Traffic studies (transportation engineering)

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TRAFFIC STUDIES
Transportation Engineering
(CE-421)

Traffic Studies
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Traffic studies are carried out to analyze the traffic characteristics.
These studies helps in deciding the geometric design features,
traffic control for safe and efficient traffic movement.
The various traffic survey studies generally carried out are;
 Traffic volume study
 Speed study
 Spot speed study
 Speed and delay study
 Origin and destination study
 Traffic flow characteristics
 Traffic capacity study
 Parking study
 Accident studies

Traffic Volume Study
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It is the number of vehicles crossing a section of road per unit
time at any selected period.
It is used as a quantity measure of flow: the commonly
units are vehicles/day or vehicles/hour
Object and Uses of Traffic Volume Study:
 It is generally accepted as a true measure of the relative
importance of roads and in deciding the priority for
improvement and expansion.
 It is used in planning, traffic operation and control of existing
facilities and also for planning the new facilities.
 It is used in the analysis of traffic patterns and trends.
 Useful in structural design of pavement
 Pedestrian traffic volume study is used for planning side walk,
cross walks, subway and pedestrian signals.

Main Methods of Volume Counting
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Automatic Counting Method
1. Direct Method
2. Indirect Method
Manual Counting Method
1. Contact System
2. Contactless System

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Manual counts are typically used to gather data for determination
of vehicle classification, turning movements, direction of travel,
pedestrian movements, or vehicle occupancy. Most applications of
manual counts require small samples of data at any given location.
The manually method is the method in which a
group of peoples are trained to record the total
numbers of vehicles crossing a section of the
road in desired period of time on record sheets
manually.

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Manual counts are sometimes used when the effort and
expense of automated equipment are not justified.
Manual counts are necessary when automatic equipment
is not available. Manual counts are typically used for
periods of less than a day. Normal intervals for a manual
count are 5, 10, or 15 minutes. Traffic counts during a
Monday morning rush hour and a Friday evening rush
hour may show exceptionally high volumes and are not
normally used in analysis; therefore, counts are usually
conducted on a Tuesday, Wednesday, or Thursday.

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Employs a field team to count and classify traffic volume.
Procedure
No. of observers required depends upon no. of Lanes and
type of information required.
More desirable to record traffic in each direction of travel
by posting separate observers for each direction.
For all-day counts ,work in three shifts can be arranged.
Data is recorded by Five- dash system. (IIII)

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Equipment for manual counts
Watch / Counter
clip board
Pencil, rubber, sharpner
Data sheet

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Manual Counting Method-Advantages
 Details such as vehicle classification and no. of occupants can
be obtained.
 Turning movement data of vehicles at intersections.
 Analyzing traffic characteristics in unusual conditions such as
adverse weather conditions, traffic breakdowns, temporary
closure of any lane of highway etc.
 Comparatively cheaper method of counting.
 Data accumulated by manual methods are easy to analyze.

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Manual Counting Method-Disadvantages
Not practicable to have manual count for 24 hrs of the
day and throughout the year.
Counts of remote areas is possible by automatic devices.

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An automatic survey involves placing a tube or loop across a road
which is connected to a box containing the means for storing the
information. In this method, vehicles are counted automatically
without any human involvement.
There are two techniques of automatic counting:
1. Contact system based on pneumatic, mechanical, magnetic
2. Contactless system based on electrical/optical, ultrasound /
infrared radar, micro-wave, CCTV/video image processing
method etc.

