of construction. The normal practice is to keep the design

speed as 30 and 40 kmph for urban and rural areas respectively.

Entry, exit and island radius

The radius at the entry depends on various factors like design speed, super-elevation, and coefficient of friction.

The entry to the rotary is not straight, but a small curvature is introduced. This will force the driver to reduce the

speed. The entry radius of about 20 and 25 metres is ideal for an urban and rural design respectively.

The exit radius should be higher than the entry radius and the radius of the rotary island so that the vehicles will



30 Prem N. Bastola

discharge from the rotary at a higher rate. A general practice is to keep the exit radius as 1.5 to 2 times the entry

radius. However, if pedestrian movement is higher at the exit approach, then the exit radius could be set as same

as that of the entry radius.

The radius of the central island is governed by the design speed, and the radius of the entry curve. The radius of

the central island, in practice, is given a slightly higher radius so that the movement of the traffic already in the

rotary will have priority. The radius of the central island which is about 1.3 times that of the entry curve is

adequate for all practical purposes.

Width of the rotary

The entry width and exit width of the rotary is governed by the traffic entering and leaving the intersection and the

width of the approaching road. The width of the carriageway at entry and exit will be lower than the width of the

carriageway at the approaches to enable reduction of speed. IRC suggests that a two lane road of 7 m width should

be kept as 7 m for urban roads and 6.5 m for rural roads. Further, a three lane road of 10.5 m is to be reduced to

7 m and 7.5 m respectively for urban and rural roads.

The width of the weaving section should be higher than the width at entry and exit. Normally this will be one lane

more than the average entry and exit width. Thus weaving width is given as,

where is the width of the carriageway at the entry and is the carriageway width at exit.

Weaving length determines how smoothly the traffic can merge and diverge. It is decided based on many factors

such as weaving width, proportion of weaving traffic to the non-weaving traffic etc. This can be best achieved by

making the ratio of weaving length to the weaving width very high. A ratio of 4 is the minimum value suggested

by IRC. Very large weaving length is also dangerous, as it may encourage over-speeding.

Capacity

The capacity of rotary is determined by the capacity of each weaving section. Transportation road research lab

(TRL) proposed the following empirical formula to find the capacity of the weaving section.

where is the average entry and exit width, i.e, , is the weaving width, is the length of weaving,



31 Prem N. Bastola

and is the proportion of weaving traffic to the non-weaving traffic. and are the non-weaving traffic

and and are the weaving traffic.

Traffic Signal

These are control devices which direct the traffic to stop and proceed at intersections using red and green light

signal automatically. The conflicts arising from movements of traffic in deferent directions is solved by time

sharing of the facility. The advantages of traffic signal includes an orderly movement of traffic, an increased

capacity of the intersection and requires only simple geometric design. However the disadvantages of the

signalized intersection are it affects larger stopped delays, and the design requires complex considerations.

Although the overall delay may be lesser than a rotary for a high volume, a user is more concerned about the

stopped delay.

Advantages of signal

1. Provide orderly movement of traffic

2. Increase the capacity of at-grade intersections

3. Reduce accident specially right angled collision

4. Safety for pedestrians

5. Allow crossing of heavy vehicle with safety

6. Vehicle can maintain reasonable speed

7. More economical than manual operation

Disadvantages

1. Increase in rear-end collision can take place

2. Improper design may lead to violation of signal system

3. Failure due to electricity supply

Types of traffic signal

Fixed time signal traffic control signals

Manually operated signal

Traffic actuated signal

Pedestrian signal

Warrants for signal installation –p 221 book



32 Prem N. Bastola

Signal Design

Some basic terms in signal design

1. Cycle: A signal cycle is one complete rotation through all of the indications provided.

2. Cycle length: Cycle length is the time in seconds that it takes a signal to complete one full cycle of

indications. It indicates the time interval between the starting of of green for one approach till the next

time the green starts. It is given by the symbol "C".

3. Interval: Thus it indicates the change from one stage to another. There are two types of intervals – change

interval and clearance interval. Change interval which is also called the yellow time indicates the interval between

the green and red signal indications for an approach. Clearance interval which is also called "all red" is included

after each yellow interval indicating a period during which all signal faces show red and is used for clearing of the

vehicles in the intersection.

4. Green interval: It is the green indication for a particular movement or set of movements and is denoted

by G

5. Red interval: It is the red indication for a particular movement or set of movements and is denoted by R

6. Phase: A phase is the green interval plus the change and clearance intervals that follow it. Thus it is the

assigning of conflicting movements into separate groups. It allows a set of movements to flow and safely halt the

flow before another set of movements.

7. Lost time: It indicates the time during which the intersection is not effectively utilized for any movement.

Signal design procedure

The signal design procedure involves six major steps. They include the phase design, determination of amber time

and clearance time, determination of cycle length, apportioning of green time, pedestrian crossing requirements,

and the performance evaluation of the above design.

The objective of phase design is to separate the conflicting movements in an intersection into various phases, so

that movements in a phase should have no conflicts. If all the movements are to be separated with no conflicts,

then a large number of phases are required.


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1

General

1

Ø Important for night driving

ØAccidents and fatalities

ØMajor cause of accidents

Ø Poor night visibility

Ø Important at intersections, bridge site, level crossing

Ø Large no of pedestrian

ØUrban area- feeling of security and protection

2

Ø Road lighting- added facility

ØDuring night

Ø Visibility of object varies with absolute level of brightness

Ø Relative brightness of road surface and object

ØConcrete [light colored] pavements are better – it reflects light back

Ø Black top [ wet surface]- shiny/ mirror like do not reflect

Discernment by artificial lighting

3

ØDiscernment by silhouette

Ø Reverse silhouette

Ø Surface detail

ØArtificial lighting causes different degrees ofbrightness in the pavement and the objects.

Ø If the brightness of the object is less than that of thebackground [pavement] discernment of the object isby silhouette

4

} If the brightness of the object is more than that ofthe pavement – reverse silhouette

} In surface detail a portion of the object facing theobserver is illuminated by a high order of illuminationand other portions being less.

} Most common means – by silhouette

} The aim is to produce a bright surface on thepavement

} Pedestrians, cyclists and other objects should bevisible in the road.

Benefits

5

} A reduction in petty crime, personal robbery andburglary.

} An increased feeling of security for citizens.

} The opportunity for more night-time trading andcommercial activity.

} Making city centers more attractive, especially for visitorsand tourists.

} The creation of better driving conditions, especially fortwo-wheelers (with their inadequate lighting systems).

} An increased use of the road network at night, helping toreduce day-time and peak-hour congestion.

Factors affecting night visibility

6

Ø Size of object

Ø Brightness of object

Ø Brightness of background

Ø Reflecting characteristics of pavement

ØGlare on the eye of driver

Ø Time available to see the objects


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Design factors

7

Ø Lamps

Ø Luminaire distribution

Ø Spacing of lights

ØHeight of overhang of mounting

Ø Lateral placement

Ø Lighting layouts

Lamp

8

ØTypes

ØSize

ØColor

üEconomical to use largest lamp size in a luminaireto provide uniform brightness

üLuminance- candela/sqm- how bright the roadway is

üIlluminance- in lux- the amount of light incident on road

Lamp types

9

ØFilament

ØFluorescent- CFL tube light

ØSodium or mercury vapor- yellow color, halogen heater

ØLed lamp [ light emitting diode]- low power consumption

10

Luminaire – distribution of light

11

Ø Proper distribution of light

Ø Downward- high % of light is utilized for illuminating the pavement area

Ø Kerb + area 3 to 5 m beyond pavement edge

Ø 20 to 30 lux= average lux- in urban area

Ø 15 lux- other main road

Ø 4 to 8 lux- secondary roads

Indian code- average 30 lux

Minimum / avg illumination = 0.4

Spacing of light

12

Ø Electrical distribution of poles

Ø Property line

Ø Road layout

Ø Surrounding environment

} The wider the spacing of lanterns, the lower the level oflight and the more patchy it becomes.

} However, small spacing result in greater cost and are notalways practical.

} a ratio of Spacing to Mounting Height is given in codes toensure that minimum standards are achieved.


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Mounting

13

Ø Large and high mounting preferred

ØHeight of overhang 6 to 10 m

ØHigh values- less glare on eyes

ØMinimum vertical height above pavement surface = 6m for 650 volts

14

15 16

} The mounting height of a fixture is very important. It can affect the results of the design considerably.

} The horizontal illumination is inversely proportional to the square of the vertical distance, as measured from the light source.

Lateral placement

17

Ø Horizontal distance from the edge of pavement

Ø 0.6m from raised kerb

Lighting layout

18

ØOn straight road

Ø Single side

Ø Staggered on both sides

Ø Central

Ø Single side – easy to install economicalØ Suited to narrow roads

Ø Two lane roads

Ø 30 to 60m spacing


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19

Ø Staggered- for 3 or 4 or more lanes- 30 to 60m

Central- 30 to 40m

Ø Lighting on curve

Ø Closer spacing

Ø Outside of curve

Ø Intersection

Ø 25m interval

20

21 22

23

Cross roads

24


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25

Design

26

Ø Maintenance factor [MF]

Ø Light loss factors- denote the reduction of illumination for a given area after a period of time compared to initial illumination

Ø MF = luminaire lumen depreciation [LLD]* luminaire dirt depreciation [LDD]* equipment factor [EF]

Ø MF = 80% generally

27

Ø Utilization curve

Ø A plot of light falling on the horizontal surface both in front [street side and behind] and house side

Ø Shows the % of bare lamp lumen that falls on the horizontal surface

Ø Spacing = lamp lumen*CU*MF/ [avg lux* width of road]

Ø CU = coefficient of utilization

28

Design Example

29

ü Design a street lighting from the data below

ü Street width = 15m

ü Mounting height = 7.5m

ü Lamp size = 6000 lumen

ü Luminaire type = II

ü Average lux = 6

o Find the ratio = 2

o CU from graph = 0.44

o MF = 0.8

o Spacing = 23m


Traffic Engineering- Numerical BE

1 Prem N. Bastola/2013

* A police car A equipped with a radar capable of measuring the relative speed and relative

acceleration between it and another vehicle B is following a suspected speeding vehicle in a 40mi/hr

straight roadway. At the instant of interest the police car is accelerating at 8ft/sec2 from a speed of

50mi/hr. The radar reads VB/A = -5mi/hr and aB/A = -16 ft/sec2. Determine if the driver B was in

transgression.

**A vehicle approaches an intersection at 30 mi/hr. At t = 0 it begins to decelerate at a = 16ft/ sec 2

calculate the time it would take to stop the vehicle. Given that the beginning of deceleration the

vehicle was located 55ft from the stopping line, check if it was able to stop legally.

*** A driver of a car applied brakes and barely avoided hitting an obstacle on the roadway. The

vehicle left skid marks of 88 ft. assuming that f = 0.6, find if the driver was in violation of the 45 mi/hr

speed limit at the location if she was travelling uphill on a 3 degree incline, downhill on a 2.3 degree

incline and on a level roadway.

****A car stalled 50ft from the stopping line at an intersection to a signalized intersection of width =

40ft. the driver managed to start at the moment the traffic signal turned yellow and decided to clear the

intersection. Given that the car accelerated according to a = 4.8 – 0.06 ft/sec2 and minimum yellow

time = 4.5 seconds, perception reaction time = 1.0 sec, determine whether the driver was able to clear

the intersection on yellow.

***** Given that the relationship between speed and concentration obtained from the field data is v =

54.5 – 0.24k. Estimate the maximum flow, free flow speed and jam density.

****** A bicycle racer practices everyday at different times. Her route includes a ride along a 0.5 mi

bikeway and back. Since she is a traffic engineer, she had made it a habit to count the number of cars

in lane A that she meets while riding southward [Ms], the number of cars in lane A that overtake her

while riding northward [Mo] and the number of cars in lane A that she overtakes while riding

northward [Mp]. The details are given below in the table.

Time of day Ms Mo Mp

8 to 9 AM 107 10 74

9 to 10 113 25 41

10 to 11 30 15 5

11 to 12 79 18 9




Given that the bicycle travels at a constant speed of 20 mi/ hr find the traffic stream parameters for

each period of the day.

Problem # 1 A driver takes 3.2 seconds to react to a complex situation while travelling at a speed of 90

km/hr. How far does the vehicle travel before the driver initiates the physical response to the situation?

Problem # 2 A truck traveling at 40 kmph is approaching a stop sign. At time to and at a distance of

20m the truck begins to slow down by decelerating at 4 m/sec2. Will the truck be able to stop in time?

Problem # 3 an impatient car driver stuck behind a slow truck travelling at 32 kmph decides to

overtake the truck. The accelerating characteristics of the car is given by

dv/ dt = 1 – 0.04v where v = speed in m/sec and t = time in sec

find the acceleration after 2 3 10 and 300 seconds, the maximum speed attainable by the car, when

will the acceleration of the car approach zero, how far will the car travel in 300 seconds.

