Chapter 3&4

PREPARED BY
SHIVKUMAR M H [SONOFGOD]
M.E(UVCE),AMIE
ASSISTANT PROFESSOR AND HIGHWAY ENGINEER
EWIT,BANGALORE

UNIT – 3 & UNIT - 4
TRAFFIC STUDIES: Various types of traffic engineering studies, data collection,
analysis objectives and method of study – Definition of study area – Sample size and
analysis.
INTERPRETATION OF TRAFFIC STUDIES: Classified traffic Volume at mid block
and intersections, PCU, origin and destination, spot speed, speed and delay, parking – on
street parking, off street parking, Accident – causes, analysis measures to reduce accident
– problems on above. 6 + 6 = 12 hours
EXAM QUESTIONS
1. Define the term “spot speed study". Explain the presentation of spot speed data.
2. Following data refers to spot speed observations on an road. Analysis and plot the data
to determine: i) Modal speed ii) Median speed iii) Speed for traffic regulation iv)
Speed for geometric design v) Standard deviation of speed value. Top row – speed
kmph, bottom row – number of vehicles observed
3. Explain the uses of i) spot speed studies'.
4. Explain the procedure to find out spot speed using enoscope. How the data is represented
5. Enumerate the different methods of traffic volume studies. Discuss objects and uses of
traffic volume studies.
6. Write a short note on moving car observer method with its advantages.
13 18 23 29 32 38 43 48 53 58
4 11 20 30 55 45 22 11 6 2

7. Mention the various methods of carrying out speed and delay study. Explain any two of
them.
8. Explain briefly speed and delay study by moving car method.
9. Explain the uses of i) journey speed and delay studies.
10. Explain the objectives of 0 and D studies
11. Explain the objectives of travel time and delay studies and 0 & D studies. Describe how
travel time is and delay data are presented.
12. List the applications 0 and D studies.
13. Explain various forms of presenting 0 and D data.
14.Explain the objective of origin and destination studies. With the help of a neat sketch,
demarcate the study zone.
15.Explain the meaning of following terms, with examples i) Parking accumulation ii)
Parking index iii) Parking turn over.
16.Explain the on street parking and off street parking
17.Discuss the purpose of parking study. Explain the steps involved in forecasting parking
demands.
18. Discuss the various types of parking, their advantages and disadvantages.
19.Mention the objectives of accident studies also mention the various causes of accidents.
20.With a neat sketch. Explain collision and condition diagram related to accident studies
21.Explain the following Terms in accidents: measures to reduce accidents condition
diagram and collision diagram.
22. Explain the various preventive measures to reduce accidents.
23.Describe the' characteristics of accidents.
24.Explain what is 30th highest hourly volume and its importance.

25.What is PCU? List the factors which affect the PCU values of different vehicle classes
26.Explain the terms: i) Design hourly volume ii) Design vehicle iii) Spot-speeds.
27.Mention the various factors that affect the road user characteristics explain briefly any two
of them
28.Explain with neat sketch, PIEV theory in analyzing driver reaction time and its
significance. Indicate how it is different from SSD and OSD calculations. Discus factors
influencing perception reaction time.
29.List and explain the various static and dynamic characteristic of vehicles in designing
traffic facilities. Indicate the data needing for multilevel parking system for cars and two
wheelers
30.List and explain with equations the various resistances considered for power calculation of
vehicles. Give the values of various constants used in equations.
31. Explain the various forces that offer resistance to motion of a vehicle.
32.Which are the design elements affected by length, speed, power and braking
characteristics of vehicles.
33.Explain physiological factors affecting driver performance.
34.Describe visual aspects of road users affecting highway design.
35.Discuss classified traffic volume at mid-block and intersections
36.Define the study area and explain sample size and analysis.

Different traffic engineering studies generally carried out are:
(1) Traffic volume studies
(2) Spot speed studies
(3) Speed and delay studies
(4) Origin and destination studies
(5) Parking studies
(6) Accident studies
SPOT SPEED STUDIES
• Spot speed is referred to as the instantaneous speed of a vehicle at a point or cross
section;
• There are two distinctly different methods of determination of spot speeds.
• In the first method, the time, t (sec) taken by the vehicle to travel a short distance, d (m)
is determined.
• Therefore the speed, v = (d/t) m/sec.
• In the second method, the instantaneous speed is measured by a pre-calibrated 'radar'
equipment which displays or records the speed in desired units, such as kmph.
• There are two definitions, for the average of a series of spot speed measurements viz.:,-
'space-mean speed' and 'time-mean speed'.

SPACE-MEAN SPEED
• Space-mean speed represents the average speed of vehicles in a certain road length at any
time.;
• Space-mean speed is calculated from the relation.
Vs = 3.6*d*n/∑n
i= 1 * ti
where Vs = space-mean speed, kmph
d= length of road or the distance considered, meter ,
n = number of individual vehicle observations
t(i) = observed travel time, (sec) for each vehicle to travel the distance, d in meter
• The average travel time of all the vehicles is obtained from the reciprocal of space-mean
speed.
TIME-MEAN SPEED
• Time-mean speed represents the speed distribution of vehicles at a point on the roadway
• It is the average of instantaneous speeds of observed vehicles at the-spot.
• Time-mean speed is calculated from the relation:
Vt = ∑n
i= 1 V(i)/ n
where V(t) = time-mean speed, kmph
V(i) = observed instantaneous speed of vehicle, kmph,
n = number of vehicles observed
• The space-mean speed is slightly lower than time-mean speed under typical speed
conditions on rural highways.

Example - Speed observations from a radar speed meter have been taken, giving the
speeds of the subsidiary streams composing the flow along with the volume of traffic of
each subsidiary stream. The readings are as under : Calculate: (i) Time-mean speed
(ii) Space-mean speed (iii) Variance about space mean speed.
Speed
(km/hr)
Volume of subsidiary
stream
(Vehicle hour)
2-5 1
6-9 4
10-13 0
14-17 7
18-21 20
22-25 44
26-29 80
30-33 82
34-37 79
38-41 49
42-45 36
46-49 26
50-53 9
54-57 10
58-61 3

Solution: The mid-point of speed class v(i) and q (i)are tabulated below, along with and
v(i)*q(i) and k(i) = q(i)/v(i)
450 veh/hr
km/hr
km/hr
Speed
Range
Volume
q(i)
Speed mid-
point v(i)
q(i)*v(i) k(i) =
q(i)/v(i)
2-5 1 3.5 3.5 0.29
6-9 4 7.5 30.0 0.54
10-13 0 11.5 0 0
14-17 7 15.5 108.5 0.45
18-21 20 19.5 390.0 1.02
22-25 44 23.5 1034.0 1.87
26-29 80 27.5 2200.0 2.91
30-33 82 31.5 2583.5 2.60
34-37 79 35.5 2804.5 2.23
38-41 49 39.5 1935.5 1.24
42-45 36 43.5 1566.0 0.83
46-49 26 47.5 1235.0 0.55
50-53 9 51.5 493.5 0.17
54-57 10 55.5 555.0 0.18
58-61 3 58.5 178.5 0.05
∑450 ∑15087.0 ∑14.93

Problem - Twenty five spot speed observation were taken and were as under:
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. Calculate : (i) Time – mean speed (ii) space-mean speed and verify the relation
between the two.
The relationship between and is :
This may be compared with the value of 49.56 obtained earlier.

SPOT SPEED STUDIES ARE USEFUL IN THE FOLLOWING ASPECTS OF
TRAFFIC ENGINEERING
(a) Planning traffic regulation and control measures such as speed limit. etc.
(b) Design or redesign of various geometric elements of the road
(c) To decide the design speed of existing or new facilities
(d) In accident studies and preventive measures
(e) Study of traffic capacity
(f) To find the speed trends with respect to last several years
(g) To compare the behaviour of diverse types of drivers and vehicles under specified
set of conditions.
MEASUREMENT OF SPOT SPEEDS
 One of the earliest methods of determining spot speed of a vehicle is by finding the
time taken to cover a short distance.
Procedure
 The selected distance (d, m) may be marked on the pavement surface and the time
taken (t sec) for a vehicle to traverse this distance may be measured either manually
using a timer from an elevated location or recorded automatically using set of
appropriate sensors.
 The speed, v is given by: v = (d / t) m/sec.
 Other equipment used for spot speed measurements are graphic recorder, electronic
meter, photo electric meter, photographic methods and using radar speed meter.
 Of all these methods, the radar speed meter method seems to be the most efficient
one as it is capable of measuring the spot speeds instantaneously and also recording
them automatically; the accuracy of measurement is also reasonably good.

