Traffic engineering deals with applying scientific principles and techniques to facilitate the safe, efficient movement of people and goods. It aims to achieve free flow of traffic with minimal accidents. Key aspects studied include traffic characteristics, volumes, speeds, origins/destinations, flow, capacity, parking, and accidents. Data is collected through surveys and analysis informs planning, design, operation, and management of road infrastructure.

1. TRAFFIC ENGINEERING

2. WHAT IS TRAFFIC ENGINEERING?
 Traffic Engineering is that branch of civil
engineering which deals with the application of
scientific principles, tools, techniques and
findings for safe rapid convenient economic
movement of people and goods.
 The basic object of traffic engineering is to
achieve efficient, free and rapid flow of traffic
with least no of accidents.

3. STUDY OF TRAFFIC ENGINEERING
 Factual Studies of traffic operations will provide the foundation for
developing methods and for solving specific problems. The study of
traffic engineering may be divided into following sections-
 Traffic Characteristics
 Traffic Studies and Analysis
 Traffic operation-control and regulation
 Planning and analysis
 Geometric Design
 Administration and Management

4. 1. TRAFFIC CHARACTERISTICS
 Road user characteristics- Broadly Classified under
four heads
 Physical Characteristics-Vision, hearing, strength and reaction to traffic
situation
 Mental Characteristics-Knowledge, skill, intelligence, experience, literacy
 Psychological Characteristics-Emotional factors such as fear, anger, anxiety
 Environmental Factors-traffic stream conditions, atmospheric conditions,
facilities to the traffic locality etc.
 Vehicular Characteristics-
 Static Characteristics
 Dynamic Characteristics
 Breaking Characteristics

5. VEHICULAR CHARACTERISTICS
 It is quite important to study the important vehicular characteristics which
affect the design and traffic performance. For economic feasibility the
standards of vehicles should be kept uniform. The vehicular
characteristics are classified as-
 Static Characteristics-It involves dimensions of vehicles( length, width
and height, wheel base, departure and ramp angles, the front, rear and
centre clearances) , weight, maximum turning angle .
 Dynamic Characteristics-Are speed, acceleration, power and breaking
characteristics.

6. 2. TRAFFIC STUDIES
 Also called as Traffic census or surveys.
 It involves analyzing the traffic characteristics for road designs, safe and
efficient movement for traffic and traffic control. These are classified as
following-
I. Traffic volume study
II. Speed studies
III. Origin and destination study
IV. Traffic flow characteristics
V. Traffic capacity study
VI. Parking Study
VII. Accident Studies

7. I. TRAFFIC VOLUME STUDY
 Traffic volume is the number of vehicles crossing a section of road per
unit time at any selected period. The unit for traffic count is generally
taken as vehicles per day or vehicles per hour.
 Traffic volume study are used for various purposes. They are used for
roads improvement and expansion, traffic operation and control,
structural design of pavements, in geometric design, planning and
designing new facilities etc.
 Counting of traffic volume can be done in two ways-
i. Mechanical Counters
ii. Manual Counts

8. HOW TRAFFIC VOLUME DATA IS PRESENTED?
 Traffic volume data can be presented in any of the forms-
a) Annual average daily traffic ( AADT or ADT)-In order to convert the
different vehicles classes to one class such as passenger cars,
conversion factors are known as passenger cars units(PCU)
b) Trends Charts- Useful for planning future expansion, design and
regulation.
c) Variations Charts-These help in deciding the facilities and regulations
needed during peak traffic regulations.
d) Traffic flow maps-These help to find the traffic volume distribution at a
glance.
e) Volume flow diagram-These data are needed for intersection design.
f) Thirtieth highest hourly volume-It is found from the plot between hourly
volume and the no of hours in an year that the traffic volume is
exeeded.

9. II. SPEED STUDIES
 Speed studies are necessary because the actual speed of vehicles over a
particular may vary depending on various factors such as geometric features,
traffic conditions, time, place, environment and driver. Speed studies un be
studied under following heads-
 Travel time- is the reciprocal of speed and is simple measure of how well road
network is operating.
 Spot Speed- Is the instantaneous speed of a vehicle at a specified section or
location.
 Average speed- is the average of the spot speeds of all the passing vehicles at a
given point on the highway.
 Running speed- is the average speed maintained by a vehicle over a particular
stretch of road, while the vehicle is in first motion.
 Overall speed and travel speed- Is the effective speed with which a vehicle
transverses a particular route between two terminals.
 Speed studies gives the general trend in speeds. There are two types of speed
studies carry out-
Spot speed study
Speed and delay study

10. III. ORIGION AND DESTINATION STUDIES
 The origin and destination(OD) study is carry out mainly to-
• Plan the road network and other facilities for vehicular traffic
• Plan the schedule of different modes of transportation for the trip demands
of commuters.
 OD gives information like the actual direction of travel, selection of routes
and length of the trips. It also provides the basic data for determining the
desired directions of the flow or the desire lines. The various applications of
OD surveys are-
 To judge the adequacy of the existing routes and to use it planning new
network of roads, transportation system and mass transit facilities in cities.
 To locate expressway , terminals , new bypass and bridges as per traffic
demands.
 To establish design standards for the road, bridge and culverts along the
route.