Problem # 4 The impatient driver approaches an intersection controlled by two way sign. The through

traffic is quite heavy with an average gap of 5 seconds. If this driver can accelerate his vehicle such

that dv/ dt = 1 – 0.04v and his perception reaction time is 0.75sec, find if he can clear the intersection.

take the width of the intersection as 7.5m and his car is 6m long

Problem # 5 in a braking test a vehicle travelling at a speed of 30 kmph was stopped by applying

brakes fully and skid marks were 5.8m in length. Find the average skid resistance of the pavement

Problem # 6 A vehicle travelling at 40 kmph was stopped within 1.8 sec after the application of the

brakes. Find the average skid resistance

Problem # 7 A vehicle moving at 40 kmph was stopped by applying the brakes and the length of the

skid marks was 12.2m, if the average skid resistance is 0.7 find the efficiency of the brakes.

Problem #8 If the spot speeds are 50, 40, 60, 54 and 45, then find the time mean speed and space mean

speed.

Problem # 9 In a field survey of spot speed measurement, the following observations were taken. Find

time mean speed and space mean speed and verify the relation

50, 40, 60, 54, 45, 31, 72, 58, 43, 52, 46, 56, 43, 65, 33, 69, 34, 51, 47, 41, 62, 43, 55, 40, 49




Problem # 10 The results of a speed study is given in the form of a frequency distribution table. Find

the time mean speed and space mean speed

Problem # 11 Find TMS and SMS for given data

Problem # 12 speed observations from a radar speed meter have been taken giving the composition of

volume of traffic and speed range. Find time mean speed, space mean speed and variance.

speed kmph 2--5 6--9

10--

13

14--

17

18--

21 22--25 26--29 30--33 34--37 38--41 42--45 46--49

50--

53

54--

57

58--

61

vehicle/hour 1 4 0 7 20 44 80 82 79 49 36 26 9 10 3

Problem # 13 The traffic in a congested multilane highway is observed to have an average spacing of

2000ft and average headway of 3.85 sec. find the rate of flow, density and speed in this lane.

Problem # 14 vehicle time headways and spacing were measured at a point along a highway, from a

single lane over the course of an hour. The average values were calculated as 2.5 s/veh for headway

and 60m/veh for spacing. Compute the average speed of the traffic.

Problem# 15 An observer counts 360 veh/hour at a specific highway location. Assuming that the

arrivals of vehicles is Poisson distributed, estimate the probabilities of having 0, 1 , 2,3,4 and 5 or

more vehicles arriving over a 20 second time interval.




Problem # 16 Consider the following spot speed data collected from a freeway site operating under

free-flow conditions.

a. Plot the frequency and cumulative frequency curves for these data

b. Find and identify on the curves, median speed, modal speed, 85th percentile speed, 15th and 98th

percentile speeds.

Speed

Group

[kmph]

No. of vehicles

observed [N]

15-20 0

20-25 3

25-30 6

30-35 18

35-40 45

40-45 48

45-50 18

50-55 12

55-60 4

60-65 3

65-70 0

Problem # 17 The length of a road stretch used for conducting the moving observer test is 0.5 km and

the speed with which the test vehicle moved is 20 km/hr. Given that the number of vehicles

encountered in the stream while the test vehicle was moving against the traffic stream is 107, number

of vehicles that had overtaken the test vehicle is 10, and the number of vehicles overtaken by the test

vehicle is 74, find the flow, density and average speed of the stream.

Problem # 18 Speed and delay studies by floating car method were conducted on a stretch of city road

of 3km length running north south. The data collected is given below. Find out

i. Average traffic volume

ii. Journey speed

iii. Running speed of the traffic system along either direction




No. of Vehicles

Trip

no

Direction

of Trip

Journey

time [min]

Total

Stopped

Delay [min]

Overtaking Overtaken

from

opposite

direction

1 N-S 5.5 1.5 4 7 250

2 S-N 6.25 1.67 5 5 200

3 N-S 5.36 1.5 5 3 240

4 S-N 6.33 2.25 3 1 230

5 N-S 5.63 1.16 2 6 230

6 S-N 6.3 1.33 2 3 250

7 N-S 5.33 1.67 2 7 210

8 S-N 6.53 1.83 3 2 180

9 N-S 5.16 1.5 2 4 200

Problem # 19 The spot speeds at a particular location are normally distributed with a mean of 51.7

kmph and a standard deviation of 8.3 kmph. Find the probability of

1 the speed exceeds 65 kmph

2. the speed lies between 40 to 70 kmph

3. the 85th percentile speed

Problem # 20 The free mean speed on a highway is found to be 100kmph. If the spacing of vehicle is

8m find the maximum flow.

Problem # 21 The spot speeds at a particular location on a highway are known to be normally

distributed with a mean of 80 kmph and a standard deviation of 15 kmph. Find the probability that if a

sample of 100 vehicles are tested the mean speed observed will exceed 75 kmph

Problem # 22 in a survey of spot speed at a given location of a highway it is desired to obtain an

average speed within 2 kmph with a probability of 95%. Previous studies have indicated that the

standard deviation of the speeds is 8 kmph. Compute the size of the sample.




Problem # 23 Estimate the theoretical capacity of a traffic lane with one way traffic flow at a stream

speed of 40 kmph if the average space gap between the vehicles is given by S = 0.278* Vt where Vt =

stream speed in kmph and t is average reaction time = 0.7 sec. assume average length of vehicle = 5m.

Problem # 24 A vehicle of 2000 kg skids a distance of 36 m before colliding with a stationary vehicle

of 1500 kg weight. After collision both vehicle skid a distance of 14 m. Assuming coefficient of

friction 0.5, determine the initial speed of the vehicle.

Problem # 25 Two vehicles A and B approaching at right angles, A from west and B from south

collide with each other. After collision vehicle A skids in direction 420 north of west and vehicle B,

580 east of north. The initial skid distance of vehicle A and B are 35 m and 25 m respectively before

collision. The skid distance after collision is 14m and 40 m respectively. If the weight of B and A are 6

tonnes and 4.4 tonnes Calculate the original speed of vehicle. The average skid resistance is 0.5.

Problem # 26 an isolated signal with pedestrian indication is to be installed on a right angled

intersection with road A 18 m wide and Road B 12m wide. The heaviest volume per hour for each lane

are 275 and 225 respectively. The approach speeds are 55 kmph and 40 kmph. Design the signal

Problem # 27 The 15 min count on cross roads A and B during peak hour are 178 and 142 vehicles per

lane. Assuming average head way of 2.5 seconds, design the signal by trial cycle method. Assume

suitable amber times

Problem # 28 The average normal flow on cross roads A and B during design period are 400 and 250

pcu per hour and the saturation flows are 1250 and 1000 PCU per hour. The all red time for pedestrian

crossing is 12 sec. Design the signal by UK method.

NB: if saturation flows are not given one may use S = 525 W where S = saturation flow and W =

width of approach road in m.

Problem # 29 Design a street lighting with the following data

Width of the road = 15m, Mounting height = 8m, lamp size = 6000 lumen and average lux = 6.

Problem# 30 Draw a four armed right angled intersection and show total number of conflicts if both

roads are two way, one road is two way and both roads have one direction flow. Classify the types of

conflicts. Consider pedestrian flow in all approaches.


Pavement Design 2013

1 Prem N. Bastola

Introduction to pavement design

A relatively stable layer constructed over the natural soil, for the purpose of supporting and distributing the wheel

load, providing an adequate surface for the movement of the vehicles

Objective

to provide a stable and even surface for the traffic, the roadway is provided with a suitably designed and

constructed pavement structure over a prepared soil sub-grade to serve as a carriageway.

Requirements of a pavement

An ideal pavement should meet the following requirements:

• Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil,

• Structurally strong to withstand all types of stresses imposed upon it,

• Adequate coefficient of friction to prevent skidding of vehicles,

• Smooth surface to provide comfort to road users even at high speed,

• Produce least noise from moving vehicles,

• Dust proof surface so that traffic safety is not impaired by reducing visibility,

• Impervious surface, so that sub-grade soil is well protected, and

• Long design life with low maintenance cost.

Types of pavements

The pavements can be classified based on the structural performance into two, flexible pavements and rigid

pavements. In flexible pavements, wheel loads are transferred by grain-to-grain contact of the aggregate through

the granular structure. The flexible pavement, having less flexural strength, acts like a flexible sheet (e.g.

bituminous road). On the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil by flexural

strength of the pavement and the pavement acts like a rigid plate (e.g. cement concrete roads). In addition to these,

composite pavements are also available. A thin layer of flexible pavement over rigid pavement is an ideal

pavement with most desirable characteristics

– Flexible pavement

– Rigid pavements

– Composite pavement

Flexible pavement Structure

– Surface course



2 Prem N. Bastola

– Base course

– Subbase course

– Subgrade

Flexible pavements

Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the

points of contact in the granular structure

Types of Flexible Pavements

The following types of construction have been used in flexible pavement:

• Conventional layered flexible pavement,

• Full - depth asphalt pavement, and

• Contained rock asphalt mat (CRAM).

Conventional flexible pavements are layered systems with high quality expensive materials are placed in the top

where stresses are high, and low quality cheap materials are placed in lower layers.

Typical layers of a flexible pavement

Typical layers of a conventional flexible pavement includes seal coat, surface course, tack coat, binder course,

prime coat, base course, sub-base course, compacted sub-grade, and natural sub-grade (Figure 2).

Seal Coat:

Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.

Tack Coat:

Tack coat is a very light application of asphalt, usually asphalt emulsion diluted with water. It provides proper

bonding between two layer of binder course and must be thin, uniformly cover the entire surface, and set very fast.

Prime Coat:

Prime coat is an application of low viscous cutback bitumen to an absorbent surface like granular bases on which

binder layer is placed. It provides bonding between two layers. Unlike tack coat, prime coat penetrates into the

layer below, plugs the voids, and forms a water tight surface.



3 Prem N. Bastola

Figure 2: Typical cross section of a flexible pavement

Surface course

Surface course is the layer directly in contact with traffic loads and generally contains superior quality materials.

They are usually constructed with dense graded asphalt concrete(AC). The functions and requirements of this layer

are:

• It provides characteristics such as friction, smoothness, drainage, etc. Also it will prevent the entrance of

excessive quantities of surface water into the underlying base, sub-base and sub-grade,

• It must be tough to resist the distortion under traffic and provide a smooth and skid- resistant riding

surface,

• It must be water proof to protect the entire base and sub-grade from the weakening effect of water.

Binder course

This layer provides the bulk of the asphalt concrete structure. It's chief purpose is to distribute load to the base

course The binder course generally consists of aggregates having less asphalt and doesn't require quality as high as

the surface course, so replacing a part of the surface course by the binder course results in more economical design.

Base course- The base course is the layer of material immediately beneath the surface of binder course and it

provides additional load distribution and contributes to the sub-surface drainage It may be composed of crushed

stone, crushed slag, and other untreated or stabilized materials.

Sub-Base course

The sub-base course is the layer of material beneath the base course and the primary functions are to provide

structural support, improve drainage, and reduce the intrusion of fines from the sub-grade in the pavement structure



4 Prem N. Bastola

Sub-grade

The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from the layers above. It is

essential that at no time soil sub-grade is overstressed. It should be compacted to the desirable density, near the

optimum moisture content.

Full - depth asphalt pavements are constructed by placing bituminous layers directly on the soil sub-grade. This

is more suitable when there is high traffic and local materials are not available.

Contained rock asphalt mats are constructed by placing dense/open graded aggregate layers in between two

asphalt layers. Modified dense graded asphalt concrete is placed above the sub-grade will significantly reduce the

vertical compressive strain on soil sub-grade and protect from surface water.

Rigid pavements

Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below.

Compared to flexible pavement, rigid pavements are placed either directly on the prepared sub-grade or on a single

layer of granular or stabilized material. Since there is only one layer of material between the concrete and the sub-

grade, this layer can be called as base or sub-base course.

Figure 3: Typical Cross section of Rigid pavement

.Types of Rigid Pavements

Rigid pavements can be classified into four types:

• Jointed plain concrete pavement (JPCP),

• Jointed reinforced concrete pavement (JRCP),

• Continuous reinforced concrete pavement (CRCP), and

• Pre-stressed concrete pavement (PCP).