Procedure
 The radar speed meter-directs a radar" or audio beam of a certain frequency at the
moving vehicles.
 The reflected signal is shifted in frequency and the difference in frequency is
proportional to the speed of the vehicle;
 The spot speeds of desired number of vehicles of each class (so as to obtain the desired
sample size) are determined during the sampling periods of the day, days of the week
and months of year
Location of setup
 The radar speed meter should be located as close as possible to the line of vehicle travel.
 The equipment may be' set up at an angle between the direction of travel of the vehicle
and a straight line from the transmitter receiver.
 In order to minimize the possible errors, it is desirable that the vertical and horizontal
angles to the vehicle is its less as possible, preferably less than 20°.
Advantages
 The radar speed meter is pre-calibrated to display/record the vehicle speed in kmph.
 The radar speed meters are capable of measuring speeds of vehicles from about 5 kmph
to over 300 kmph, as may be required for measurement of speeds of cars during the car-
race.
 The present day radar speed meters have provision for taking photographs of the
vehicles along with the display of the speed of the vehicles at that instant.
 Simple hand held radars of small size are also available.
Disadvantage
 One of the disadvantages of this type of equipment is that when more than one vehicle is
trapped, the speed of the closest vehicle only will be recorded.

PRESENTATION OF SPOT SPEED DATA SPEED DISTRIBUTION TABLE
• From the spot speed data of the selected samples, frequency distribution table of spot
speed data is prepared by arranging the speed groups covering desired speed ranges (such
as 10 - 20 kmph , 20-30 kmph , 30 - 40 kmph, etc. ) and the number of vehicles in each
speed range.
• The arithmetic mean of the measured speeds is taken as the average spot speed of all the
vehicles in the stream.
• It is possible to determine either the average spot speed of any desired vehicle class (such as
car, HCV, etc.) or the combined weighted average speed of all the vehicles in the traffic
stream.
• The table gives the general information of the speeds maintained on the section and also
regarding the speed distribution pattern.
• This is illustrated later in the Example 5.6.
FREQUENCY DISTRIBUTION DIAGRAM OF SPOT SPEEDS
• The average values of each speed group of vehicles on the X-axis
• The percentage of vehicles in that group on the Y-axis
• A graph is plotted as shown in Fig. 5.4.
• This graph is called the frequency distribution diagram of spot speeds.
• This diagram will have a definite peak value of travel speed across the section and this
speed is denoted as 'modal speed'.
• It may be inferred that maximum proportion of vehicles in stream prefers to travel at
about this modal speed on this particular location of the road

'CUMULATIVE SPEED DISTRIBUTION DIAGRAM'
• A graph is plotted with the average values of each speed group on the X-axis and the
cumulative percent of vehicles at or below the different speeds on the Y-axis, as
shown in figure.
• This graph is called 'cumulative speed distribution diagram'
 From this diagram, the '85th percentile speed' is determined i.e., the speed at or
below which 85 percent of the vehicles are passing the point on the highway can be
assessed;
 In other words, only 15 per cent of the vehicles exceed this speed at that spot.
 The drivers exceeding 85th percentile speed are usually considered to drive faster
than the safe speed under existing conditions
 Hence this speed is adopted for the 'safe speed limit' at this zone.
 Therefore if a 'speed limit' regulation sign is to be installed at an accident prone
location, spot speed studies are carried out during different periods of the day,
cumulative speed distribution diagram is plotted and 85" percentile speed is adopted
as the upper speed limit.
• On some arterial roads where slow moving vehicles are to be prohibited,15th
percentile speed may be determined from the cumulative speed distribution
diagram.
• The 15th percentile speed is considered to represent the lower speed limit, to
prohibit slow moving' vehicles to decrease delay and congestion.
• For the purpose of checking the requirements of highway geometric design elements,
the 98th percentile speed is generally taken as the 'design speed' of the existing
'roadway facility.

SPEED DISPERSION
• All vehicles do not travel at the same speed at a location of 'a road.
• If there is 'free flow' of vehicles, the speed distribution generally follows a normal distribution
curve.
• The amount of spread of speeds from the average speed affects both capacity and safety.
• This spread in speeds is represented by 'speed dispersion'.
• The quality of flow of vehicles in a traffic stream may be represented in terms, of the speed
dispersion.
• The speed dispersion may be judged by several methods such as,.
(a) 85th minus 15th percentile of spot speeds, (b) standard deviation of spot speeds or (c) the
coefficient of variation of spot speeds.

Example - 1
The table below gives the consolidated data of spot speed studies on a section of a road.
Determine the most preferred speed at which maximum proportion of vehicles
Solution
 Using the data from spot speed studies, frequency distribution table of spot speeds is
prepared for as given in Table 5.3 below
 The frequency distribution curve is plotted as shown in Fig. 5.4, using the mean speed of
column (2) of Table 5.2 on the X – axis and the percent frequency values of column of
vehicles travel is the modal speed corresponding to the peak value of the frequency which
can be obtained from this frequency distribution diagram (see Fig. 5.4)
 The most preferred speed value is the modal speed and diagram plotted as in Fig. 5.4. the
modal speed corresponding to the peak value is found to be 47 kmph.
Speed range,
kmph
No. of speed
observations
Speed range,
kmph
No. of speed
observations
0 – 10 0 50 – 60 216
10 – 20 11 60 – 70 68
20 – 30 30 70 – 80 24
30 – 40 105 80 - 90 0
40 – 50 233

Speed
range,
kmph
Mean speed
observation
s
Frequenc
y
f
Percent
frequenc
y
1 2 3 4
0 – 10 5 0 0.0
10 – 20 15 11 1.6
20 – 30 25 30 4.4
30 – 40 35 105 15.3
40 – 50 45 233 33.9
50 – 60 55 216 31.4
60 – 70 65 68 9.9
70 – 80 75 24 3.5
80 - 90 85 0 0.0
Total: 687 100.0

Example -2
Spot speed studies were carried out at a certain stretch of a highway with mixed traffic
flow and the consolidated data collected are given below.
Determine: (i) the upper and lower values or speed limits for installing speed regulation
signs at this road stretch ,(ii) the design speed for checking the geometric design
elements of the highway and (iii) Speed dispersion
Speed range,
kmph
No. of vehicles
observed
Speed range
kmph
No. of vehicles
observed
0 to 10 12 50 to 60 255
10 to 20 18 60 to 70 119
20 to 30 68 70 to 80 43
30 to 40 89 80 to 90 33
40 to 50 204 90 to 100 9

Solution
This problem may be solved in three stage. First a frequency distribution cable is
prepared using the given spot speed data, next the cumulative frequency distribution
diagram is drawn and finally the appropriate values are obtained from the graph.
(1) Frequency distribution and cumulative frequency values of spot speeds
Frequency distribution table of spot speed data is prepared. See Table 5.4. Column no.,
2 of the Table represents the average values of the different speed ranges. Column no.3
gives the number of vehicles observed in each speed range and is represented as the
frequency, f. The frequency values expressed as a percentage of the total number of
vehicles observed in all the speed ranges is given in column no. 4. The cumulative
percent of vehicles travelled at or below the different speeds are given in column no. 5.
(2) Cumulative spot speed distribution diagrams
The cumulative spot speed distribution diagram is drawn by plotting the mid speed
values of column (2) of Table 5.4 on the X-axis and the % cumulative frequency values
of vehicles travelling at or below the specified speed given column (5) of the Table on
the Y-axis, as shown in Fig. 5.5. From the cumulative speed distribution diagram the
following values are obtained.
(3) Desired speed values
(a) Upper speed limit for regulation = 85th percentile speed = 60 kmph
(b) Lower speed limit for regulation = 15th percentile speed = 30 kmph
(c) Speed to check geometric design elements = 98th percentile speed = 84 kmph
(d) Speed dispersion = 85th percentile speed - 15th percentile speed = 60 kmph - 30 kmph
= 30 kmph