11. METHODS FOR COLLECTING O D DATA
 Road Side Interview Method-The vehicles are stopped at previously decided
location, by a group of persons answer to prescribed questionnaire regarding
origin, destination, purpose etc are collected on spot.
Advantage- Data collected quickly, Disadvantage-Vehicles are stopped
 License Plate Method- In this method license plate no are noted under a given
area in a time. After collecting the field data major computation work and
analysis is done in office, by tracking the vehicle no and its time of entering and
leaving.
 Return Post Card Method-Pre paid business reply cards with return address
are distributed along the route to the owners of vehicles. The questionnaire to be
filled by the road user is printed on the cards. The distributing stations for the
cards may be selected where vehicles have to stop as in case of toll both. This
method is suitable for heavy traffic area.
 Tag on Car Method-In this method a pre coded card is struck on the vehicle as
it enters area under study. When the vehicles leave the study area observations
are recorded on the tag. This method is suitable for heavy traffic area.

12. METHODS FOR COLLECTING O D DATA
 Home Interview Method-A random sample of the population is selected and the
residencies are trained personal who collect the travel data from each member
of the house. The data collected is useful for planning road network and various
vehicular facilities.
 Work Spot interview method- The transportation needs of work trips can be
planned collecting the O and D data work at spots like offices, factories,
educational institutions etc.
 O and D data can be presented in the following forms-
i. Origin and destination tables showing no of trips between different zones.
ii. Desire lines plotted in graphical representation prepared in almost all O & D
survey.
iii. Pie Charts
iv. Contour lines

13. IV. TRAFFIC FLOW CHARACTERISTICS
 Traffic stream generally has flow and counter flow along a common
route, unless the stream is separated by one wav flow by proper design
and regulation.
 The basic traffic maneuvers are diverging, merging and crossing.
 Study of traffic flow characteristics includes both transverse and
longitudinal distribution of vehicles in the traffic stream and is useful in
geometric design features such as traffic capacity, volume, number of
lanes and width of carriageways.
 The study is also very much needed to decide traffic regulatory measure
for the design of traffic control methods.

14. V. TRAFFIC CAPACITY STUDIES
 Traffic capacity is the ability of a roadway to accommodate traffic volume.
It is expressed as the maximum no of vehicles in a lane or a road that can
pass at a unit time. Capacity and volume are measures of traffic flow and
have same units.
 Traffic volume is the no of vehicles moving in a specified direction on a
given lane and roadway that pass a given point or cross section during a
specified unit of time.
 Basic Capacity-Is the maximum numbers of passenger cars that can pass
a given point on a lane or roadway during one hour under the most nearly
ideal roadway and traffic conditions which can possibly be attained. Basic
capacity is the theoretical capacity.

15. V. TRAFFIC CAPACITY STUDIES
 Possible Capacity-Is the maximum capacity that can pass a given point
on a lane or roadway during one hour under prevailing roadway or traffic
conditions. The possible capacity is much lower than the basic capacity.
But when the prevailing conditions approach the ideal conditions, the
possible capacity approach the basic capacity. Thus the value of
capacity varies from zero to basic capacity.
 Practical Capacity-Is the maximum number of vehicles that can pass a
given point or roadway during one hour, without density being so great
as to cause unreasonable delay, hazard or restriction to the drivers
freedom to man oeuvre under prevailing roadway and traffic conditions

16. VI. PARKING STUDIES
 Parking studies are useful to evaluate the facilities available. Various
aspects to be investigated during parking studies are-
 Parking Demand- This can be evaluated by different methods.
1. One of the methods is by making cordon counts of the selected area
and recording accumulation of vehicles during the peak hours by
subtracting the outgoing traffic from the traffic volume entering the
cordoned area.
2. Other method is by counting the number of vehicles in the parked area
under study during different periods of the day.
 Parking Characteristics-The study is directed to note the present
parking practices prevalent in the area under consideration and general
problems in parking.
 Parking Space Inventory-The area under study is fully surveyed and a
map is prepared showing all places where kerb parking and offset
parking can be provided to meet the general problems in parking.

17. VII. ACCIDENT STUDIES
 Road accident cannot be totally prevented, but by suitable traffic engineering and
management measures, the accident rate can be decreased considerably. The
various objectives of the accident studies may be listed as-
 To study the causes of accident and to suggest corrective treatment at potential
location
 To evaluate the existing
 To support proposed design
 To carry out studies before and after for improvement
 To make financial computations and to give economic justifications for the
improvements suggested by the traffic engineer
CAUSES OF ACCIDENTS-
 The road users
 The vehicles
 The road and its conditions
 Environmental Factors
 Other causes-Incorrect signs and signals, gate of level crossing, badly located
advertized boards etc.

18. TRAFFIC PLANNING AND ANALYSIS
 Traffic planning plays very important role in traffic engineering. The
improper planning of roadways network and facilities is yet another
reason for accidents and congestions. Hence proper transportation
planning is necessary. The transportation planning process is developed
in a series of stages-
1. Inventories-Information related to land use, economic activity,
population, travel characteristics collected through a series of surveys.
2. Trip Generation-Trip generation concerns with the estimation of number
of trips produce in a given zone. (Trip is defined as the one-way
movement having single purpose and mode of travel between a point of
origin and destination.)
Methods of trip generation- Multiple Regression Analysis
Category Analysis

19. TRAFFIC PLANNING AND ANALYSIS
3. Trip Distribution- In this stage trips generated and attracted from each
are distributed to any other zone. The most important method used for
this procedure is Gravity Model.
4. Model Split-The proportion of total trips between any two zones that
can be shared between the public and private transportation system is
determined in this stage.
5. Traffic Assignment-It is done by a method known as ‘ALL OR
NOTHING’.
6. Plan Preparation and Evaluation-The steps taken above will enable the
various land use strategies and travel demand to be explore.