5 Prem N. Bastola

Differences between flexible and rigid pavements

1. Deformation in the sub grade is

transferred to the upper layers

2. Design is based on load distributing

characteristics of the component layers

3. Have low flexural strength

4. Load is transferred by grain to grain

contact

5. Have low completion cost but repairing

cost is high

6. Have low life span

7. Surfacing cannot be laid directly on the

sub grade but a sub base is needed

1. Deformation in the sub grade is not

transferred to subsequent layers

2. Design is based on flexural strength or

slab action

3. Have high flexural strength

4. No such phenomenon of grain to grain

load transfer exists

5. Have low repairing cost but completion

cost is high

6. Life span is more as compare to flexible

7. Surfacing can be directly laid on the sub

grade

8. Thermal stresses are more vulnerable

8. No thermal stresses are induced as the

pavement have the ability to contract and

expand freely

9. Thats why expansion joints are not

needed

10. Strength of the road is highly dependent

on the strength of the sub grade

11. Rolling of the surfacing is needed

12. Road can be used for traffic within 24

hours

13. Force of friction is less.

to be induced as the ability to contract and

expand is very less in concrete

9. That why expansion joints are needed

10. Strength of the road is less dependent

on the strength of the sub grade

11. Rolling of the surfacing in not needed

12. Road cannot be used until 14 days of

curing

13. Force of friction is high

Factors affecting pavement design

There are many factors that affect pavement design which can be classified into four categories as traffic and

loading, structural models, material characterization, environment.

Traffic and loading

Traffic is the most important factor in the pavement design. The key factors include contact pressure, wheel load,

axle configuration, moving loads, load, and load repetitions.

Contact pressure:



6 Prem N. Bastola

The tyre pressure is an important factor, as it determine the contact area and the contact pressure between the wheel

and the pavement surface. Even though the shape of the contact area is elliptical, for sake of simplicity in analysis,

a circular area is often considered.

Wheel load:

The next important factor is the wheel load which determines the depth of the pavement required to ensure that the

subgrade soil is not failed. Wheel configuration affect the stress distribution and deflection within a pavement.

Many commercial vehicles have dual rear wheels which ensure that the contact pressure is within the limits. The

normal practice is to convert dual wheel into an equivalent single wheel load so that the analysis is made simpler.

Axle configuration:

The load carrying capacity of the commercial vehicle is further enhanced by the introduction of multiple axles.

Moving loads:

The damage to the pavement is much higher if the vehicle is moving at creep speed. Many studies show that when

the speed is increased from 2 km/hr to 24 km/hr, the stresses and deflection reduced by 40 per cent.

Repetition of Loads:

The influence of traffic on pavement not only depend on the magnitude of the wheel load, but also on the

frequency of the load applications. Each load application causes some deformation and the total deformation is the

summation of all these. Although the pavement deformation due to single axle load is very small, the cumulative

effect of number of load repetition is significant. Therefore, modern design is based on total number of standard

axle load (usually 80 kN single axle).

Structural models

The structural models are various analysis approaches to determine the pavement responses (stresses, strains, and

deflections) at various locations in a pavement due to the application of wheel load. The most common structural

models are layered elastic model and visco-elastic models.

Layered elastic model:

A layered elastic model can compute stresses, strains, and deflections at any point in a pavement structure resulting

from the application of a surface load. Layered elastic models assume that each pavement structural layer is

homogeneous, isotropic, and linearly elastic. In other words, the material properties are same at every point in a

given layer and the layer will rebound to its original form once the load is removed. The layered elastic approach



7 Prem N. Bastola

works with relatively simple mathematical models that relates stress, strain, and deformation with wheel loading

and material properties like modulus of elasticity and poissons ratio.

Material characterization

The following material properties are important for both flexible and rigid pavements.

• When pavements are considered as linear elastic, the elastic moduli and poisson ratio of subgrade and each

component layer must be specified.

• If the elastic modulus of a material varies with the time of loading, then the resilient modulus, which is

elastic modulus under repeated loads, must be selected in accordance with a load duration corresponding to

the vehicle speed.

• When a material is considered non-linear elastic, the constitutive equation relating the resilient modulus to

the state of the stress must be provided.

However, many of these material properties are used in visco-elastic models which are very complex and in the

development stage. This book covers the layered elastic model which require the modulus of elasticity and poisson

ratio only.

Environmental factors

Environmental factors affect the performance of the pavement materials and cause various damages.

Environmental factors that affect pavement are of two types, temperature and precipitation and they are discussed

below:

Temperature

The effect of temperature on asphalt pavements is different from that of concrete pavements. Temperature affects

the resilient modulus of asphalt layers, while it induces curling of concrete slab. In rigid pavements, due to

difference in temperatures of top and bottom of slab, temperature stresses or frictional stresses are developed.

While in flexible pavement, dynamic modulus of asphaltic concrete varies with temperature. Frost heave causes

differential settlements and pavement roughness. Most detrimental effect of frost penetration occurs during the

spring break up period when the ice melts and subgrade is a saturated condition.

Precipitation

The precipitation from rain and snow affects the quantity of surface water infiltrating into the subgrade and the

depth of ground water table. Poor drainage may bring lack of shear strength, pumping, loss of support, etc.

Methods of Flexible Pavement Design.

Empirical design



8 Prem N. Bastola

1. group index method

2. California Bearing Ratio (CBR) test [recommended by IRC] for graph p 351 book

3. CBR method by cumulative standard axle method

4. Asphalt institute method

5. Triaxial method

6. Burmister method .

Equivalent single axle load

Vehicles can have many axles which will distribute the load into different axles, and in turn to the pavement

through the wheels. A standard truck has two axles, front axle with two wheels and rear axle with four wheels. But

to carry large loads multiple axles are provided.

Legal axle load: The maximum allowed axle load on the roads is called legal axle load. For highways the

maximum legal axle load in India, specified by IRC, is 10 tonnes.

Standard axle load: It is a single axle load with dual wheel carrying 80 KN load and the design of pavement is

based on the standard axle load.

Equivalent axle load factor: An equivalent axle load factor (EALF) defines the damage per pass to a pavement by

the ith type of axle relative to the damage per pass of a standard axle load. While finding the EALF, the failure

criterion is important.

Assumptions in layered elastic model

The layered elastic approach works with relatively simple mathematical models and thus requires following

assumptions

_ Pavement layer extends infinitely in the horizontal direction

_ The bottom layer (usually the sub-grade) extends infinitely downwards

_ Materials are not stressed beyond their elastic ranges

Method 1,2 and 4 must be understood with numerical examples as discussed in class lecture

IRC method of design of flexible pavements [method no 3]

.Design procedure

Based on the performance of existing designs and using analytical approach, simple design charts and a catalogue

of pavement designs are added in the code. The pavement designs are given for subgrade CBR values ranging from



9 Prem N. Bastola

2% to 10% and design traffic ranging from 1 msa to 150 msa for an average annual pavement temperature of 35 C.

The later thicknesses obtained from the analysis have been slightly modified to adapt the designs to stage

construction. Using the following simple input parameters, appropriate designs could be chosen for the given

traffic and soil strength:

• Design traffic in terms of cumulative number of standard axles; and

• CBR value of sub-grade.

Design traffic

The method considers traffic in terms of the cumulative number of standard axles (8160 kg) to be carried by the

pavement during the design life. This requires the following information:

1. Initial traffic in terms of CVPD

2. Traffic growth rate during the design life

3. Design life in number of years

4. Vehicle damage factor (VDF)

5. Distribution of commercial traffic over the carriage way.

Initial traffic Initial traffic is determined in terms of commercial vehicles per day (CVPD). For the structural

design of the pavement only commercial vehicles are considered assuming laden weight of three tonnes or more

and their axle loading will be considered. Estimate of the initial daily average traffic flow for any road should

normally be based on 7-day 24-hour classified traffic counts (ADT). In case of new roads, traffic estimates can be

made on the basis of potential land use and traffic on existing routes in the area.

Traffic growth rate Traffic growth rates can be estimated (i) by studying the past trends of traffic growth, and (ii)

by establishing econometric models. If adequate data is not available, it is recommended that an average annual

growth rate of 7.5 percent may be adopted.

Design life For the purpose of the pavement design, the design life is defined in terms of the cumulative number of

standard axles that can be carried before strengthening of the pavement is necessary. It is recommended that

pavements for arterial roads like NH, SH should be designed for a life of 15 years, EH and urban roads for 20 years

and other categories of roads for 10 to 15 years.

Vehicle Damage Factor The vehicle damage factor (VDF) is a multiplier for converting the number of

commercial vehicles of different axle loads and axle configurations to the number of standard axle-load repetitions.

It is defined as equivalent number of standard axles per commercial vehicle.

Vehicle distribution

• Single lane roads: Traffic tends to be more channelized on single roads than two lane roads and to allow

for this concentration of wheel load repetitions, the design should be based on total number of commercial

vehicles in both directions.



10 Prem N. Bastola

• Two-lane single carriageway roads: The design should be based on 75 % of the commercial vehicles in

both directions.

• Four-lane single carriageway roads: The design should be based on 40 % of the total number of

commercial vehicles in both directions.

• Dual carriageway roads: For the design of dual two-lane carriageway roads should be based on 75 % of

the number of commercial vehicles in each direction. For dual three-lane carriageway and dual four-lane

carriageway the distribution factor will be 60 % and 45 % respectively.

Design traffic

The design traffic is considered in terms of the cumulative number of standard axles in the lane carrying maximum

traffic during the design life of the road. This can be computed using the following equation:

(3)

where is the cumulative number of standard axles to be catered for the design in terms of million standards

axle (msa), is the initial traffic in the year of completion of construction in terms of the number of commercial

vehicles per day, is the lane distribution factors, is the vehicle damage factor, is the design life in

years, and is the annual growth rate of commercial vehicles ( =-0.075 if growth rate is 7.5 percent per

annum). The traffic in the year of completion is estimated using the following formula:

(4)

where is the number of commercial vehicles as per last count, and x is the number of ears between the last count

and the year of completion between the last count and the year of completion of the project.

Pavement thickness design charts

For the design of pavements to carry traffic in the range of 1 to 10 msa, use chart 1 and for traffic in the range 10 to

150 msa, use chart 2 of IRC:37 2001. The design curves relate pavement thickness to the cumulative number of

standard axles to be carried over the design life for different sub-grade CBR values ranging from 2 % to 10 %.

Asphalt Institute Method [Flexible]

1. Cumulative ESALs is calculated

2. Design CBR is converted to sub-grade resilient modulus

MR (MPa) =10.3 x CBR



11 Prem N. Bastola

MR (Psi) = 1500 x CBR

3. From chart “full depth asphalt concrete” defines the total thickness of A/C corresponding to the ESAL and

MR.

Obtained full thickness of A/C is converted into the different layers (subbase and base) of other materials with

given modulus of elasticity, using the ratio;

t1, t2 = Thickness of layer 1 and 2 respectively

E1, E2 =Modulus of elasticity of layer 1 and 2 respectively



12 Prem N. Bastola

Rigid pavement design

As the name implies, rigid pavements are rigid i.e, they do not flex much under loading like flexible pavements.

They are constructed using cement concrete. In this case, the load carrying capacity is mainly due to the rigidity ad

high modulus of elasticity of the slab (slab action). H. M. Westergaard is considered the pioneer in providing the

rational treatment of the rigid pavement analysis.

Modulus of sub-grade reaction

Westergaard considered the rigid pavement slab as a thin elastic plate resting on soil sub-grade, which is assumed

as a dense liquid. The upward reaction is assumed to be proportional to the deflection. Base on this assumption,

Westergaard defined a modulus of sub-grade reaction in kg/cm given by where is the

displacement level taken as 0.125 cm and is the pressure sustained by the rigid plate of 75 cm diameter at a

deflection of 0.125 cm.

Relative stiffness of slab to sub-grade

A certain degree of resistance to slab deflection is offered by the sub-grade. The sub-grade deformation is same as

the slab deflection. Hence the slab deflection is direct measurement of the magnitude of the sub-grade pressure.

This pressure deformation characteristics of rigid pavement lead Westergaard to the define the term radius of

relative stiffness in cm is given by the equation .

(1)

where E is the modulus of elasticity of cement concrete in kg/cm (3.0 10 ), is the Poisson's ratio of

concrete (0.15), is the slab thickness in cm and is the modulus of sub-grade reaction.

Critical load positions

Since the pavement slab has finite length and width, either the character or the intensity of maximum stress

induced by the application of a given traffic load is dependent on the location of the load on the pavement surface.

There are three typical locations namely the interior, edge and corner, where differing conditions of slab continuity

exist. These locations are termed as critical load positions.

Equivalent radius of resisting section



13 Prem N. Bastola

When the interior point is loaded, only a small area of the pavement is resisting the bending moment of the plate.

Westergaard's gives a relation for equivalent radius of the resisting section in cm in the equation .

(2)

where is the radius of the wheel load distribution in cm and is the slab thickness in cm.