Table 5.4 Frequency distribution and cumulative frequency values of Spot speed
data (Example 5.7)
Speed
range,
kmph
Mid
speed
kmph
Frequency
f
Frequency
%
Cumulative
frequency
(at or below
the speed).
%
(1) (2) (3) (4) (5)
0 – 10 5 12 1.41 1.41
10 – 20 15 18 2.12 3.53
20 – 30 25 68 8.00 11.53
30 – 40 35 89 10.47 22.00
40 – 50 45 204 24.00 46.00
50 – 60 55 255 30.00 76.00
60 – 70 65 119 14.00 90.00
70 – 80 75 43 5.06 95.06
80 - 90 85 33 3.88 98.94
90 - 100 95 9 1.06 100.00
Total: 850 100.0

ENOSCOPE
 A simple device called enoscope eliminates the parallax effect that creeps in when the direct
readings are taken by one observer.
 This device is also known as mirror box is an L shaped box , open at both ends , with mirror set
at 45degree angle to the arms of the instrument, as shown in figure.
 The instrument bends the line of sight of observer so that is perpendicular to the path of vehicle.
 The method can be used with one enoscope or two enoscopes.
 If one enoscope is used the instrument is placed directly opposite the first reference point and
observer stations himself at the other reference point as shown in figure 3.2
 The stop watch is started as soon as the vehicle passes the first reference point and is stopped as
soon as it passes the observer
 If two enoscopes are used , the observer stations himself mid way between the two reference
points and starts the stop watch as soon as the vehicle crosses the first reference point and stops
the stop watch when it crosses the second reference point

SPEED AND DELAY STUDIES
Objects and uses of speed and delay studies
• The speed and delay studies give the particulars of running speeds or the fluctuations
in speeds, the locations and duration of delays or stoppages and 'the overall travel speed
between two desired locations along a road.
• The results of the speed and delay studies are useful in identifying the locations of
congestion, the causes and in arriving at a suitable improvement measures to reduce
the delays or increase the travel speed.
• The studies are also utilized to find the travel time before and after the proposed
improvements and in 'benefit-cost analysis
• In general the efficiency of the roadway and the level of service is judged from the
overall travel speed and the type of delays.
 The delay or the time lost by traffic during the travel period may be either due to
fixed delays or operational delays. Fixed delays occur primarily at intersections due to
traffic signals and at level crossings.
 Operational delays are caused by the interference of traffic movements, such as
turning vehicles, parking and un-parking of vehicles, pedestrians, etc. and by internal
friction in the traffic stream due to high traffic volume, insufficient capacity and by
accidents.
 Therefore the overall travel speed between the origin and destination points of travel
is invariably lower than the desired running speed.

METHODS OF CONDUCTING SPEED AND DELAY STUDIES
There are different methods of carrying out speed and delay studies;
(a) Floating car or riding check method
(b) License plate or vehicle number method
(c) Interview technique
(d) Elevated observations
(e) Photographic technique
FLOATING CAR METHOD OR MOVING OBSERVER METHOD OR CAR
MOVING METHOD FOR RUNNING SPEED AND JOURNEY SPEED
• In the 'floating car method', a test vehicle is driven over a given route of travel at
approximately the average speed of the stream, thus trying to 'float' with the traffic
stream.
• A number of test runs are made by the test vehicle along the study stretch.
• A group of observers are seated in the test vehicle to record various observations
during each run of the test vehicle.
 One observer is seated in the test car with two stop watches or timers;
 One timer is used to record the time of arrival of the-test car at various control
points like intersections, bridges or any other fixed points during each trip
 and the other stop watch is used to find the duration of individual delays.

 The time, location and cause of these delays during each test run are recorded by the
second observer either on suitable tabular forms or by voice recording equipment.
 The number of vehicles overtaking the test vehicle and the number overtaken by the
test vehicles are noted in each test run by a third observer.
 The number of vehicles travelling in the opposite direction in each test run is noted
by a fourth observer.
 In this method all the required details of speed and delay including location, duration
and causes of delay are obtained during each test run.
 The average journey time t , in minutes (min) for all the vehicles in a traffic stream in
the direction of flow, q is given by:
t (bar) = tw - ny/q
q = na + ny /ta +tw.
q = Flow of vehicles (volume per min), in one direction of the 'stream'.
na = Average number of vehicles counted in the direction of the stream q when the
test vehicle travels in the opposite direction or against the stream.
ny = The average number of vehicles overtaking the test vehicle minus the number of
vehicles overtaken when the test is in the direction of the stream, q.
tw = Average journey time, (min) when the test vehicle is travelling with the stream, q.
ta = Average journey time, (min) when test vehicle is running against the stream, q.
 The application of floating car or riding check method is illustrated in the Example 5.8
given below.

ADVANTAGES
1. The method gives an unbiased estimate of flow.
2. It is economical in man power as compared to the stationery observer method.
3. It enables the data on speed and flow to be collected at the same time.
4. It gives mean values of flow and speed over a section ,rather than at a point .
- Thus it gives directly the space mean speed .
- Where as spot speed studies gives time mean speed
5. It gives additional information on stops at intersections, delays, parked vehicles
USES OF JOURNEY SPEEDS AND DELAYS
1. The cost of the journey depends upon the speed at which it is made.
2. Journey time studies on a road net work in a town are useful to evaluate congestion,
capacity, level of service and need for improvements
3. In transportation planning studies, the determination of travel time is necessary for
carrying out the trip assignment .
4. Before and after studies pertaining to journey time are useful for assessing
effectiveness of improvement measures
5. Delay studies at intersections provide the data for the design and installation of the
appropriate traffic control device

LICENSE PLATE OR VEHICLE NUMBER METHOD
• In this method, stop watches/timers or voice recording equipment are used.
• Observers are stationed at the entrance and exit of the test stretch where information of travel
time is required.
• The timings and the vehicle numbers are noted by the observers of the selected sample of
vehicles in the stream.
• From the office computations, travel time of each vehicle could be found.
• But the method does not give important details such as causes of delays and the duration and
number of delays within the test 'stretch.
• Also the office computations are cumbersome and time consuming.
INTERVIEW TECHNIQUE
• In the interview technique, the work can be completed in a short time 'by interviewing and
collecting the required details from the road users on the spot.
• However the data on delays collected depend on the assessment of each individual driver and
are likely to be subjective.
• Also this method and may not provide with-all the required details correctly.
ELEVATED OBSERVATION AND PHOTOGRAPHIC TECHNIQUE
• Observers with timers are located at an elevated observation point from where the movement of
most of the vehicles within the desired stretch or intersection area could be observed.
• Alternatively cameras or video equipment are located and the desired observations recorded.
• Elevated observation and photographic techniques are thus useful for studying the speed and
delay characteristics on short test stretches or at intersection areas
• Intersection delays studies need special attention as this poses a major problem to the traffic
engineer.
• Such studies at each intersection will help in evaluating the efficiency and effectiveness of the
control device like signal system, the remedial measures for accidents etc.