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 The automatic count method provides a means for gathering
large amounts of traffic data. Automatic counts are usually taken
in 1-hour intervals for each 24-hour period.
 The counts may extend for a week, month, or year. When the
counts are recorded for each 24-hour time period, the peak flow
period can be identified.
 Automatic counts are recorded using one of three methods:
portable counters, permanent counters, and videotape

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Portable Counters
Portable counting is a form of manual observation. Portable counters
serve the same purpose as manual counts but with automatic counting
equipment. The period of data collection using this method is usually
longer than when using manual counts. The portable counter method is
mainly used for 24-hour counts.
Pneumatic road tubes are used to conduct this method of automatic
counts Specific information pertaining to pneumatic road tubes can be
found in the users’ manual

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Permanent Counters
Permanent counters are used when long-term counts are to be
conducted. The counts could be performed every day for a year or
more. The data collected may be used to monitor and evaluate traffic
volumes and trends over a long period of time.
Videotape or Videography
Observers can record count data by videotaping traffic. Traffic
volumes can be counted by viewing videotapes recorded with a
camera at a collection site. A digital clock in the video image can
prove useful in noting time intervals.

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Pneumatic road tube
Pneumatic road tube sensors send a burst of air pressure along a rubber tube
when a vehicle's tires pass over the tube.

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Presentation Of Traffic Volume Data
 Traffic Flow Maps:
 Show volume along various routes by using bands
proportional to traffic volume carried.
 Thickness of lines represent traffic volume.
 Intersection Flow Diagrams
 Give direction and volume of traffic through an
intersection.
 Trend charts
 Shows the hourly , daily or monthly changes in volume
through an area.
 Useful for planning future expansion, design and
regulation

Traffic Studies
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SPEED STUDIES

Speed Studies
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Spot Speed
Instantaneous speed of a vehicle at a specified
location.
Average Speed
Average of the spot speeds of all vehicles passing a given
point on the highway.
Running Speed
Average speed maintained by a vehicle over a given
course while the vehicle is in motion.
Running speed= Length of course / Running time = Length of
course /( Journey time- Delays)

Speed Studies
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Journey speed
Also known as overall travel speed
It is the effective speed between two points. It is the distance
between two points divided by the total time taken by the
vehicle to complete the journey ,including all delays.
Journey speed = Distance/ Total journey Time (including
Delays)

Speed Studies
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Spot speed study
The speed at any spot is known as spot speed.
It may used for following aspects:
 Planning traffic control and regulation
 Geometric design
 Accident studies
 Traffic capacity
 Speed trends

Speed Studies
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 Works on the Doppler principle.
 Speed of a moving body is proportional to change in
frequency between the Radio wave transmitted to the moving body
and the radio wave received back.
 Instrument directly measures speed.
 Instrument is setup near the edge of carriageway at a height of
1m.
 The speed meter is so kept that the angle between
direction of travel of vehicle and axis of transmission of
radio wave is as low as possible, say within 20˚.
 Speed of vehicles in both directions can be observed.
Radar Speed Meter

Speed Studies
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PHOTOGRAPHIC METHOD
 Time-lapse camera photography can be used.
 Photographs are taken at fixed intervals of time(say one
second per frame) on a special camera.
 By projecting the film on a screen, the passage of any
vehicle can be traced with reference to time.
 Images by video cameras can be also used.

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Traffic Studies
Origin & Destination
Surveys/ Studies

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Traffic Studies
In a transportation study, it is often necessary to know the
exact origin and destination of the trips. The information
yielded by O-D survey includes;
 land-use of the zones of origin and destination
 household characteristics of the trip making family
 time of the day when journeys are made
 trip purpose and mode of travel.
Origin & Destination Surveys/ Studies

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Traffic Studies
Origin is defined as the place where the trip begins and
destination is defined as the place where the trip ends.
• A single movement for a particular purpose from origin to destination is
called a trip.
• People travel to reach their activities at different locations.

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Traffic Studies
Origin-Destination (OD) studies are an important tool for transportation
Professionals. OD studies are conducted to understand the pattern of the
movement of Persons and goods in a particular area of interest during a
particular period of time (Wang, 1997)
 The origin and destination study is carried out
mainly to know the origin and destination of various
vehicles .
 In this study the data collected are, number of
vehicles, their origin and destination, number of
passengers in each vehicle and route etc.