Wheel load stresses - Westergaard's stress equation

The cement concrete slab is assumed to be homogeneous and to have uniform elastic properties with vertical sub-

grade reaction being proportional to the deflection. Westergaard developed relationships for the stress at interior,

edge and corner regions, denoted as in kg/cm respectively and given by the equation - .

where is the slab thickness in cm, is the wheel load in kg, is the radius of the wheel load distribution in

cm, the radius of the relative stiffness in cm and is the radius of the resisting section in cm

Temperature stresses

Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. This is

caused by (i) daily variation resulting in a temperature gradient across the thickness of the slab and (ii) seasonal

variation resulting in overall change in the slab temperature. The former results in warping stresses and the later

in frictional stresses.

Warping stress

The warping stress at the interior, edge and corner regions, denoted as in kg/cm respectively

and given by the equation



14 Prem N. Bastola

where is the modulus of elasticity of concrete in kg/cm (3 10 ), is the thermal coefficient of concrete

per C (1 10 ) is the temperature difference between the top and bottom of the slab, and are the

coefficient based on in the desired direction and right angle to the desired direction, is the

Poisson's ration (0.15), is the radius of the contact area and is the radius of the relative stiffness.

Frictional stresses

The frictional stress in kg/cm is given by the equation

where is the unit weight of concrete in kg/cm (2400), is the coefficient of sub grade friction (1.5)

and is the length of the slab in meters.

Combination of stresses

The cumulative effect of the different stress give rise to the following thee critical cases

• Summer, mid-day: The critical stress is for edge region given by

• Winter, mid-day: The critical combination of stress is for the edge region given

by

• Mid-nights: The critical combination of stress is for the corner region given by



15 Prem N. Bastola

Bradbury coefficient computing Cx and Cy [ for stress calculation in rigid pavement]


3/19/2013

1

Failures of flexible and rigid pavements

Pavement Distress

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Pavement Performance

• The evaluation of pavement performance is animportant part of pavement design,rehabilitation and management.

• It includes the evaluation of distress,roughness, friction and structure.

• Traffic, materials and drainage can also beapplied to pavement evaluation.

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Factors affecting Pavement Performance

1. Traffic loading: Traffic volume, axle load, number ofequivalent single axle loads, tire pressure, truck typesaxle, configuration and load application time.

2. Material properties and composition: engineeringproperties of materials used in pavementconstruction: strength or bearing capacity, gradation,mix properties, elastic and resilient modulus, Poisson’sratio, etc.

3. Environmental factors: temperature, free and thaw,humidity and precipitation, ground water

4. Others: geometric features, drainage facilities,pavement structure, surface characteristics,construction joints

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Distress

• Distress is an important factor of pavement design.Unfortunately, many of the distresses are caused bythe deficiencies in construction, materials andmaintenance are not related directly to design.

• Knowledge of the various types of distress is importantto pavement designer because it can help them toidentify the cause of the distress.

• If distress is due to improper design, improvements inthe design method can be made.

• Furthermore, the evaluation of pavement distress is animportant part of the pavement management systemby which a most effective strategy for maintenance andrehabilitation can be developed

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Asphalt Pavement

• A typical pattern of deterioration in asphaltpavement is rutting, which developssomewhat rapidly during the first few yearsand then levels off to a much slower rate.

• Fatigue or alligator cracking does notnormally occur until after considerable loadingand then increases rapidly as the pavementweakens.

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• In climates with either large variations intemperature or very cold temperatures, asphaltpavements develop transverse and longitudinalcracks. These cracks usually break down and spallunder traffic.

• The most common problem with compositepavements is reflection cracking from joints andcracks in the underlying concrete slab.

• Infiltration if water into the cracks, along withfreezing, thawing and repeated loadings, usuallyresults in breakup and spalling of the asphaltsurface.

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Alligator or Fatigue Cracking

• Alligator or Fatigue Cracking is a series ofinterconnecting cracks caused by the fatigue failure ofasphalt surface under repeated traffic loading.

• The cracks propagate to the surface initially as one ormore longitudinal parallel cracks. After repeated trafficloading, the cracks connect and form many sided,sharp-angled pieces that develop a pattern resemblingthe skin of alligator.

• Alligator cracking is considered a major structuraldistress.

• Alligator cracking is measured in square feet or squaremeter of surface area

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Alligator Cracking

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Block Cracking

Block crack divide the asphalt surface intoapproximately rectangular pieces. The blocksrange in size from approximately 1 to 100 ft2.

Block cracking is caused mainly by the shrinkageof hot mix asphalt and daily temperature cycling.It is not load associated, although loads canincrease the severity of the cracks.

The occurrence of block cracking usually indicatesthat the asphalt has hardened significantly.

Block cracking is measured in square feet orsquare meters of surface area.

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Joint Reflection Cracking from Concrete Slab• This distress occurs only on pavements that have an asphalt

surface over a jointed concrete slab.• Cracks occur at transverse joints as well as at the

longitudinal joints where the old concrete pavement hasbeen widened before overlay.

• Joint reflection cracking is caused mainly by the movementof concrete slab beneath the asphalt surface because ofthermal or moisture changes and is generally not loadinitiated.

• However, traffic loading may cause a breakdown of the hotmix asphalt near the initial crack, resulting in spalling.

• Knowledge of slab dimensions beneath the asphalt surfacewill help to identify these cracks. Joint reflection cracking ismeasured in linear feet or linear meters.

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Longitudinal and transverse Cracking• Longitudinal cracks are parallel to the pavement

centerline, which transverse cracks extend across the centerline.

• They may be caused by the shrinkage of asphalt surface due to low temperatures or asphalt hardening or result from reflective cracks caused by cracks beneath the asphalt surface, including cracks in concrete slabs but not at the joints.

• Longitudinal cracks may also be caused by a poorly constructed paving lane joint. These types of cracks are not usually load associated.

• Longitudinal and transverse cracks are measured in linear feet or linear meters.

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Longitudinal Cracking

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Transverse Cracking

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Pumping and Water Bleeding

• Pumping is the ejection of water and fine materials under pressure through cracks under moving loads.

• As the water is ejected, it carries fine materials, thus resulting in progressive material deterioration and loss of support.

• Surface staining or accumulation of material on the surface close to cracks is evidence of pumping.

• Water bleeding occurs where water seeps slowly out of cracks on the pavement surface.

• Pumping and water bleeding are measured by counting the number that exists.

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Rutting

• A rut is a surface depression in the wheel paths.Pavement uplift may occur along the sides of the rut.

• However, in many instances ruts are noticeable onlyafter a rainfall, when the wheel paths are filled withwater.

• Rutting stems from any of the pavement layers or thesubgrade, usually caused by the consolidation or lateralmovement of the materials, due to traffic loads.

• Rutting may be caused by inadequate compactionduring construction.

• Rutting is measured in square feet or square meters ofsurface area.

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Rutting

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Swell

• Swell is characterized by an upward bulge on thepavement surface.

• A swell may occur sharply over a small area or asa long gradual wave.

• A swell is usually caused by frost action in the subgrade or by swelling soils, but a swell can alsooccur on the surface of an asphalt overlay onconcrete pavement as a result of blowup in theconcrete slab.

• Swells are measured in square feet or squaremeters of surface area.

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• Distresses caused by deficiencies inconstruction, materials or maintenance;

• Bleeding: Bleeding is a film of bituminousmaterial on the pavement surface, whichcreates a shiny, glass-like, reflecting surfacethat usually becomes sticky.

• It is caused by high asphalt content or low airvoid content. Since the bleeding process is notreversible during cold months, asphalt willaccumulate on the surface and lower the skidresistance.

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• Corrugations: Corrugation is a form of plasticmovement typified by ripples across theasphalt surface. It occurs usually at bus stopswhere vehicles accelerate or decelerate and isthe result of shear action between thepavement surface and the base materials.

Depression

• Depressions are localized pavement surfaceareas having elevations slightly lower thanthose of the surrounding pavement.

• They can be caused by the settlement offoundation soil during construction

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Patch deterioration

Deteriorations occur in a patch, which is an areawhere the original pavement has beenremoved and replaced with either similar ordifferent material.

• Traffic load, material, or poor constructionpractices can all cause patch deterioration

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Patching

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• Polished aggregates

• A portion of the aggregates extending abovethe asphalt surface is either very small orwithout rough or angular particles to providegood skid resistance.

• This type of distress occurs mainly in thewheel path due to repeated traffic loads.

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• Potholes

• Potholes are bowl-shaped holes of varioussizes on the pavement surface.

• They are caused by the broken pavementsurface due to alligator cracking, localizeddisintegration or freeze-thaw cycles.

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Concrete Pavements

• It is helpful to separate various defects commonto concrete pavements. Some defects arelocalized while others indicate that problems maydevelop throughout the pavement.

• Surface defects• Wear and polishing, map cracking, pop-outs,

scaling, shallow reinforcing, spalling.

• Joints• Longitudinal joint, transverse joints3/19/2013 25

• Pavement cracks

• Transverse slab cracks, D-cracking, cornercracks,

• Pavement deformation

• Blow ups; faulting; pavement settlement orheave; utility repairs, patches and potholes;manhole and inlet cracking.

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Wear and polishing:

• A worn or polished surface may appear from traffic wearing off the surface mortar and skid resistant texture.

• Sometimes traffic may polish aggregates smooth, causing the surface to be slippery.

• An asphalt overlay can restore skid resistance and remove ruts.

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Map cracking:

• A pattern of fine cracks usually spaced within severalinches is called map cracking.

• It usually develops into square or other geometricalpatterns. Can be caused by improper curing.

Pop-outs

• Individual pieces of large aggregate may pop out of thesurface.

• This is often caused by absorbent aggregates thatdeteriorate under freeze-thaw conditions.

• Surface patching can be done temporarily withasphalt.

•

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Scaling

• Scaling is surface deterioration that causes loss of fine aggregate and mortar.

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Shallow reinforcing

• If the steel reinforcing bar or mesh is placed too close to theconcrete surface it will lead to concrete spalling. Corrosion ofthe steel creates forces that break and dislodge the concrete.Often you can see rust stains in the surface cracks beforespalling occurs. Can be temporarily patched with asphalt

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Spalling:

• Spalling is the loss of a piece of the concretepavement from the surface or along the edgesof cracks and joints.

• Cracking or freeze-thaw action may break theconcrete loose, or spalling may be caused bypoor quality materials. Spalling may be limitedto small pieces in isolated areas or be quitedeep and extensive. Repair will depend on thecause. Small spalled areas are often patched.

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Spalling

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Longitudinal joints:

• Longitudinal paving joints are constructed tobe narrow in width and usually well sealed.

• As pavements age and materials deteriorate,joints may open and further deteriorate.

• Settlement, instability, or pumping of thesubgrade soil can cause longitudinal joints tofault

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Longitudinal joint

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Transverse joints• Transverse joints are constructed in concrete

pavements to permit movement of the concreteslabs.

• Some joints are constructed with load transferdowels. If the pavement has poor subsurfacedrainage, traffic may eventually create voidsunder the joints due to pumping and cause theslabs to settle or fault. Freeze-thaw deteriorationat the joint can cause

• spalling and create additional cracks parallel tothe joint. Load transfer bars may corrode,creating expansive forces that further deterioratethe concrete at the joint.

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Transverse joints

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Transverse slab cracks:

• Transverse cracks may appear parallel to joints and can becaused by thermal stresses, poor subgrade support, or heavyloadings. They are sometimes related to slabs having jointsspaced too widely.

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D-cracks

• Occasionally, severe deterioration maydevelop from poor quality aggregate.

• So called D-cracking develops when theaggregate is able to absorb moisture.

• This causes the aggregate to break apartunder freeze-thaw action which leads todeterioration. Usually, it starts at the bottomof the slab and moves upward.

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D- cracks

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Corner cracks:

• Diagonal cracks near the corner of a concreteslab may develop, forming a triangle with alongitudinal and transverse joint. Usuallythese cracks are within one foot of the cornerof the slab.

• They are caused by insufficient soil support orconcentrated stress due to temperaturerelated slab movement. The corner breaksunder traffic loading. They may begin ashairline cracks.

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Corner cracks

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Blowups

• Concrete slabs may push up or be crushed at atransverse joint. This is caused by expansion ofthe concrete where incompressible materials(sand, etc.) have infiltrated into poorly sealedjoints.

• As a result, there is no space to accommodateexpansion

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Faulting

• Joints and cracks may fault or develop a stepbetween adjacent slabs.

• Faulting is caused by pumping of subgradesoils and creation of voids.

• Heavy truck or bus traffic can rapidlyaccelerate faulting.

• Longitudinal joints may fault due tosettlement of an adjacent slab

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Faulting

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Utility repairs, patches and potholes:

• Replacement or repair of utilities will require cuts or utilityopenings. When repaired these pavement patches may showsettlement, joint deterioration, or distress under continuedtraffic loading.

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Manhole and inlet cracks:

• Normal pavement movement due to frostheaving and movements due to changes intemperature often cannot be accommodatedin the pavement adjacent to a manhole or astorm sewer inlet.