Example – 3
The consolidated data collected from speed and delay studies by floating car method on a
stretch of urban road of length 3.5 km , running North – South are given below .
Determine the average values of (i) Volume (ii) journey speed and (iii) running speed of
traffic stream along each direction
Trip
No.
Direction
of trip
Journey
time
min –
sec
Total
stopped
delay.
Min – sec
No. of
Vehicles
Overtaking
No. of
Vehicles
Overtaking
vehicles
from
opposite
direction
1 N - S 6 – 32 1 – 40 4 7 268
2 S - N 7 – 14 1 – 50 5 3 186
3 N - S 6 – 50 1 – 30 5 3 280
4 S – N 7 – 40 2 – 00 2 1 200
5 N - S 6 - 10 1 – 10 3 5 250
6 S - N 8 - 00 2 – 22 2 2 170
7 N - S 6 – 28 1 – 40 2 5 290
8 S - N 7 - 30 1 - 40 3 2 160

Solution
The mean values of journey time, stopped delay, number of vehicles overtaking
overtaken and in opposite direction for North-South-and South-North directions are
obtained from Table 5.5 given below.
Table 5.5 Mean values of speed and delay data (Example 5.8)
Direction
Journey
time
min – sec
stopped delay.
Min – sec
Overtaking Overtaken
In
opposite
direction
N - S 6 - 32 1 - 40 4 7 268
6 - 50 1 – 30 5 3 280
6 - 10 1 - 10 3 5 250
6 - 28 1 – 40 2 5 290
Total: 26 - 00 6 – 00 14 20 1088
Mean: 6 - 30 1 – 30 3.5 5.0 272
S – N 7 - 14 1 – 50 5 3 186
7 - 40 2 – 00 2 1 200
8 - 00 2 - 22 2 2 170
7 – 30 1 – 40 3 2 160
Total : 30 – 24 7 - 52 12 8 716

(a) North – South direction
= average no. of vehicles overtaking minus overtaken
average no. of vehicles during trips in opposite direction (for S – N trip = 179)
average journey time with the stream, q = 6 min 30 sec = 6.5 min
= average journey time during trips against the stream= 7 min 36 sec = 7.6 min
Average volume, q = veh/min
Average Journey time min
Average journey speed km/min kmph
Average stopped delay = 1.5 min
Average running time = Average journey time – average stopped delay = 6.62 - 1.5= 5.12min
Average running speed kmph
(b) South – north direction
min min
veh/min min
Journey speed kmph
Average stopped delay = 1.66 min
Average running time = 7.55- 1.66 = 5.89 min
Average running speed = (3.5 * 60)/5.89 = 35.65 kmph

ORIGIN AND DESTINATION STUDIES
Objects
 Origin and destination studies (0 & D studies) give information on the actual location
or zone of origin of travel of vehicles or individual passenger trips and their
destination; these studies provide details such as direction of travel, selection of routes,
trip length and the frequency and number of such trips.
 The study area may cover the entire country or a selected region within the country
or state or within a 'city or any identified area.
 The 0 & D studies provide the basic data for determining the desired directions of
vehicular flow or passenger trips in terms of the 'desire lines'.
 Desire lines are straight lines joining the points of origin and destination of each trip.
• O & D studies on vehicular traffic are essential for either comprehensive planning of
new road network or for improvements in the existing road network.
• The 0-D data on vehicular traffic are also useful for planning and design of
expressways, bypasses around congested towns and cities, location for truck
terminals, truck lay-byes/rest areas. etc.
• The routes and their schedules could also be scientifically planned using the data of
the study.
• The future traffic needs may be also be estimated by extrapolating the data from 0 &
D studies and the socio-economic studies.

APPLICATIONS
(a) To judge the adequacy of existing routes and to plan new network of roads.
(b) To establish design standards for the road, bridges and culverts along the route.
(c) To locate expressways or major routes along the desire lines.
(d) To establish preferential routes for various categories of vehicle including bye pass.
(f) To plan transportation system and mass transit facilities in cities including routes
and schedules of operation.
(g) To locate terminals and to plan terminal facilities
(h) To locate intermediate stops of public transport.
METHODS OF CONDUCTING 0 & D STUDIES
 There are a number of methods for collecting the 0 & D data.
 Some of the methods commonly adopted are:
(a) Road-side interview method
(b) License plate method
(c) Return post card method
(d) Tag-on-car method; and
(e) Home interview method
 Each method has its own advantages and limitations.
 The choice of the method is made judiciously depending on the objective and location

RETURN POST CARD METHOD
• Pre-paid business reply post cards with return address are distributed to the road
users at some selected points along the route or the cards are mailed to the-owners of
vehicles.
• The questionnaire to be filled in by the road user is printed on the card, along -with
a request for co-operation and purpose of the study.
• The distributing stations for the cards may be selected where vehicles-have to stop as
in case of a tollbooth or signals.
• The method is suitable where the traffic is very heavy.
• The person need not be skilled or trained just for distributing the cards, Only a part
of the road users may return the cards promptly after filling in the desired details
properly and correctly.
• The conclusions drawn may not represent the entire population.
TAG ON - CAR METHOD
• In this method a pre-coded card is stuck on the vehicle as it enters the area under
study.
• When the car leaves the cordon area the other observations are recorded on the tag.
• This method is useful where the traffic is heavy and moves continuously.
• But the method gives only information regarding the points of entry and exit and the
time taken to traverse the area.

ROAD SIDE INTERVIEW METHOD
 The vehicles are stopped at selected interview stations by a group of persons and the
answers to prescribed questionnaire are collected on the spot and entered in the
prescribed forms.
 The information collected include the place and time of origin, and, destination,
route, locations of intermediate stoppages if any, purpose of the tripe type of vehicle,
number of passengers in each vehicle, etc.
 Both the road side interview study on selected sample of each vehicle class and
classified traffic volume study of the total traffic flow are to be conducted
simultaneously during the same time periods;
 Part of the traffic may be filtered and diverted through a prescribed lane with the
help of the police and warning signs so that the drivers of the selected sample of vehicles
are interviewed.
 The answers, to the set of questionnaire are noted by the observers
 The vehicles are allowed to proceed with minimum possible delay.
• In this method the data can be collected in short duration and the field organization
is simple and the team can be trained quickly.
• The main drawback of the method is that when some of the vehicles are stopped for
interview, road users as there is some delay during the data collection;
• Also to prevent undue congestion due to the stopped vehicles, there should be
sufficient space across the roadway at the location for the survey.

LICENSE PLATE METHOD
 The entire area under study is cordoned out and the enumerators are simultaneously
stationed at all observation stations at the locations of entry and exit on all the roads
leading in and out of the area.
 Each group of enumerators at the observation station is given timers and they note
the license plate numbers (registration numbers) of the vehicles entering and leaving
the cordoned area and the time.
 Separate recording sheets are maintained for each direction of movement for a
specified time interval.
 After the collection of the field data, the major work will be office computations and
analysis, by tracking each vehicle number and its time of entering and leaving the
cordoned area and also those passing through some of the intermediate stations.
• This method is quite easy and quick as far as the field work is concerned; the field
organization can also be trained quickly; the method is suitable for a small study
area.
• The method however involves lot of office computations in tracing the trips through
a network of stations within the cordoned area in addition to the entry and exit
points;
• A sizable number of teams are required to take simultaneous observations;
• It is not possible to collect several details such as frequency of trips, purpose, etc

HOME INTERVIEW METHOD
 The home interview method of O-D studies is preferred when comprehensive traffic
and transportation requirements are to be planned for a city.
• A random sample of 0.5 to 10 percent of the population it selected depending on the
total number of residences.
• It is desirable to classify the types of the households in the entire study area and then
randomly select the samples from each class.
• The residences are visited by the trained persons and they collect the travel data
from each member of the house hold.
• Detailed information regarding the trips made by the members are obtained on the
spot.
• The data collected will be useful either for planning the road net work and other
roadway facilities for the vehicular traffic or for planning the mass transportation
requirements of the passenger trips or for both the requirements.
 The problem of stopping vehicles and consequent difficulties are avoided altogether.
 The present travel needs are clearly known and the analysis is also simple.
 Additional data useful for forecasting traffic and transportation growth.
 But to have complete coverage of the entire cross section of the population is very
expensive and tedious.

WORK SPOT INTERVIEW METHOD
• The transportation needs of work trips can be planned by collecting the 0 & D data at work
spots like the offices, factories, educational institutions, etc. by personal interviews.
CHOICE OF METHOD OF STUDY
• While planning for 0 and D studies at a place, it is necessary to decide most appropriate
the method of study.
• The selection of the method is dependent on the objective, the study area, funds and time
available.
• The influence of year and period of traffic/availability of persons of the house hold who
could respond properly to the questionnaire should be known.
• Care is needed in selecting the method of data collection and sampling method and size.
SAMPLING IN O-D STUDIES
• It is desirable that O-D survey should cover as high percentage of traffic or the
population.
• However in larger cities or when the study area or the population is huge, the total number
of house hold units to be covered in the case of 'home interview method' becomes too
large;
• similarly when the traffic flow on the roads is high, the number of vehicle drivers to be
covered in the-case of road side interview method also will be quite high.
• In such cases it becomes necessary to resort to appropriate sampling technique and to
arrive at the appropriate sample size.
• The sample size should be decided keeping in view the desired accuracy and cost of data
collection and analysis.