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Traffic Studies
Purpose of OD Surveys
To establish preferential routes for
various categories of vehicles
 To locate place for proposed roads
 To locate new parking palaces & deciding capacity
 To locate expressway route
 To regulate movement of heavy vehicles
 To locate new bridge as per traffic demands

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Traffic Studies
Methods of OD Surveys
 road side interview surveys
 home-interview surveys
 telephone surveys
 taxi surveys
 post card questionnaire surveys
 registration number survey
 tag survey
 public transport survey
 commercial vehicle survey

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Traffic Studies
Information Collected

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Parking Studies
One of the problems created by road traffic is
parking. Not only do vehicles require street space
to move about, but also do they require space to
park where the occupants can be loaded and
unloaded.
The period over which a car is parked is very great
compared with the time it is in motion. Every car
owner would wish to park the car as closely as
possible to his destination so as to minimize his
walking.

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Parking Studies
Traveling vehicles at one time or another will
need to park for short or long times.
 Need for parking spaces is great in areas
where land uses include (business, residential,
or commercial).
 In high density areas spaces are very
expensive, thus the space provided for
automobiles usually has to be divided between
their movement and parking.

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Parking Studies
Congestion
Accidents
Obstruction to fire fighting operations
Effect on environment
ILL Effect of parking

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1. 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.
Parking Studies
ILL EFFECT OF PARKING
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.

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Parking Studies
ILL EFFECT OF 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.
Obstruction to fire fighting operations: Parked vehicles
may obstruct the movement of firefighting vehicles. Sometimes they block
access to hydrants and access to buildings.

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Parking Studies
General Terms of Parking Facilities
 Parking Accumulation :-The total number of vehicles parked in an area at a
specified moment.
 Parking volume:-The number of vehicles parked in a particular area over a given
period of time. It is usually measured in vehicles per day. This does not account for
repetition of vehicles. The actual volume of vehicles entered in the area is
recorded.
 Parking load:-Parking load gives the area under the accumulation curve. It can
also be obtained by simply multiplying the number of vehicles occupying the
parking area at each time interval with the time interval. It is expressed as vehicle
hours.
 Parking duration:-The length of time spent in a parking space.
 Parking turn over:-It is the ratio of number of vehicles parked in a duration to
the number of parking bays available. This can be expressed as number of vehicles
per bay per time duration.

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Parking Studies
Parking Systems
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. Dimensions
of a car can be taken as 5× 2.5 meters and that for a truck is 3.75×
7.5 meters.
1. Parallel parking: The vehicles are parked along the length of
the road. Here there is no backward movement involved while
parking or un-parking the vehicle. Hence, it is the most safest
parking from the accident perspective

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Parking Studies
Parking Systems
2. 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. Delay caused to the traffic is also minimum in
this type of parking.
3. 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.

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Parking Studies
Parking Systems
4. 60◦ parking: The vehicles are parked at 60◦ to the
direction of road. More number of vehicles can be
accommodated in this parking type.
5. Right angle parking: In right angle parking or 90◦
parking, the vehicles are parked perpendicular to the
direction of the road. It consumes maximum road width.
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.

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Parking Studies
Parking Systems

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Parking Studies
Parking Systems
60-degree
90-degree

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Parking Studies
Parking Systems
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. For quick survey purposes, a fixed period
sampling can also be done. 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 1-hour, the count is
again taken. Here there are chances of missing the number of vehicles
that were parked for a short duration.

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Parking Studies
Parking Systems
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.

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Accident Studies
Parking Studies Road accidents cannot be totally
prevented, but by suitable traffic engineering
management measures the accident rate can be
decreased considerably. The various objectives of
accident studies may be listed as below;
 To evaluate existing design
 To support proposed design
 To carry out studies before and after
improvement
 To make financial computations and to give
economic justifications for the improvement
suggested by the traffic engineer.