• Cracks and faulting may develop and theconcrete slab may deteriorate further.

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Transportation II ch6 2013

1 Prem N. Bastola

Road construction technology

Is the branch of highway engineering which deals with all kinds of activities and technology or operations for

changing the existing ground to the designed shape, slope. It provides all the necessary facilities for smooth, safe

and efficient traffic operation. It also includes the reconstruction of existing roads. The type of technology

depends upon the available resources which are available equipment, plant and human resources.

Various activities can be divided into

1. Earthwork

Site clearance, earthwork in filling for embankment

Excavation for cutting

Excavation for borrow pit

Excavation for structural foundation

Disposal of surplus earth

2. Drainage works

Side drains, Culverts, Sub- surface drainage, Causeways, Minor bridges, Other water management

structures

3. Structural works

Earth retaining structures, Gully control works, Landslide stabilization works, River training works

Bridge protection works. Anchor walls

4. Pavement works

Sub-grade preparation, Sub base preparation, Wearing course

5. miscellaneous works

Road furniture, Traffic sing, marking signal, Bio engineering

Tools, equipments and plants used in road construction

Since road construction done manually takes lots of time and it is difficult to achieve required degree of quality,

construction equipments are extensively used. For small works labour force may be more effective, but for large

projects construction equipments are most.

Tool



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Hand shovel, chisel, spade, hand hammer, brushes, trowel, wheel barrow

Equipments

1 Earth moving equipments

Dozer, Scraper, Loader, Excavator, Backhoe, Dragline, Clamshell, Trench digger

2 compaction

Smooth wheel roller, Vibrating roller, Pneumatic roller, Sheep foot roller, Rammers of various capacities

3 leveling equipment

Motor grader

4. Paving

Binder storage tank with heating device, Binder spreader/distributor, Aggregate spreader, Cement concrete

mixture, Bituminous paver, Concrete paver

5 lifting

Backhoe, Crane

6 transporting

Dumping trucks, Trucks flat body, Mini dumpers

7 miscellaneous equipments

Rock driller, Water tanker, Drilling machines, Blasting equipmetnes

Plant

Cement concrete plant, Asphalt concrete plant, Cold mix plant, Aggregate crushing plant, Screening plant,

washing plant, Sand blowing unit

Earthwork

The process of preparing the sub-grade to maintain level, designed grade by compaction is termed as earthwork.

It can be either filling or excavation depending on the nature of original ground and finalized section of the road.

It is economical to plan the movement of earth from cuts to the nearest fill and so on.

Planning of Earthwork



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Planning of earth movement during earthwork in road construction is important and essential for efficient usage

and minimizing the cost. Highway construction involves a large amount of earthwork in cut and fill. Planning is

best done by drawing mass haul diagram.

Mass haul diagram-

A graphical representation of the cumulative amount of earthwork moved along the centerline and distances over

which the earth and materials are to be transported after correction due to soil condition

Is the graphical representation of the amount of earthwork involved in road construction and the manner in which

may be most economically handled. Each ordinate in the diagram is the balance of materials obtained form cut

and used in fill.

Shrinkage or swell factor: It is well known that one cubic meter of excavation on amount will not occupies

exactly 1 m3

of space in the fill, so adjusting is required. This can be done by using the shrinkage or swell

factor.

- Borrow: It is the location away from the Right of Way (R.O.W.) and it is chosen by the Engineer. The borrow

pits soil should be comply with the followed specification (preferably out of R.O.W.).

Note: there is a problem in urban areas because of borrow cost.

- Waste: It is the unwanted excavation material which should be disposed out of R.O.W.

Vertical Axis- Cubic Yards/meter (excavation and embankment).

Horizontal Axis- Stationing

Characteristics of Mass Curve:

1- Rising sections of the mass curve indicates areas where excavating exceeds fill, whereas falling sections

indicate where fill exceeds excavation.



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2- Steep slopes reflect heavy cuts & Fills, while flat slopes indicate areas fro small amount of earthwork.

3- The difference in ordinates between any two points indicate net excess of excavation over embankment or

vise versa.

4- Any horizontal line dawn to intersect two points within the same curve indicates a balance of excavation

(cut) and embankment (fill) quantities between the two points.

5- Points of zero slope represent points where roadway goes from cut to fill or from fill to cut.

6- The highest or the lowest points of the mass haul diagram represents the crossing points between the grade

line (roadway level) and natural ground level.

Mass diagrams determine the average haul, free haul, and overhaul on a given segment of roadway.

Mass diagrams tell the contractors and inspectors the quantity of material moved and how far it can be

economically moved.

Haul- it is the distance over which the material is moved.

Free haul- is the distance to which the contractor is supposed to move the earth without any additional charges.

Overhaul- is the distance in excess of free haul for which the contractor will be paid extra for each unit of

haulage

Economic haul- when the haul distances are large it may be more economical to waste excavation material and

borrow from a more convenient source than pay for overhauling.

Site clearance

It is the first operation after the completion of survey works for fixing the road alignment. Some works included

are- clearing grass, weeds, bushes, shrubs and top organic soil at least covering toe width

Removal of trees, stumps, and roots along the alignment up to right of way

Removal of existing structures along the alignment

Embankment for filling

When it becomes necessary to raise the sub-grade of a road above the existing ground level embankments are

constructed. Raising of sub grade may be due to – water table, to prevent pavement due to surface and capillary

water

To maintain the design standards wrt vertical alignment.

Various elements of embankment are

Height, fill material, settlement, stability of foundation and slopes



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Excavation for cutting

Is the process of cutting and removing the earth including rock form its original position. The cut material is

transported and dumped as a fill or spoil bank. Depending on the nature of soil or rock cutting equipments are

selected.

Elements are – depth, stability of foundation, slopes, accommodation of side drains

Pavement construction:-

for definition and types of pavement refer ch 5

Types of pavement construction

ü earthen road

ü gravel road

ü water bound macadam[WBM]

ü soil stabilized roads- mechanical stabilization, soil cement stabilization, soil lime stabilization, soil

bitumen stabilization

ü bituminous/ black topped roads- prime coat, tack coat, surface dressing, otta seal, grouted/penetration

macadam

ü premixes- BBM bituminous bound macadam, bituminous carpet, asphalt concrete, mastic asphalt

ü cement concrete roads- cement grouted layers, rolled concrete layers, cement concrete slabs

Before the construction of pavement layers, sub-grade is prepared [refer earthwork page3]. The site should be

cleared off and grading is done to bring the vertical profile to meet the design standards. It is essential to compact

the top of formation adequately starting from edge to the centre on straight section and from inner edge to outer

edge where super elevation exists.

Earthen road

it is the cheapest type of road. General camber is 4 to 5%. Steep camber is preferred for quick removal of water.

Equipment- grader, roller, tipper and water tanker or manually for small projects

Procedure-

Soil survey- beyond the right of way, extracted material from borrow pit should be free from organic matter

Centre line and reference points are fixed with wooden pegs

Prepare the sub-grade as stated earlier



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The borrow soil [if necessary mix different types of soils to desired proportion] is dumped on the prepared sub-

grade and pulverized. The field moisture condition is checked and water added if needed to bring the moisture

content to OMC.

Spread the soil over the carriage way and rolled in compacted thickness

Open to the traffic after setting of compaction

For quality control- conduct Atternberg limit and proctor density test

Check for camber

Check filed moisture density and dry density [ minimum 95%]

Gravel road

Superior to earthen road, carry heavier traffic, normal camber 3 to 4%.

Two types of construction- feather type and trench type

Material- clean, hard, strong, tough, durable varieties of crushed stones or gravel of specified gradation. Rounded

and river gravel is not preferred as they have poor interlocking. CBR>60%

Equipment- as above

Procedure-

Gravel is stacked along the sides of proposed road

Wooden pegs fro centre line and reference points are marked

Preparation of sub-grade- as above

Placing of gravel as per types of construction

Spread with greater thickness at centre and less towards the edges to obtain desired camber

Compaction with smooth wheel roller or vibratory roller. Half width of roller overlapping during compaction

Open to traffic after completion

For quality- as above [ density >98%

Water bound Macadam [WBM]

Is known after the name of John Macadam. The main principle is- crushed or broken stone aggregates are bound

together by the action of rolling or traffic compaction. The binding is achieved by using stone dust as filler



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material in presence of water. Usually thickness is 8 to 30cm with compaction done on thickness of 8 to 15 cm as

one layer. Normal camber 2.5 to 3.5%

Material- WBM roads with gravel including crushed gravel, hard broken stones or soft broken stone with brick

ballast, blast furnace slag etc

Coarse material, screening material and stone dust are required. Clean, hard, strong durable and free from excess

of flaky, elongated or soft and dirt. LAAV =max 40%

Grading Size range Screening size

1 90 to 40 mm 12.5mm

2 63 to 40 mm 10mm

3 50 to 25mm 10mm

Equipment- aggregate spreader, roller, tipper, water tanker

Procedure-

Preparation of sub-grad as mentioned above

Materials with compaction factor [nearly 20 % extra] are stacked along the road

Arrangement of lateral confinement

Spreading of coarse aggregates with compacted thickness of 8 to 15 cm

Compaction with smooth wheel roller of 6 to 10 tonnes

Application of screening aggregates and wet rolling to fill about 50% voids

Application of filler materials with PI≤9% in tow thin layers

Finishing of the surface with 6cm sand sprinkling water and rolled

Making of shoulders

Open to traffic after few days of completion

For quality- LAAV, CBR others as above

Soil stabilized roads

Due to financial limitations developing countries are compelled to strengthen their road network by stage

construction. The construction cost can be dramatically lowered by selecting local materials. If the stability of the

soil is not adequate to support the wheel loads soil properties are improved by soil stabilization methods. The

main principle is the effective use of local soil and other material suitable stabilizing agents with low cost.



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Mechanics of soil stabilization

It is the improvement of stability or bearing capacity of the soil by using controlled compaction, proportioning

and addition of suitable admixture. It deals with physical and chemical methods to make stabilized soil serve as a

pavement component.

Evaluate the properties of available soil, decide the method of stabilization, and design the stabilized mix,

adequate compaction.

Techniques of soil stabilization

Proportioning- locally available soils and aggregate mixed in suitable proportion

Cement agents- adding Portland cement, lime, bituminous materials

Modifying agent- Portland cement, lime for highly clayey soil

Water proofing agents- bituminous materials

Water repelling agents- organic compounds [resinous materials]

Water retaining agents- calcium chloride for non-cohesive soil

Heat treatment- heat treated soil

Chemicals- several chemicals <0.5% by weight of soil

In all the above technique adequate compaction is a must

Methods- as stated in page 3

Mechanical soil stabilization-

Basic principle- proportioning and compaction

Material- LL<25%, PI<6

Equipment- as above

Procedure

Preparation of sub-grade

Mixing of materials to a desired proportion as per design

Checking of moisture content, and add water if desired

Spreading of mixed materials and compaction by roller



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Open to traffic after few days

For quality – as above [dry density min 95%]

Prime coat/ tack coat [For detail refer chapter 5 class handouts]

Prime coat is applied on relatively pervious layer such as crushed stone base and tack coat is applied on relatively

impervious layers such as existing bituminous layer with low viscosity cutback. The main function is to seal the

pores, water proof the underlying layers.

Material- either MC30 or MC 70 or bitumen emulsion

Equipment- mechanical broom or hand brushes, air compressor, bitumen storage tank with heating devices,

bitumen distributor, trays

Procedure

Preparation and intensive broom of underlying layer for better penetration of spread cutback

Spreading of cutback on the prepared surface at

Curing until the surface is dried

For quality- test cutback for suitability, temperature before application, and rate of application

Surface dressing

Most common and cost effective method used as wearing course. It provides a dust free surface, water proof

layer.

Three types of construction- SBSD [single bituminous surface dressing], DBSD, TBSD

Material- normally 80/100 straight run bitumen

Aggregate- LAAV max 35%, ACV max 30%, water absorption max 1%

Equipment- storage tank with bitumen heating device, mechanical broom, air compressor, bitumen distributor,

aggregate spreader, pneumatic roller

Procedure-

Preparation of existing surface by mechanical broom or whatsoever

Spreading of binder at specified rate

Spreading of stone chipping at certain rate as specified

Rolling with pneumatic roller at least four passes [SBSD]



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Opening to traffic with controlled speed < 10 kmph for one to two weeks

Broom and clean the loose chips


Spreading of stone chipping at certain rate as specified for second coat

Rolling with pneumatic roller at least four passes [DBSD]


Broom and clean the loose chips


Spreading of stone chipping at certain rate as specified for third coat

Rolling with pneumatic roller at least four passes [TBSD]


For quality control- check equipments, temp of binder, test of binder- penetration, viscosity, ductility etc, test of

aggregates such as LAAV, ACV, etc

Grouted/ penetration Macadam

Full grout- if the bitumen penetrates to full depth of semi grout- penetrates upto half the depth. Full grout is

adopted in places of high rainfall and semi grout in average rainfall areas and traffic. Normally 7.5cm thickness

for full grout and 5cm for semi grout.