PRESENTATION OF 0-D DATA
 Origin and destination tables are prepared showing number of trips between
different zones.
 'Desire lines' are plotted which is a graphical representation prepared in almost all 0
and D surveys.
 Desire lines are straight lines connecting the origin points with-destinations,
summarized into different area groups
 The width of such desire lines is drawn proportional to the number of trips in both
directions.
 The desire line density map helps to decide the actual desire of the road users and thus
helps to find the necessity of a new road link, a diversion, a by-pass or a new bridge.
 These desire lines be compared with the existing flow pattern along the existing routes
by superimposing one over the other with the help of tracing sheets.
 Similarly the desire line diagram showing the passenger trips is useful to scientifically
plan the mass transport facilities or the need to provide direct routes between certain
zones
 The relative magnitude of the generated traffic and geometrical relationships of the
zones involved may be represented by 'pie charts', in which circles are drawn; the
diameter being proportional to the number of trips
 Contour lines may be plotted similar to topographic contours.
 The shape of the contours would indicate the general traffic need of the area

PARKING STUDIES
NEED FOR PARKING
• Though the roadway width including the number of lanes are decided based on the
design traffic flow or volume, all the vehicle's do not keep moving during the entire day.
• Some portion of the traffic will need to stop or park at the desired locations for
different durations.
• For example, those who use their vehicles for travel to a market area may need
parking facility for short durations until they complete the purchases; but those who
work in the shopping establishments will need parking facility for long duration.
• The commercial vehicles need space near the destination for loading/unloading
operations.
• The demand by automobile users for parking space is one of the major problems of
highway transportation, especially in metropolitan cities.
• In industrial, commercial and residential places with multi-storied buildings, parking
demand is particularly high.

EFFECT OF PARKING ALONG ROAD SIDE
• Even a few vehicles parked along the road side will reduce the effective width of the
carriageway for the moving traffic and result in substantial reduction in the roadway
capacity.
• Therefore road side parking facility may be made available only on wide stretches of
the road, during the period of the day when the traffic flow is low.
• However road side parking will have to be prohibited on congested roads with heavy
vehicular flow.
INVESTIGATIONS FOR PARKING STUDIES
Different aspects to be covered during parking studies are
(a) Study of existing parking characteristics and the facilities available
(b) Inventory of additional parking space that could be availed
(c) Determination of the actual parking demand during different periods of the day
(d) Planning and design of suitable parking facilities that are suitable to meet the
demand keeping in view the available space for parking facility
PARKING CHARACTERISTICS
• In case of road-side parking or 'kerb parking', it is also necessary study the parking
pattern, interference to smooth flow of traffic caused during parking and un-parking
operations and the accidents involved during parking operations.
• In the case of off-street parking, the minimum, maximum and average values of
walking distance' to reach different destinations after parking the vehicles are to be
worked out.

PARKING SPACE INVENTORY
• The area under study is fully surveyed and a map is prepared showing all places
where kerb parking and off-street parking facilities can be provided to meet the
parking demand.
• While designing appropriate parking facilities, the traffic engineer has to take into
consideration the important factors such as:
(i) Traffic flow along the adjoining roads
(ii) Roadway capacity
(iii) Parking demand and
(iv) Maximum parking space that can be made available for different class of vehicles.
PARKING DEMAND
• The term 'parking accumulation' indicates the total number of vehicles that are,
parked in a given area during a specified time period.
• Depending on the timing of the day and the location, the parking demand increases
from early morning and reaches a peak value during the period of heavy parking demand
and later in the night, it decreases.
• If a curve is plotted with X-axis showing the timing of the day and the Y-axis showing
the parking demand, the area under the parking accumulation curve is an indicator
of the parking demand.
• Parking duration is the length of time a vehicle spends in a parking space.
• Parking occupancy is the number of spaces occupied in a parking lot, expressed as a
percent of total parking spaces available.
• Parking turnover is usually calculated as the number of times a parking space has
been used during the day.

DETERMINATION OF PARKING DEMAND
• This method is useful when the parking demand is less than the space available for
parking.
• One of the methods is by counting the number of vehicles parked in the area under
study during different periods of the day.
• By noting the registration number of each parked vehicle at any desired time interval
(such as 30 minute, one hour, etc.)
• It is possible to estimate the duration of parking of each vehicle at the parking area.
• However if the parking lot gets filled up during the peak demand periods
• It is obvious that actual parking demand is likely to be higher and therefore
• this method fails in the estimation of the actual peak demand.
 Another method is by making cordon counts of a relatively larger area: around the
locality with high parking demand
 The accumulation of vehicles in the selected area is obtained by subtracting the
outgoing traffic from the traffic volume entering the cordoned area during the study
period.
 However by this method it is not possible to obtain the duration and the specific
locations of parking.
 An useful method of field study is by interviewing the drivers of parked vehicles,
shop owners and other vehicle owners in the locality.
 It is possible to obtain details of information such as desired parking period of the
day, preferred locations, frequency, amount of parking fee willing to pay, etc.
 This method is very useful when the parking demand in the study area is higher than
the total parking space available.

On-Street or Kerb parking
Types of kerb parking
 In this type if parking, vehicles are parked
along the kerb which may be designed for
parking,
 Kerb parking is quite convenient for those
who could find a suitable space to park their
vehicles near the place they wish to stop:
 but for others who could not find a parking
space it is a problem and often they
may have to park their vehicle at a far
off place and walk down to the
destination,
 Unless kerb parking facility is adequately
designed in advance while planning a new
town, it might lead to a lot of
inconvenience to moving vehicles and
result in congestion at the road stretches
due to reduction in road capacity and
increase in accidents.

 Kerb parking facility may be either unrestricted
or restricted type,
 The restricted kerb parking may either be
controlled by police or by parking meters and
a specified parking fee is collected from those
who parking vehicles for a certain duration of
parking time.
 Different patterns of kerb parking are parallel
parking' shown in Fig 5.39 (a).
 The number of vehicles that can be parked per
unit length of the kerb are also shown in this
figure
Parallel parking
 Parallel parking need less roadway width, but
the number of vehicles that can be parked
per unit length of road is least as shown in
figure.
 Parallel parking is generally preferred when
the width of kerb parking space and the
width of the street are limited,
 But the parking and un-parking
operations are more difficult needing a
few forward and reverse movements before
parking properly or before taking out .
 Parallel parking may be either with equal
spacing facing the same direction or two
cars placed closely leaving a gap as open
space (for manoeuvring) between two-car
units

Angle parking
 Angle packing may be at angles 30, 45, 60 or 90 degrees
 The width of roadway required for parking and un-parking manoeuvres increase with
increase in parking angle up to a maximum at 90 degree angle.
 Angle parking accommodates more vehicles per unit length of kerb: maximum number
of vehicles that can be parked per unit length of the kerb is with right angle parking.
 Angle parking is more convenient to the drivers for the parking and un parking manoeuvres
than the parallel parking:
 However these cause much more obstruction to the through traffic resulting in more
accidents than the parallel parking.
 Out of various angles used for angle parking, 45 degree angle is considered the best taking into
account all the above factors.
OFF-STREET PARKING
Need for off-street parking
 At locations where the parking demand is high and kerb parking cannot be permitted in the
view of traffic congestion.
 off-street parking facilities are provided the nearest locations depending on the availability of
space for this purpose.
 When parking facility is provided at a separate place away from the road side or kerb. It is
known as 'off-street parking'.
 The main advantage of this method is that there is no undue increase in congestion, delay to
moving traffic due to on-street parking on the already congested roads.
 But the main drawback is some of the vehicle a users will have to walk a greater distance
after parking the vehicle at the off-street parking facility
 It is also not possible provide the off-street parking facility at very close intervals especially in
business centers of city

Types off street parking
 Two basic types of street parking facilities are surface parking lots and multi - floor
parking garages.
 Both in parking lots and the garages, the basic traffic operations consists of five steps
namely (i) entrance (ii) acceptance (iii) storage (iv) delivery v) exit.
 Hence some definite space is required and also for exit operations.
 This space provided is called 'reservoir area the size of which depends on the
average rate of arrival or vehicles to be parked during peak hour, the
average time required to dispose off' one car and the number of attendants
employed for storage-operations.
 However for self parking there is no need for the reservoir space, as the
additional space requirement at the entrance and exit will be minimum.
Surface parking lots
• Surface parking lots may be convenient where sufficient space is available at
comparatively low cost.
• When the parking of vehicles is done by owners or drivers of the cars, the
method is called 'self parking system'.
• If the vehicle is left by the driver at the entrance space and again collected
from there, the parking and delivering operations being earned out by
attendants, it is called 'attendant parking system'.
• Most important advantage of attendant parking is less space required to store
and manoeuvre the same number of cars.