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Accident Studies
Causes of Road Accidents
 Road User
 The Vehicle
 Road and its conditions
 Environmental factors
 Other causes e.g. incorrect signs and signals, badly
located advertised boards

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Accident Studies
1. Road Users - Excessive speed and rash driving, violation of
traffic rules, failure to perceive traffic situation or sign or signal
in adequate time, carelessness, fatigue, alcohol, sleep etc.
2. Vehicle - Defects such as failure of brakes, steering system,
tire burst, lighting system .
3. Road Condition - Skidding road surface, pot holes, ruts.
4. Road design - Defective geometric design like inadequate
sight distance, inadequate width of shoulders, improper curve
design, improper traffic control devices and improper lighting.
5. Environmental factors -unfavorable weather conditions like
mist, snow, smoke and heavy rainfall which restrict normal
visibility and makes driving unsafe.
6. Other causes -improper location of advertisement boards,
gate of level crossing not closed when required etc..

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Accident Studies
Collision Diagrams
Collision diagrams are used to display and identify similar
accident patterns. They provide information on the type and
number of accidents; including conditions such as time of day,
day of week, climatic conditions, pavement conditions, and
other information critical to determining the causes of safety
problems. Accident reports should be organized by year of
occurrence and accident type for the analysis period.
Accidents that occurred after significant changes in highway
or local land use should not be included.

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Accident Studies
A. Construction of Collision Diagram
Sketch of the collision diagram for either an intersection or a
roadway section using a standard form as shown on the following
page.
1. The sketch need not be to scale.
2. Show the path of each vehicle involved in the accident with
adequate room for information.
3. Place a north arrow for orientation and any other descriptive
information:
a) Location identification
b) Period of analysis
c) Label the roads

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Accident Studies
4. Sketch the path of each vehicle to show vehicle maneuver,
type of collision and accident severity, and;
a) Time of day
b) Day of week
c) Date
d) Lighting condition
e) Pavement condition
f) Other important information, e.g., alcohol
involvement
B. Symbols
Symbols representing the nature of operation, vehicle or object
involved and severity of the accident are adopted. These are
shown in the example collision diagram below. Symbols to
represent types of collisions diagrams are also standardized.

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Accident Studies
Condition Diagrams: The purpose of the Condition Diagram is to
show the intersection and the conditions within the surrounding area
as it exists. The diagram should include the intersection alignment,
items such as;
• Buildings
• Sidewalks
• Trees
• lighting poles
• water hydrants
• stop signs
• number of lanes, and lane use if required, associated with the
streets forming the intersection.
When applicable, the Condition Diagram shall show the length of
all exclusive lanes. The Condition Diagram provides the engineer
with details of field conditions and helps investigate the need for
changes to existing traffic control devices. The diagram should also
be part of an intersection crash analysis.

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Accident Studies
Preparing the Condition Diagram
A. General Details
1. The engineer should enter the Location I.D. so that the
intersection
is thoroughly identified.
2. The name of the highway, highway number, and direction
for both
streets should be included.
3. County, City, Date, and Person(s) preparing the diagram.
4. Orient the intersection by indicating north on the north
arrow.
All items associated with the streets should be drawn using the
symbols as outlined on the bottom of the form.

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Accident Studies
B. Highway and intersection design features, including:
a) Pavement edges, curbs, and shoulders (unpaved or paved)
b) Widths of approaches
c) Approach grades
d) Channelization
e) Parking conditions and restrictions
f) Bus stops
g) Safety lighting or continuous lighting
h) Any other roadway features which may affect traffic operations

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Accident Studies
C. Roadside development, including:
a) Sight distance restrictions (trees, bushes, advertising and other
signs, poles, fences, bridge, and guard rails)
b) Off street parking
c) Driveway locations
d) Utility and other poles
e) Adjacent land use
f) Any other pertinent features
D. Traffic control devices, such as:
a) Signs
b) Traffic signals (type, face locations, etc.)
c) Distance to adjacent traffic signals within 1.61 km (one mile)
(indicate if none)
d) Pavement markings

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Accident Studies
PREVENTION OF ROAD ACCIDENT
Strict punishment should be enforced by govt. if a person
drives in over speed
Tamper proof speed controllers should be installed in all
vehicles.
Two wheelers should not exceeded 50-70km/h.
All the rules should be followed properly by the people.

Traffic studies (transportation engineering)

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Traffic studies (transportation engineering)