Material- bitumen 80/100 grade

Aggregate- clean, strong, hard, durable with LAAV max 40%, aggregate impact value max 30%

Max size of aggregate- for full grout 63mm down coarse aggregate and key aggregate of 25mm down. For semi

grout coarse agg of 50mm down and key 20 mm down.

Equipment- as per surface dressing

Procedure-

Preparation of existing surface by broom

Spreading of coarse aggregate as per specification

Dry rolling of the coarse aggregate at least with 10 ton roller

Spreading of bitumen at rate specified



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Spreading of key aggregates as specified

Rolling key aggregate at least 10 ton roller

Application of seal coat

Open to traffic

For quality- as per surface dressing

Bituminous bound Macadam

Is a premix laid in finished thickness of 5 or 7.5cm. size of aggregate depends on thickness of layer and

maximum size limited to 37mm for 7.5cm. it is open graded premix used as base course. If used as wearing

course provide seal coat.

Material- as above

Equipment- as above

Procedure-

Preparation of existing surface by broom

Application of prime coat/tack coat

Production of hot mix in plant or trays

Spreading of mix with mechanical paver or manually

Rolling of the mix laid with 10 ton roller

Application of seal coat

Open to traffic

For quality- as above

Cement concrete pavement

It is the construction of pavement over the sub-grade or prepared sub-base. Different types of construction are in

practice as discussed in chapter 5 [types of rigid pavement]. However these days cement concrete slabs are usual.

Material- OPC

Coarse aggregate- LAAV less than 35%, ACV and AIV <30%

Fine aggregate- free from deleterious material



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Equipment- concrete mixture, batching device, wheel barrow, needle vibrator, brushes, edging tools, concrete

paver etc

Procedure-

Preparation of sub-grade or sub- base

Placing of forms

Batching of ingredients and mixing

Transportation and placing of concrete

Compaction and finishing

Curing of concrete

Open to traffic

For quality- test of cement, test of cubes, curing by jute bags.

Further reading- highway engineering by Khanna & Justo p 409 to p 448



1 Prem N. Bastola

Highway maintenance

Maintenance is the series of interdependent activities carried out on and off the road surface with a view to

preserve the asset and to maintain its serviceability

It is the process carried out to preserve and keep the serviceable conditions of highwy as normal as possible. It

the maintenance works are not done at all or done faulty the useful life may drastically be reduced. It causes the

waste of huge investment of funds and effort of the project as a whole. Maintenance is an important activity

which helps in providing better service facilities, longer life and better appearance.

On poorly designed and constructed roads the cost of maintenance may be higher than the initial cost, hence

proper design and construction are very important.

Some common maintenance problems are

Drainage works, soil and geological conditions, directness of route, landslide problems

Importance of maintenance

All types of pavements require maintenance, though this is almost nill in case of rigid pavements. Maintenance

may be required because of stresses cased by the traffic, change in temperature and moisture conditions, and the

movement of embankment soil.

One may refer to various types of distresses in pavements as discussed in ch5, which require maintenance.

Like any other assets Road asset needs care and upkeep once it is constructed and put to use

Classification of maintenance activates

Depending on the types of failure and the remedial works the maintenance works can be

1. Road maintenance

2. Road side maintenance

Road maintenance involves works on the raod way [carriageway and shoulder] and on all structures within

and immediately adjacent to the roadway such as side drains, culverts, causeways, bridges.

Road side maintenance involves works on the structures and surfaces above and below the road having direct

active and passive influence on the road. This may be culverts, protection works,, retaining walls, catch

drains, cut slopes and fill slopes, river protection works

Road maintenance can be of following types

ü Routine maintenance- operations of localized nature require continuous works on any type of road

whatever its traffic volume be. The works are generally carried out by labour and can be contracted out.



2 Prem N. Bastola

It involves such activities as grass cutting, grading and reshaping of unpaved shoulders, clearing and

cleaning of side drains and culverts, road sign maintenance and repair of road side structures.

ü Recurrent – operations of localized nature and of limited extents can be carried out at more or less regular

interval of six months to two years depending on the need for frequency. The works are generally done

by using minor equipments. Activities for paved road can be – sealing of cracks, surface treatment, repair

of depressions, and ruts, pothole patching, edge repair etc

ü Preventive maintenance- maintenance operation of road surface, geological and geotechnical nature to

protect the roadway. The activities include – sealing of cracking, sealing of longitudinal and transverse

cracks, laying of net on slopes, trimming of loose material including stones on slopes, installation of

subsurface drainage, construction of retaining walls, cascade, check dam, river training etc.

ü Periodic maintenance- operations of large extent required only at intervals of several years, such as

resealing [ surface treatment], thin overlay

ü Emergency maintenance- urgent emergency works needed for reopening the road of constriction of

temporary diversion to allow the traffic to pass around the obstruction such as slides, road washouts.

Removal of debris, and other obstacles, placement of warning signs and diversion works

This also includes- maintaining the road after the critical period is over specially after the rainy season,

construction of new river training structures, and road side maintenance as required.

Maintenance- works performed to upkeep the pavement in its as constructed condition

Rehabilitation- measures improving the structural strength of pavement

Reconstruction- upgrading of road elements and partial change in horizontal and vertical alignment for better

route including strengthening of pavement

Purpose of Maintenance

�Reducing deterioration

�Lowering vehicle operating costs

�Keeping the road open

�Safety

�Environmental issues

Planning- Planned Maintenance is systematic and efficient application of Routine, Recurrent and periodic road

maintenance so as to preserve the road asset and provide desired level of service to the traveling public

Before selecting any type of maintenance aforementioned, it is advised to know the types of failure and damages

and its cause so that an appropriated and effective measure can be taken for maintenance. This saves time and

money required for maintenance. According to the degree of damage and available fund prioritization can be

made.

Types of failure and their causes—refer ch 5 [distress in pavement]



3 Prem N. Bastola

Pavement Condition evaluation

it is to assess the existing conditions of the road and make decision to what extent the pavement fulfills the

intended requirement

Methods of pavement evaluation

ü Structural evaluation – carrying capacity of road by Benkelman beam

ü Evaluation of pavement surface condition- finding SDI and RI( roughness index)

Pavement Deterioration Characteristics

�Road deteriorate over time

�Deterioration is progressive

�Deterioration is mainly due to;

�Environment

�Traffic

�Construction Methodology

Pavement condition considered “GOOD”

� Period of limited visible deterioration (minor cracking, occasional potholes, edge damage)

�Good serviceability

�Marginal increase in roughness

Visual inspection

Survey and measurement of SDI

Measures of distress can be either subjective or objective.

‧ A simple example of a subjective measurement may be a rating of high, medium, or low based on a brief visual

inspection.

‧ Objective measurements, which are generally more expensive to obtain, use different types of automated

distress detection equipment.

‧ Walk over survey and visual inspection of 10-20 % of road section

Minor Defects

CN: Narrow Interconnect Cracks

CL: Line Cracks

M: Sealed Cracks/ Patch Work

RA: Shallow Ravelling or Scaving

S: Slickness / Bleeding

ES: Short Edge Break

Major Defects

CW: Wide Interconnected Cracks

V: Scabbing

RL: Rut Depth

P: Pot Hole

G: Exposed Base or Sub-Base or Gravel

EL: Long Edge Break

D: Corrugation



4 Prem N. Bastola

Condition and intervention level according to Surface Distress Index

Prioritization

It is carried out at regional level. Critical parameters associated are

ü Traffic group index [TGI]

ü Road condition index [RCI]

ü Strategic importance index [SI]

Index values developed for traffic, road condition, and strategic importance are based on the experience gained in

the past.

Ranking index = TG+ RC+ SI

Value of traffic index

Traffic volume veh/day

Low< 250 Medium 250 -1500 High>1500

TG 0.15 0.5 0.9

RCI



5 Prem N. Bastola

Surface distress index [SDI]

0 to 0.17 [good] 1.8 to 3 [fair] 3.1 to 5 [poor]

RC 0.02 0.3 1.0

SI

Low importance Medium high

SI 0 0.3 0.6

Types and methods of repair

Maintenance of low cost road

Usual damages caused in earthen road require frequent maintenance which are the formation of dust in dry

weather and formation of longitudinal and cross ruts along the wheel path. Remedial measures are

ü Frequent sprinkling of water, use of dust palliatives

ü Reshaping of the road way during and after monsoon

ü Surface treatment or provision of stabilized layer on the top

Maintenance of gravel and WBM

Usual damages of the surfaces are due to fast moving vehicles. Due to formation of dust during dry and mud

formation in rainy seasons binding material get loose and deteriorate thus deleloping ruts and potholes. Remedial

measures are

ü Spreading of thin layer of moist soil binder after monsoon

ü Use of dust palliatives

ü Providing a bituminous surface dressing over WBM

ü Patch repair and rut and potholes repair

ü Resurfacing after useful life

Maintenance of bituminous roads

Depending on types of failures remedial measures can be taken for pavement surface and shoulder distress

ü Patch repair

ü Pot holes repair

ü Surface treatment

ü Slurry sealing

ü Repair of depression and shoulder

ü Repair of pavement edge

ü Resurfacing

Maintenance of concrete roads



6 Prem N. Bastola

Few maintenance works are required for concrete pavements. Formation of cracks are most common [see stress

calculation in rigid pavement]

ü Sealing of cracks from ingress of water- dirt, sand and other loose materials are removed, cleaned.

Kerosene is applied for better bond. The cracks are then filled with suitable bituminous sealing

ü Investigation of type of failure and overlay can be applied [ see types of overlay]

ü Maintenance of joints- these are the weakest part in such pavement, in summer expansion and in winter

contraction- joints get open and cracks are formed – which require sealing.

Overlay

As the highways age and deteriorate, some types of treatment is eventually required to provide a safe and

serviceable facility for the users. The types of treatments can range from simple maintenance to complete

reconstruction, depending on the circumstances. For pavements subjected to moderate and heavy traffic, the most

prevalent treatment is to place an overlay on the existing pavement.

Types of overlay

HMA overlays on asphalt pavements

HMA overlays on PCC pavements

PCC overlays on asphalt pavements

PCC overlays on PCC pavements

Overlay design for flexible pavements

Principles of design

An overlay design differs from the design of a new pavement. The strength of the existing pavement is to be

evaluated, whereas in the later, the strength of the sub-grade on which the new pavement has to be constructed is

evaluated. Thus, overlay designs involve the following steps;

ü Estimation of the traffic to be carried by the overlaid pavement

ü Measurements and estimation of the strength of the existing pavement

ü Determination of the thickness and type of the overlay..

Measurement of pavement strength

The measurement of deflection of a flexible pavement is one of the indirect methods for assessing its strength.

Most of the methods currently in use by various organizations around the world use deflection criterion as the

basis of design. The ease and speed with which deflection can be measured without disturbing the pavement

structure.

IRC guidelines



7 Prem N. Bastola

The IRC have formulated guidelines for design of overlays on flexible pavements. The method is based on

measurement of pavement deflection by the Benkelman beam.

Principle

A well compacted pavement section or one which has been well conditioned by traffic deforms elastically under

each wheel load application such that when the load moves away, there is an elastic recovery or rebound

deflection of the deformed pavement surface.

Procedure

1. The stretch of road length to be evaluated is first surveyed to assess the general condition of the

pavement with respect to the ruts, cracks and undulations.

2. The pavement stretches are classified and grouped into different classes (of length not less than 500m)

such as good, fair and poor for the Benkelman Beam studies.

3. The loading points on the pavement for deflection measurements are located along the wheel paths, on a

line 0.9m from the pavement edge in the case of pavements of total width more than 3.5m; the distance

from the edge is reduced to 0.6m on narrow pavements.

4. A minimum of 10 deflection observations may be taken on each of the selected stretch of pavement.

5. The truck is driven slowly parallel to the edge and stopped such that the left side rear duel wheel is

centrally placed over the first point for deflection measurement.

6. The probe end of the Benkelman beam is inserted between the gap of the dual wheel and is placed

exactly over the deflection observation point.

7. The initial dial gauge reading D0 is noted.

8. The truck is moved slowly through a distance of 2.7m from the point and stopped. The intermediate dial

gauge reading Di is noted.

9. The truck is then driven forward through a further distance of 9.0m and the final dial gauge reading Df is

recorded.

10. The three dial gauge reading D0 ,Di, and Df form a set of readings at one deflection point under

consideration. The deflection observations are continued at all the desired points.