Multi-storeyed parking garages
• Multi-storeyed parking garages are restored to when the floor space available for
parking garage: is less and is very costly.
• It is possible to construct multi-storeyed garages to park a large number of cars at a
time,
• The garages can be above the ground or below the ground or an integral of
both.
• It is necessary to provide the inter-floor travel facility for the vehicles, which may be
either by 'elevators' or by 'ramps'.
 In mechanized garages the elevator may be: designed to move both in vertical and in
horizontal directions to carry and place the vehicle in the appropriate parking
stall and to deliver it back
 The mechanized garages are operated by trained parking attendants only
 Therefore the owners/drivers of vehicles will have to hand over the vehicle and
the keys to the parking attendant at the reserved space at the entrance; similarly
the vehicle is taken delivery also from the space near the exit.
 One of the main advantages of mechanized parking garages is packing space
requirement is minimum and there is maximum utilization of available space.
 The disadvantage of this method is that if there is a mechanical break down or a
power failure the functioning of the elevator system would come to a stand-still.
• When ramps are provided for driving the vehicles to and from the parking stalls located at
different floor levels, the total space requirement will be increased considerably.
• For self parking the overall ramp space required will be still higher.

Terms related to the parking
Parking accumulation :
The total number of vehicles parked in an area at a specified moment.
The curve of parking accumulation for a typical day is given in fig 6.1
Parking volume:
The number of vehicles parking in a particular area over a given period of time.
It is usually measured in vehicles per day
Parking load –
The area under the parking accumulation curve during a specified period.
For example,
In fig 6.1, the hatched area represents the parking load in vehicle hour for a period of 4
hours from 6 a.mto 10 a.m
Parking duration – the length of time spent in parking space
Parking index – percentage of parking bays actually occupied by parked vehicles as
compared to the theoretical number available
Index = (number of bays occupied/ theoretical number of bays available )* 100
Parking turn over
Rate of the usage of the available parking space.
Thus
if there were 10 parking spaces used by 100 vehicles in a period of say 12 hours, then
parking turn over would be = 100/10 vehicles per space in a period of 12hr

ACCIDENT STUDIES AND ANALYSIS
Importance of accident studies
• The problem of accident is very acute in road transportation due to:
(i) complex flow patterns of vehicular traffic
(ii) presence of mixed type of vehicles and
(iii) the pedestrians on the roads.
• Traffic accidents may involve property damages, personal injuries and also deaths.
• One of the main objectives of traffic engineering is to provide safe traffic movements.
• The accident studies pertain to the road accidents that occur from time to time on an
existing road system.
• Though road accidents cannot be totally prevented, the accident rate can be decreased
substantially by suitable traffic engineering and management measures.
• It is essential to analyze every individual accident and to maintain zone-wise
accident records.
• The statistical analysis of accidents-carried out periodically at critical locations or
road stretches or zones or a city will help to arrive at suitable measures to effectively
decrease the accident rates.

The various objectives of the accident studies may be listed as:
(a) to study the causes of accidents and to suggest corrective treatment at potential
locations
(b) to evaluate existing design, regulation and control measures
(c) to support proposed changes in design, regulation and 'control measures in the
selected zone
(d) to carry out 'before and after studies' after implementing changes and to
demonstrate the improvement in the accident problem
(e) to make computations of financial loss due to accidents and
(f) to provide economic justification for the improvement measures suggested by the
traffic engineer
CAUSES OF ACCIDENTS
There are five basic elements in a traffic accident, namely:
• (a) Road user (b) Vehicle (c) Road and its condition (d) Traffic (e) Environmental
factors such as weather, visibility, etc.
• The road user responsible for the accident may be the driver of one or more
vehicles involved, pedestrians or the passengers.
• Vehicles involved in the accident may also be defective.
• The condition of the road surface or other existing geometric features or any of the
environmental conditions of the road may not be up to the expectation resulting in
accidents.
• The traffic flow and their characteristics could also cause undue strain on the
driver.
• Hence it is often not possible to pin point a particular single cause of an accident

.
Various causes of accidents may be listed a given below
(a) Drivers: Excessive speed and rash driving, carelessness, violation of rules and regulations,
failure to see or understand the traffic situation, sign or signal, temporary effects due to
fatigue, sleep or effect of consuming alcohol
(b) Pedestrians: Violating 'regulations, carelessness white using the carriageway meant for
vehicular traffic
(c) Passengers: Alighting from or getting into moving vehicles
(d) Vehicle defects: Failure of brakes, steering system, or lighting system, tier -burst and any
other defect in the vehicles
(e) Road condition: Slippery or skidding road surface, pot holes, ruts and other damaged
conditions of the road surface, temporary obstruction to line of sight (caused by branch of
tree or disabled vehicle) resulting in reduction in normal sight distance
(f) Road design: Defective geometric design like inadequate sight distance at horizontal or
vertical curves, improper curve design, inadequate width of shoulders, improper lighting
and improper traffic control devices
(g) Traffic condition: Other vehicles of the traffic stream, such as a vehicle moving ahead
getting involved in accident, presence of disabled vehicle on the roadway
(h) Weather: Unfavorable weather condition like mist, fog, snow, dust, smoke or heavy
rainfall which restrict normal visibility and render driving unsafe
(i) Animals: Stay animals on the road
(j) Other causes: Incorrect signs or signals, gate of level crossing not closed when required,
ribbon development, badly located advertisement boards or service station, etc.

Preventive measures of accidents ( Engineering measures , enforcement, education )
(i) ENGINEERING
Road design
 The geometric design features of the road such as sight distances, width of pavement,
and width of shoulders, horizontal and vertical alignment design details and intersection
design elements are checked and corrected if necessary.
 The pavement surface characteristics including the skid resistance values are
checked and suitable maintenance steps taken to bring them up to the design standards.
 Where necessary lay-passes may be constructed to separate through traffic from local
traffic.
 To minimize delay and conflicts at the intersections, it may be essential to design and
construct grade separated intersections or flyovers with interchange facilities.
Preventive maintenance of vehicles
• The braking system, steering, indicators, lighting system and condition of tires of vehicles
plying on the roads are to be checked at suitable intervals and heavy penalties levied
on defective vehicles.
• These measures are particularly necessary for public carriers.