11. The rebound deflection value D at any point is given by one of the following two conditions;

a) D=0.02(D0-Df) mm , If Di-Df < 0.025mm

b) D=0.02(D0-Df) + 0.02K(Di-Df)mm if Di-Df > 0.025mm

The value of K is to be determined for every make of the beam and generally this value of

Benkelman Beam in India is found to be 2.91.

12. The mean value of the deflections at n points is given by

� � =∑ �

� � �

The standard deviation of the deflection values is given by;



8 Prem N. Bastola

� = �∑(� � − � )�

(� − 1)

∆ � = � � + 2�

Correction for pavement temperature and subgrade moisture variation

The IRC suggested a standard pavement temperature of 350C and a correction factor of 0.0065 mm per 0C to be

applied for the variation from this standard pavement temperature. The correction will be negative when the

pavement temperature of is above 350C and positive when it is lower. However it is suggested that deflection

studies should be carried out when the pavement temperature is above 300C, if this correction factor is to be

applied.

IRC has suggested that tentative correction factor of 2.0 for clayey soil and 1.2 to 1.3 for sandy subgrade soils

may be adopted if the deflection observations made during dry seasons.

Allowable deflection as per IRC guidelines given in table

Design traffic (com.veh/day) Allowable deflection, mm

150 – 450

450 – 1500

1500 - 4500

1.5

1.25

1.00

If the characteristic deflection is greater than the allowable deflection, the thickness of the overlay is then

determined by the following formula.

= � � � �∆ �

∆

Where; h= Thickness of granular overlay (WBM) in mm

∆� = Characteristics deflection

∆ =allowable deflection

R=constant, whose value may be taken as 550

Benkelman Beam deflection studies were carried out on 15 selected points in mm are given-1.4, 1.32, 1.25, 1.35, 1.48, 1.6,

1.65, 1.55, 1.45, 1.40, 1.36, 1.46, 1.50, 1.52, 1.45 mm. If the present traffic consists of 750 commercial vehicles per day,

determine the thickness of bituminous concrete overlay required, if the pavement temperature during the test was 300C and

the correction factor for subsequent increase in subgrade moisture content is 1.3. Assume annual rate of growth of traffic as

7.5%.


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1

Introduction to Bridge and Tunnel Engineering

3/20/2013 1Prem N. Bastola

introduction

• A structure constructed over an obstacle to provide the passage

• Road bridge- movement of traffic

• See NRS 2045

• Cross drainage structure span greater than 6m

• In worst cases culverts can go up to 8m

3/20/2013 2

Characteristics of ideal bridge

• Line of bridge should be centered to the line of approach as far as possible

• It should be leveled

• Sufficient width

• Safe for standard load

• Adequate underway width and height

• Strong foundation

• Economical

3/20/2013 3

Ideal location

• Straight reach of river

• Steady regime of river

• Narrow and well defined channel

• Rocky and non erodible foundation

• no sharp curves in the approaches

• Easy construction- no excess works

• Least drainage works

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Factors affecting bridge type

• Strong enough• Sufficient • Economical• Aesthetic• Economy in overall construction • Span • Topography and soil condition • Funds available• Traffic types and intensity

3/20/2013 5

Classification

• According to span• Minor bridge- more than 6m span and upto 20m

in length• Medium- Span less than 20m and total length

above 20m• Major – span length greater than 20m• According to loading• Major bridge- IRC class AA loading• Medium- IRC class A• Temporary- IRC class B eg timber bridge

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2

• According to structure• RCC T or simply supported• Cantilever• Double cantilever• Arch • Suspension • Cable stayed• Steel• movable

3/20/2013 7

• Type of material

• Timber

• RCC

• Masonry

• Steel

• Floating eg boat

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Components parts

• Foundation for the abatements and piers or towers

• Abutment and piers

• River training works like revetment for slopes, aprons for bed u/s and d/s guide bunds

• Approaches to the bridge to connect the road

• Decking- girders or trusses or slabs

• Bearing for girders

• Handrails guard stones etc

3/20/2013 9

Hydraulic analysis

• Detailed study of characteristics of river beneath

• Information such as channel stability

• Sediment discharge

• Scour

• Sediment deposition

• Hydrodynamic forces

• Hydraulic data from survey

3/20/2013 10

Importance of hydraulic factors

• Geotechnical, hydraulic and structural combination

• The hydraulic parameters affecting bridge desing are

• Site reconnaissance

• Review and analysis of available water

• Hydraulic survey

• Maximum flood level

• Minimum flood level

3/20/2013 11

• Design flood

• Bed and bank characteristics

• Approach velocity and direction

• River meandering characteristics

• Normal scour depth

• Backwater effect

• Flow velocity

• Structural loading

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3

• Soil characteristics

• Economy of construction

• Availability of resources- manpower, machine and money

• Proper freeboard

• Vertical clearance and height

• Location and geometry of piers

• The cost of alternative scheme etc

3/20/2013 13

River training works

• River Bank and protection structures

• Provision of spur, guide bunds

• For detail- -see IRC guideline 89-1997

• Further reading- any text book on Irrigation and hydraulic structures

3/20/2013 14

Tunnel

• Road tunnels as defined by the AmericanAssociation of State Highway and TransportationOfficials (AASHTO) Technical Committee forTunnels (T-20)

• are enclosed roadways with vehicle access that isrestricted to portals regardless of type of thestructure or method of construction.

• The committee further defines road tunnels notto include enclosed roadway created by highwaybridges, railroad bridges or other bridges.

3/20/2013 15

• Road tunnels are feasible alternatives to cross awater body or traverse through physical barriers

• such as mountains, existing roadways, railroads,or facilities;

• or to satisfy environmental or ecologicalrequirements.

• In addition, road tunnels are viable means tominimize potential environmental impact such astraffic congestion, pedestrian movement, airquality, noise pollution, or visual intrusion;

3/20/2013 16

• to protect areas of special cultural or historicalvalue such as conservation of districts,buildings or private properties; or for othersustainability reasons such as to avoid theimpact on natural habit or reduce disturbanceto surface land

3/20/2013 17

• Planning for a road tunnel requires multi-disciplinary involvement and assessments

• should generally adopt the same standards as forsurface roads and bridge options, with someexceptions as will be discussed later.

• Certain considerations, such as lighting,ventilation, life safety, operation andmaintenance, etc should be addressed specificallyfor tunnels.

•

3/20/2013 18


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4

• In addition to the capital construction cost, a life cycle cost analysis should be performed taking into account the life expectancy of a tunnel.

• It should be noted that the life expectancies of tunnels are significantly longer than those of other facilities such as bridges or roads.

3/20/2013 19

Tunnel cross section

• There are three main shapes of highway tunnels • – circular, rectangular, and horseshoe or

curvilinear. • The shape of the tunnel is largely dependent on

the method used to construct the tunnel and on the ground conditions.

• For example, rectangular tunnels are often constructed by either the cut and cover method

• by the immersed method (Chapter 11)• or by jacked box tunneling (Chapter 12).

3/20/2013 20

• Circular tunnels are generally constructed byusing either tunnel boring machine (TBM)

• or by drill and blast in rock.

• Horseshoe configuration tunnels are generallyconstructed using drill and blast in rock or

• by following the Sequential ExcavationMethod (SEM), also as known as New AustrianTunneling Method (NATM)

3/20/2013 21

Elements

• A road tunnel cross section must be able toaccommodate the horizontal and vertical trafficclearances, as well as the other required elements. Thetypical cross section elements include:

• Travel lanes

• Shoulders

• Sidewalks/Curbs

• Tunnel drainage

• Tunnel ventilation

• Tunnel lighting

3/20/2013 22

• Tunnel utilities and power• Water supply pipes for firefighting• Cabinets for fire extinguishers• Signals and signs above roadway lanes• CCTV surveillance cameras• Emergency telephones• Communication antennae/equipment• Monitoring equipment of noxious emissions and

visibility• Emergency egress illuminated signs at low level

(so that they are visible in case of a fire or smokecondition+)

3/20/2013 23

Site Reconnaissance and Preliminary Surveys

• Initial on-site studies should start with a careful reconnaissance over the tunnel alignment,

• paying particular attention to the potential portal and shaft locations.

• Features identified on maps and air photos should be verified.

• Rock outcrops, often exposed in highway and railroad cuts, provide a source for information about r

3/20/2013 24


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5

• rock mass fracturing and bedding and the location of rock type boundaries, faults, dikes, and other geologic features.

• Features identified during the site reconnaissance should be photographed, documented and if feasible located by hand-held GPS equipment.

3/20/2013 25

• The tunnels are usually equipped with various systems such as

• ventilation,

• lighting,

• communication,

• fire-life safety,

• traffic operation and control including messaging,

• operation and control of the various systems in the tunnel.

3/20/2013 26

Classes of Roads and Vehicle Sizes

• A tunnel can be designed to accommodate any class of roads and any size of vehicles.

• The classes of highways are discussed in A Policy on Geometric Design of Highways and Streets Chapter 1, AASHTO (2004).

• Alignments, dimensions, and vehicle sizes are often determined by the responsible authority based on the classifications of the road (i.e. interstate, state, county or local roads).

• However, most regulations have been formulated on the basis of open roads.

• For example, the use of full width shoulders in the tunnel might result in high cost.

•3/20/2013 27

• Road tunnel A86 in Paris, for instance, is designed to accommodate two levels of passenger vehicles only and special low height emergency vehicles are provided

3/20/2013 28

3/20/2013 29

The design process

• Define the functional requirements, includingdesign life and durability requirements;

• Carry out the necessary investigations andanalyses of the geologic, geotechnical andgeohydrological data

• Conduct environmental, cultural, and institutionalstudies to assess how they impact the design andconstruction of the tunnel;

• Perform tunnel type studies to determine themost appropriate method of tunneling.

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6

• Establish design criteria and perform the design of thevarious tunnel elements.

• Appropriate initial and final ground support and liningsystems are critical for the tunnel design, consideringboth ground conditions and the proposed method ofconstruction.

• Perform the design in Preliminary and Final designphases.

• Interim reviews should be made if indicated byongoing design issues.

• Establish tunnel alignment, profile and cross-section

3/20/2013 31

• Determine potential modes of failure, includingconstruction events, unsatisfactory long-termperformance, and failure to meet environmentalrequirements.

• Obtain any necessary data and analyze these modes offailure;

• Perform risk analysis and identify mitigation measuresand implement those measures in the design

• Prepare project documents including constructionplans, specifications, schedules, estimates, andgeotechnical baseline report (GBR).

3/20/2013 32

• Planning. Maximum grade, horizontal and verticalcurves, and other requirement/constraints forroad tunnel horizontal and vertical alignments

• Road tunnel grades should be evaluated on thebasis of driver comfort while striving to reach apoint of economic balance between constructioncosts and operating and maintenance expenses.

• Maximum effective grades in main roadwaytunnels preferably should not exceed 4%;although grades up to 6% have been used wherenecessary

3/20/2013 33

• the curve radii should be as large as possibleand no less than 850 to 1000-ft radius. Atighter curve may be considered at thedetailed design stage based on the selectedtunneling method.

• Super elevation rate, which is the rise in theroadway surface elevation from the inside tothe outside edge of the road, shouldpreferably lie in the range 1% to 6%.

3/20/2013 34

Protection and safety

• Standard for Road Tunnels, Bridges, and OtherLimited Access Highways provides thefollowing fire protection and life safetyrequirements for road tunnels:

• Protection of Structural Elements

• Fire Detection

• Communication Systems

• Traffic Control

3/20/2013 35

• Fire Protection (i.e., standpipe, fire hydrants, water supply, portable fire extinguisher, fixed water-base fire-fighting systems, etc.)

• Tunnel Drainage System

• Emergency Egress

• Electric, and

• Emergency response plan.

3/20/2013 36


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7

Tunnel Drainage

• Good design anticipates drainage needs.• Usually sump-pump systems are provided at the

portals and at low points.• Roadway drainage throughout the tunnel using drain

inlets and drainage pipes should be provided.• The drainage system should be designed to deal with

surface drainage as well as any groundwater infiltrationinto the tunnel.

• Other areas of the tunnels, such as ventilation ductsand potential locations for leakage, should haveprovision for drainage.

• Accumulation of ice due to inadequate drainageprovisions must be avoided for safe passage.

3/20/2013 37

Lighting Requirements

• Lighting in tunnels assists the driver in identifying hazards• or disabled vehicles within the tunnel while at a sufficient

distance to safely react or stop.• High light levels (Portal light zone) are usually required at

the beginning of the tunnel during the daytime tocompensate for the "Black Hole Effect" that occurs by thetunnel structure shadowing the roadway

• These high light levels will be used only during daytime.• Tunnel light fixtures are usually located in the ceiling, or

mounted on the walls near the ceiling.• the location, size, type, and number of light fixtures impact

the geometrical requirements of the tunnel and should betaken into consideration

3/20/2013 38

Hole" (Left) and Proper Lighting (Right)

3/20/2013 39

Ventilation Requirements

• The ventilation system of a tunnel operates tomaintain acceptable air quality levels forshort-term exposure within the tunnel.