(c) Before and after studies
 The record of accidents and their patterns for different locations are maintained by
means of collision and condition diagrams.
 After making the necessary improvements in engineering design, regulations,
enforcements and educational drives (covered under the '3-Es'), it is again necessary to
collect and maintain the record of accidents.
 The accident record supplemented with collision and condition diagrams during the
past two or three years are compared with similar data collected after implementing the
improvement measures for the identical duration.
 Such studies are called 'before and after studies' in order to compare the reduction in
accident rate, if any and the effectiveness of different preventive measures introduced.
(d) Road lighting
• Proper road lighting cap decrease the rate of accidents due to poor visibility during
night.
• Lighting is particularly desirable at intersections, bridge sites and at places were there
are restrictions to traffic movements

Enforcement measures
• The various measures of enforcement that may be useful to prevent accidents at spots
prone to accidents are enumerated here. The motor vehicle rules are revised from time
to time to make them more comprehensive.
(a) Speed control
The measures that can be taken to control the speed are by:
(i) Installation of speed limit and warning signs at all critical locations of the roads
(ii) Checking over speeding of vehicles by conducting surprise speed checks and levying
of fines and/or taking legal action on drivers who violate speed limits
(iii) Installation of tachometers in all public transport vehicles to give record of running
speeds and the respective timings; this will help the drivers of these vehicles to develop
the correct speed habit
(iv) Introduction of 'speed breakers' for control of vehicular speeds at the intersection of
minor roads with major roads; such speed humps may also be installed at identified
locations of local streets of residential areas, educational campuses, hospital area, market
area, etc.
• These speed breakers should be designed and located as per the IRC Guidelines.
• The speed breaker humps should be provided across the full width of the roadway
• They are formed along the roadway by providing a raised platform of height 100 mm
and length 2.0 m with ramps of length 1.5 m on either end of the platform;
• The intersection of edges of the raised platform and the ramps are rounded off by a
curve of radius 17 m

(b) Traffic control devices
 Existing signals may be re-designed or new signals introduced if necessary at un-controlled
intersections.
 Similarly proper traffic control device like speed limit signs, warning signs, markings or
channelizing islands may be installed wherever found necessary
(c) Training and supervision
• The transport authorities should be strict investigating and issuing license to drivers of
public service vehicles and taxis.
• Even the drivers who have passed the requisite: tests should be kept under proper
supervision and be trained in proper defensive driving.
• Driving license of the driver may be renewed after specified period, only after conducting
same tests to check whether the driver continues to be fit in all respects
(d) Medical check:
• The drivers should be tested for vision, glare recovery time and reaction time at prescribed
intervals, say once in three years
(e) Special precautions for commercial vehicles:
• It may be insisted on having a conductor or attendant to help and give proper direction to
drivers of heavy commercial vehicles and buses ' .
(f) Observance of law and regulation:
• Traffic or transport authorities should send study groups of trained persons, assisted by
police to different locations to check whether the traffic regulations are being followed by
the road users and also to enforce the essential regulations.
• The study group can provide useful data for deciding about the necessity of revision of
certain traffic regulations

(iii) Educational measures
(a) Education of road users
• The passengers and pedestrians should be taught the rules of the road, correct manner
of crossing etc.
• This may be possible by introducing necessary instruction in the schools for the
children.
• Posters exhibiting the serious results due to carelessness of road users may also be
useful.
• The Indian Roads Congress has published Highway Safety Co & and the documents on
Road Safety for school children and Instruction Manual on Road Safety Education
(b) Safety drive
• Organizing 'traffic safety week' when the road users are properly directed by the help of
traffic police
• Roads users should be impressed on what should and what should not be done, with
the, help of films and documentaries.
• Training courses may be conducted for drivers.
• Various institutions/organizations/departments have been organizing Highway Safety
Workshops in different regions of the country

ACCIDENT STUDIES AND RECORDS
The various steps involved in traffic accident studies are,
(i) collection of accident data
(ii) preparation of accident reports
(iii) preparation of location file
(iv) preparation of diagrams showing the type of collision and
(v) application of the above records for suggesting measures to prevent similar accidents
at the same location.
(i) Collection of accident data
• Collection of accident data is the first step in the accident study.
• Standard form for collecting the data has been suggested by the Indian Roads
Congress IRC: 53-1982. The details to be collected are briefly mentioned under:
(a) General - date, time, persons involved in the accident and their particulars,
classification of accident like fatal, serious, minor, property damage only, etc
(b) Location - description and details of the location of accident supported by diagrams
(c) Details of vehicles involved - registration number, make and description of the
vehicles, loading details, vehicular defects
d) Nature of accident – condition of vehicles involved, details of collision, and pedestrians or
objects involved, damages, injuries, casualty, etc
(e) Road condition - details of road geometries, whether the road stretch is straight or curved,
surface characteristics such as dry, wet or slippery, etc
( (f) Traffic condition - type Vehicles in the traffic flow, traffic volume and density, etc "

(g) Primary causes of accident - various possibly causes and the primary cause of the
accident
(h) Other probable causes/secondary and contributing causes for the accident
(i) Accident cost - the total cost of the accident such as property damages, personal injuries
computed in terms of Rupees
ACCIDENT REPORT
• The accident should be reported so police authorities who would further collect
required details and take legal action especially' in more serious accidents involving
injuries, casualties or severe damage to property.
• Accident report of the individuals involved may be separately taken.
• The accident data should be collected as given above and the accident report is
prepared with all facts which might be useful in subsequent analysis, claims for
compensation, evaluation of accident cost, etc.
ACCIDENT RECORDS
• Accident records are maintained giving all particulars of the accidents, location
other details.
• The records may be maintained by means of location files, spot maps, collision
diagrams and condition diagrams as given below.
(a) Location files
• These are useful to keep a record of the locations where accidents have taken place
within the concerned zone and to identify the locations of high accident incidence.
• Location files should be maintained by each police station for the respective
jurisdiction

(b) spot maps
• Accident location spot maps show - accidents by spots, pins or symbols on the road map of
the locality.
• A map of suitable scale, say 1 mm = 4 to 6 m, may be used for the preparation of spot
maps of urban accidents.
(c) collision diagram
• These diagrams depict the details of the accident location (not drawn to scale) and show
the approximate path of the vehicles and pedestrians involved in the accident and also
other objects with which the vehicles have collided.
• Collision diagrams are most useful to compare the accident pattern before and after the
remedial measures have been taken.
• A typical collision diagram and symbols used are shown in Fig. 18.3
Condition diagram
• A condition diagram is a drawing of the accident location drawn to scale, showing all the
important physical features of the road and adjoining area.
• The important features generally to be shown in the condition diagram with their
dimensions marked there-in are: the width of roadway, shoulders, median if any other
geometric details such as curves, kerb lines, bridges, culverts, electric posts, trees and
• all details of roadway conditions, obstruction to vision, property lines, signs, signals, etc.
• Standard symbols are used in showing various details.
• The condition and collision diagrams may be combined together in a single sketch, if
necessary
• A typical condition diagram and symbols used are shown in Fig. 18.5

Relief to accident victims
• The most essential and urgent requirement is to provide first aid and other medical
assistance to the injured as quickly as possible.
• It is also essential to arrange to transport the seriously injured persons to the nearest
hospital with appropriate facilities.
• Therefore it is desirable that an ambulance equipped with emergency treatment
facilities should reach the accident spot as quickly as possible along with a duty
doctor and supporting staff who could take care of the accident victims.

TRAFFIC VOLUME STUDIES
 Traffic volume or flow Traffic volume is a measure to quantify the traffic flow
 Different classes of vehicles make use of the same roadway, particularly in developing
countries like India; thus the traffic streams consist of 'mixed traffic flow.
 The vehicles of the traffic stream may be classified into different vehicle classes.
 They consist of: (i) fast moving vehicles such as (a) passenger cars, (b) buses, (c)
trucks or heavy commercial vehicles (d) light commercial vehicles - (LCV), (e) auto-
rickshaws-, (f) two-wheeler automobiles (motor cycles and scooters) and (ii) slow
moving vehicles such as animal drawn vehicles like bullock carts, cycle rickshaws,
pedal cycle, etc.
 Determination of the volume of each vehicle class separately and finding the total
volume is called 'classified traffic volume studies'.
• In order to express the total traffic flow on a road per unit time, it becomes necessary
to convert the flow of different vehicle classes into one standard vehicle type, such as
the 'passenger car'.
• Therefore each vehicle class is assigned an equivalency factor, called 'passenger car
unit' (PCU) in terms of a standard passenger car.
 A comprehensive traffic volume study includes the classified traffic counts of the
different vehicle classes per unit time and recording the direction-wise flow of each
vehicle class and pedestrian details also.