• The design may be driven either by fire/safetyconsiderations or by air quality

• which one governs depends upon manyfactors including traffic, size and length of thetunnel, and any special features such asunderground interchanges.

3/20/2013 40

• Ventilation requirements in a highway tunnelare determined using two primary criteria

• the handling of noxious emissions fromvehicles using the tunnel and

• the handling of smoke during a fire.

• Computational fluid dynamics (CFD) analysesare often used to establish an appropriatedesign for the ventilation under fireconditions.

3/20/2013 41

• An air quality analysis should also be conductedto determine whether air quality might governthe design.

• Air quality monitoring points in the tunnel shouldbe provided and the ventilation should beadjusted based on the traffic volume toaccommodate the required air quality.

• The two main ventilation system options used for tunnels

• longitudinal ventilation and transverse ventilation.

3/20/2013 42


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8

• A longitudinal ventilation system introduces air into, orremoves air from a road tunnel, with the longitudinal flowof traffic, at a limited number of points such as a ventilationshaft or a portal.

• It can be sub-classified as either using a jet fan system or acentral fan system with a high-velocity (Saccardo) nozzle.

• The use of jet fan based longitudinal system was approvedby the FHWA in 1995 based on the results of the MemorialTunnel Fire Ventilation Test Program (NCHRP, 2006).

• Generally, it includes a series of axial, high-velocity jet fansmounted at the ceiling level of the road tunnel to induce alongitudinal air-flow through the length of the tunnel

3/20/2013 43

• A transverse ventilation system can be either afull or semi-full transverse type.

• With full transverse ventilation, air supplyducts are located above, below or to the sideof the traffic tube and inject fresh air into thetunnel at regular intervals.

• Exhaust ducts are located above or to the sideof the traffic tube and remove air andcontaminants.

3/20/2013 44

• With semi-transverse ventilation, the supplyduct is eliminated with its "duties" taken overby the traffic opening.

• When supply or exhaust ducts are used, theflow is generated by fans grouped together inventilation buildings.

• Local noise standards generally would requirenoise attenuators at the fans or nozzles.

3/20/2013 45

Tunnel linings

• Tunnel linings are structural systems installedafter excavation

• to provide ground support,

• to maintain the tunnel opening,

• to limit the inflow of ground water,

• to support appurtenances and

• to provide a base for the final finishedexposed surface of the tunnel.

3/20/2013 46

• Tunnel linings can be used for initialstabilization of the excavation

• permanent ground support

• or a combination of both.

• The materials for tunnel linings covered inthis chapter are cast-in-place concrete lining

• precast segmental concrete lining

• steel plate linings and shotcrete lining

3/20/2013 47

• Road tunnels are often lined with concrete andinternal finish surfaces.

• Some rock tunnels are unlined except at theportals and in certain areas where the rock is lesscompetent.

• rock reinforcement is often needed.

• Rock reinforcement for initial support includesthe use of rock bolts with internal metal strapsand mine ties, un-tensioned steel dowels, ortensioned steel bolts.

3/20/2013 48


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9

• To prevent small fragments of rock fromspalling, wire mesh, shotcrete, or a thinconcrete lining may be used.

• Shotcrete, or sprayed concrete, is often usedas initial lining prior to installation of a finallining, or as a local solution to instabilities in arock tunnel.

3/20/2013 49

• Shotcrete can also be used as a final lining.

• It is typically placed in layers with welded wire fabric and/or with steel fibers as reinforcement.

• The inside surface can be finished smooth and often without the fibers.

• Precast segmental lining is primarily used in conjunction with a TBM in soft ground and sometimes in rock.

3/20/2013 50

• The segments are usually erected within the tail shield of the TBM.

• Segmental linings have been made of cast iron, steel and concrete.

• Presently however, all segmental linings are made of concrete.

• They are usually gasketed and bolted to prevent water penetration.

• Precast segmental linings are sometimes used as a temporary lining within which a cast in place final lining is placed, or as the final lining

3/20/2013 51

Methods of tunneling

• Tunnel constructed in soft material requiretemporary support by means of

• Suitably spaced bents of wood

• Steel with lagging

• Liner plates

• Forepoling/ spiling [see mining engineering]

3/20/2013 52

Tunneling in firm ground

• Traditional methods as drilling and blasting• Excavation by tunneling

• In traditional method- full face method• Suitable for comparatively firm soils where excavation

portion can hold itself for sufficient time to permitmucking

• The area to be excavated is divided into 3 sections.• The top section is cut and removed followed by similar

operations to section below• It is suitable for small size tunnel

3/20/2013 53

• Top heading and benching

• When excavated portion can not hold itself bythe time mucking and supporting operationsare carried out

• Heading is excavated and supported to the fulllength or part before benching is commenced

• The heading is always ahead of benching by aconvenient length

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10

• Drift method

• Suited for large size tunnel

• A pilot tunnel / drift is made in the side orcentre of the tunnel

• The drift is then widened by drilling holes onits faces

• Drift provides suitable arrangement forsupporting the excavation

3/20/2013 55

Tunneling in soft ground

• Tunneling with liner plate

• Suitable for medium soft ground

• Also for small drifts for running ground

• Liner plate is placed at the crown segment in apre-excavated cavity at top and two adjacentliner plates bolted on each side

• Plates are supported by props

• The arch section is gradually widened down

3/20/2013 56

• Needle beam method

• Full section of the tunnel is broken out

• The plates are set one by one

• Plates supported by radially set props/jacksfrom a centrally placed longitudinal girdercalled needle beam

3/20/2013 57

Shield method

• Suitable for tunneling tube railway in clay• Consists for circular shield of thick steel plates

with stiffeners• Operated manually or by machine• The shield is pushed forward into the excavation

by hydraulic jacks• The linings are circular in form• The cycle is- excavating and supporting the face,

advancing of shield and adding another ring to the permanent lining

3/20/2013 58

Tunneling in rock

• Tunnels are driven in rock by repeating in sequence the operation of drilling holes in the rock face

• Loading the holes with explosive, blasting

• Removing and disposing off the muck

• Full cross section may be excavated or one or more drift may be excavated

• Methods- full face, top heading and benching, drift method

3/20/2013 59

• Sequence of operation for construction of tunnel in rocky strata

• Marking tunnel profile• Setting up and drilling• Loading explosive and blasting• Removing foul gas• Checking misfire• Scaling• Mucking• Erecting support and lining

3/20/2013 60


1

Acronyms

DOR-Department of Roads

IRC-Indian Roads Congress

AASHTO-American Association of State Highway and Transportation

officials

HFL-Highest Flood Level


2

1.0 INTRODUCTION AND BACKGROUND

1.1 Department of Roads (DOR) has formulated these standards with a view to

establish a common procedure for design and construction of road bridges in

Nepal.

2.0 DEFINITION OF DIFFERENT TERMS

Afflux: A rise in water level behind the bridge structures due to obstruction to flow.

Bridge: A structure that spans a body of water, a valley, or a road and affords passage

for pedestrians, or vehicles of all kinds, or any combination thereof.

Design Discharge: That maximum discharge which the structure allows to pass through

it with fully serving its function.

Design Life: Period of time after construction throughout which the structure fulfills its

function for which it is constructed.

Footpaths: A portion of the bridge deck intended for the movement of pedestrian traffic

which is usually separated from vehicular movement by raising or by safety curb.

Free board: A vertical clearance of the lowest point of superstructure from the highest

flood level.

HFL: Level of the highest flood ever recorded or the calculated level for the highest

possible flood of specified return period.

Curb: The edge of a sidewalk next to the main roadway. The wheel-guard in a bridge.

Permanent Bridge: A bridge intended to provide a reliable passage of vehicles across a

river or any obstacles without interruption throughout its design life in contrary to

Temporary Bridges such as submergible causeways, ferries etc.

Return period: Also known as a recurrence interval is an estimate of the interval of time

between flood or river discharge flow of a design intensity or size.

Raised Curb: A curb that is raised above the level of the carriageway.

Safety Curb: A curb that separates vehicular movement from pedestrian movement with

a barrier.

Temporary Bridge: A bridge constructed to provide passage of vehicles either for

relatively a short period of a few years or few months or low level structures like

submergible/vented causeways or pontoons functioning during the period of low

discharge only.

3.0 GERNERAL

3.1 DESIGN LIFE

All permanent bridges shall be designed for a design life of minimum 50 years. Traffic

projections shall be made for a period of 30 years.


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3.2 DESIGN DISCHARGE

All permanent bridges shall be designed for a discharge of 100 yrs. return period. For

the calculation of design discharge empirical formulas especially developed for other

catchments shall not be used.

4.0 BRIDGE LOADINGS

4.1 ROAD BRIDGE LOADINGS

All permanent road bridges in Nepal shall be designed as per IRC loadings or AASHTO

loadings. All design shall be carried out in accordance to IRC standards for bridges

unless otherwise specified in this document.

5.0 GEOMETRIC STANDARDS

5.1 CARRIAGEWAY

• All bridges in Highways and Urban Roads shall be designed with a

minimum carriageway width of 7.5m.

• All bridges in Feeder Roads shall be designed with a minimum

carriageway width of 6.0m.

• No permanent bridge shall be designed with a carriageway width of less

than 6.0m except on minor (district and village) roads having length less

than 25m.

5.2 FOOTPATH

Footpaths shall be provided on all bridges located at settlement areas or on areas of

high movement of pedestrian traffic. They should be separated from the vehicular traffic

by safety curbs (in rural areas) and by raised footpath or curbs (in urban areas).The

width of the footpath should be decided according to projection of pedestrian traffic,

however, a minimum clear width(excluding the width of railings) of 1.0 m footpaths to be

provided, where necessary.

6.0 CLEARANCES

6.1 VERTICAL CLEARANCE

The vertical clearance is shown in Fig 6.1.

The vertical clearance of structures shall be,

I. For all roads not less than 4.75 m for through structures

II. Overhead wires, poles etc shall be at least 7.0 m above the highest point of the road surface.

6.2 HORIZONTAL OR LATERAL CLEARANCE

The horizontal clearance is the clear width available for the passage of vehicular traffic

as shown on Fig. 6.1.


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For culverts, the full roadway width as well as the width of shoulders shall be carried

through.

The size of curbs and footpaths shall be as shown in Fig. 6.1.

Fig. 6.1 Horizontal and Vertical Clearances

7.0 BRIDGE CLASSIFICATION

Classification of bridges shall be as follows:

� Culvert : Length up to 6 m

� Minor Bridge : When length ≤ 50 m (with span ≤ 25 m )

� Major Bridge : When span >25 m or length >50 m(with smaller spans)

� Special Bridge : Bridges that require special design considerations, whose construction features(e.g. concrete girder bridges with >50m span, steel trusses > 100m span, arch bridges, suspension bridges, cable-stayed bridges and other non-standard bridges).


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8.0 FREE BOARD

8.1 MINIMUM FREE BOARD

In case of bridges over water bodies, the free board from the design HFL with afflux to

the lowest point of bridge superstructure shall not be less than 1.0 m. The minimum

freeboard shall be as shown on the following table.

Table 8.1

Discharge m3/sec

Minimum Free board, mm

Less than 200 1000

201-500 1200

501-2000 1500

2001-5000 2000

5000 and above More than 2000 (depending on the reliability of the available data for the calculation of discharge)

9.0 CURBS AND SAFETY CURBS (BRIDGE BARRIERS)

Raised curbs shall not be less than 450 mm wide. Wider curbs shall be designed for

footway loadings. Height of raised curbs shall not be less than 200 mm.

The height of the safety bridge curb above the carriageway shall not be less than 500

mm from the safety consideration.

10.0 CARRIAGEWAY DRAINAGE

Transverse and longitudinal drainage of the carriageway shall be managed respectively

by providing a suitable cross fall and a camber or gradient. Water flowing down grade on

the approach should be intercepted and not permitted to run to the bridge.

The details of deck drains shall be such as to prevent the discharge of drainage water

against any portion of the structure and to prevent erosion adjacent to the outlet of the

drainage. Overhanging portion of concrete deck shall be provided with drip head or

notch, continuous where possible.

11.0 RAILINGS

Railings shall be provided along the edges of structures for protection of traffic and

pedestrians.

The height of the railing should be a minimum of 1.0 m from the top of the footpath or

curb surface.

12.0 MATERIAL SPECIFICATION

Material Specification is to be adopted as per Standard Specification for Road and

Bridges Works published by Ministry of Physical Planning and Works, Department of

Roads-2001.

13.0 PROVISION FOR UTILITIES

All bridges shall be designed taking into consideration the provision of carrying

utilities(electricity, water, telephone, cables etc.) through them wherever required.


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