TRAFFIC VOLUME CHARACTERISTICS
 The traffic volume or the traffic flow is dynamic and varies from time to time.
 If a true picture of traffic flow on a road is to be obtained, the classified traffic volume
study should be conducted continuously by recording the direction-wise counts of
each vehicle class at selected time intervals (such as 10 or 15 minute intervals).
 From these data it is possible to obtain the hourly, daily and seasonal variations in
traffic flow and find the fluctuations and patterns of traffic flow.
 These details can be collected by establishing permanent traffic count stations and
recording of traffic flow continuously.
• An understanding of the traffic volume characteristics with the following details will
help in planning a new road project or for up-grading existing road facilities and for
effective management of traffic:
(a) Variation in volume during different hours of the day
(b) average volume during different days of the week
(c) average volume per day during different seasons of the year
(d) variation in traffic volume on different lanes
(e) directional distribution of traffic during different time periods and
(f) annual average daily traffic (AADT)

OBJECTS OF TRAFFIC VOLUME THE STUDIES
(a) To decide the priority for improvement and up-gradation of roads
(b) Re-design of roadway facilities
(c) For analysis of traffic patterns, rate of growth of each vehicle class and projecting
future traffic volume along identified roads
(d) For computing roadway capacity
(e) To plan traffic operation and control of existing facilities
(f) For planning one-way streets and other regulatory measures
(g) To plan and design new facilities
(h) Turning movement studies at intersections are used for introducing traffic control
devices, design or re-design of the signal timings
(i) At identified intersections are useful to assess the need for new grade separated
facilities
(j) For structural design/strengthening of pavements.
PEDESTRIAN VOLUME STUDIES
• Apart from the vehicular traffic, pedestrians also form part of the road users.
• Therefore pedestrian volume studies are required to plan and design separate
pedestrian facilities.
• Pedestrian traffic volume data are used for planning side-walks, cross-walks,
subways, foot-over-bridges and pedestrian signals.

METHODS OF CLASSIFIED TRAFFIC VOLUME STUDIES
Traffic volume counts may be carried out either manually or by using mechanical or
automatic counters.
MANUAL COUNTS
• This method employs a field team of enumerators at pre-determined locations of the
selected roads and intersections.
• The enumerator’s carryout classified count of the vehicles and record them on the
prescribed record sheets/fortes at desired time intervals.
• By this method, it is possible to obtain all the details of the classified traffic data
which cannot be collected by mechanical or other automatic counters. '
• It is possible to obtain details such as:
(i) Classification of different types of vehicles and their counts at desired time
intervals
(ii) Noting the direction-wise movements including turning movements of each
vehicle class at intersections
(iii) Classified vehicle counts with number of occupants in each passenger vehicle
(iv) Number of commercial vehicles (HCV and LCV) with details of load and the type
of commodity transported and
(v) Desired details of pedestrian volume counts.
• First the variations in hourly traffic volume during the 24 hours of the day
• The daily variations during different days of the week are to be observed.
• Also average 'daily traffic volume during different seasons of the year is to be noted.
• Then by statistical analysis, the peak hourly traffic volumes as well as the average
daily traffic volumes are calculated.

DISADVANTAGE
 It is not practicable to carry out manual count of different vehicle classes during all
the 24 hours of the day and all the days round the year.
 Hence it is necessary to adopt statistical sampling techniques and resort to 'short
counts‘ to save the time and work
AUTOMATIC TRAFFIC COUNTERS-CUM-CLASSIFIERS
• These may be either fixed or permanent type or portable type of counters.
• The mechanical counter can automatically record the total number of vehicles
crossing a section of the road in a desired period.
• One of the old methods of automatic counter is by the effect of impulses on a
pneumatic hose placed across the roadway;
• Traffic count is recorded by electrically operated counters and recorders capable of
recording the impulses;
• These are electronically recorded in computers to obtain classified vehicle counts
during desired time intervals.
• In addition, the lane occupancy and the speeds of different vehicles can also be
recorded.
• Weigh-in-Motion (WIM) systems will get additional data on the magnitude of loads
carried on different Axles.
• This information along with classified traffic volume data will help in projection of
traffic and in the design of pavements
• However, it is possible to classify and group the different types of vehicle % based
on axle spacing, axle loads, speed, height of vehicle, etc.

ADVANTAGE
• The main advantage of automatic traffic counter is that it can work throughout the
day and night for the desired period, recording the exact time at which each vehicle
crosses the line such as hourly volume, daily volume, etc
• It may not be practicable to collect such continuous counts for long durations by
manual counting method.
DISADVANTAGE
 But the impulses caused by vehicles of light weight may not be enough.
 The main drawback of the automatic counter is the it is not possible to classify and
record every vehicle type and get the details of turning movements, vehicle
occupancy, type of commodity transported by the commercial vehicles, etc.
 It is also not possible to record details of pedestrian flow.
TRAFFIC VOLUME COUNT AT MID – BLOCK INTERSECTIONS
• The intersection volume count consists of counting the number of vehicles entering
from each approach leg of the intersection at a fixed time intervals of say, 5, 10 or 15
minutes.
• The traffic flow diagram showing the total number of vehicles entering an,
intersection (typical cross roads with four legs) and the details of turning movements
are presented in Fig. 5.2.
• Apart from these, the occupancy of different vehicles, the number of pedestrians
walking along each leg of the intersection and crossing the road are also counted and
recorded by manual method

• The data on turning movements of different
vehicle classes are required for the design of
signal timings or to justify the need for grade
separated intersection.
• The data on queue length and delay at the
intersection, occupancy of different vehicle types
can be used in the economic analysis of
intersection improvement proposals.
 Pedestrian volume counts will help in the design
of side-walks and in deciding suitable facilities
for pedestrian crossing, including the timing of
signalized intersection.
 The traffic volume studies at the intersections
are conducted including peak and off-peak
periods

PRESENTATION OF TRAFFIC VOLUME DATA
• The data collected during the traffic volume studies are processed and are presented in
any of the following forms depending upon: the requirements.
ANNUAL AVERAGE DAILY TRAFFIC ( AADT )
• It is obtained by determining average daily traffic volume recorded for all 365 days of
the year.
• This data is useful in deciding the relative importance of a route and in phasing the
road development programme, determining the growth rate of different vehicle
classes.
AVERAGE DAILY TRAFFIC ( ADT )
• When the traffic volume counts are carried out only for a few days (such as for 3 to 7
days) the average daily traffic volume obtained is called `average daily traffic' or ADT.
• Traffic census on non-urban roads are generally carried out twice in a year by taking
direction-wise counts for 7-days period,
- once during the peak traffic season
- once during the lean season.
• In addition, the details of waiting time or delay at the intersection, the queue length
and 'the direction of turning movement may be noted.

TREND CHARTS
• Trend charts showing volume trends over period of years are prepared.
• These data are useful for estimating the rate of growth and for planning future
expansion, design and regulation.
VARIATION CHARTS
• Variation charts showing hourly, daily and seasonal variations are prepared.
• These help in deciding the facilities and regulation needed during peak traffic
periods.
TRAFFIC FLOW MAPS
• Traffic flow maps along the routes, (the thickness of the lines representing the traffic
volume to any desired scale), are drawn.
• These help to find the traffic volume distribution along the existing roads, at a
glance.
VOLUME FLOW DIAGRAM AT INTERSECTIONS
• Volume flow diagram at intersections either drawn to a certain scale or indicating
traffic volume (in numbers or in PCU) as shown in Fig. 5.2 are prepared, thus
showing the details of crossing and turning traffic.
• These data are needed for intersection design.

TRAFFIC VOLUME
DESIGN HOURLY TRAFFIC VOLUME
 Design hourly traffic volume is determined from the plot between hourly volume and
the number of hours in a year that the traffic volume is exceeded at desired location of
road. See Fig. 5.3.
 The highest or peak hourly volume of the year will be too high that it will not be
economical to design the facilities according to this volume.
 The annual average hourly volume (AAHV) found from AADT will not at all be
sufficient, because during considerable period of the year there will be severe
congestion.
 The design practice in the USA is to adopt a design hourly traffic-volume between 10th
and 50th highest hourly volume of the year.
 'Thirtieth highest hourly traffic volume' is the hourly volume that will be reached
only thirty times or exceeded only 29 times in a year and all other hourly volumes of
the year will be less than this value.
 The highway facilities designed with capacity for 30th highest hourly traffic volume in
the assumed year is found to be satisfactory from the consideration of facility as well
as the cost.
 This is because the cost will be much lesser when compared to the peak hourly
volume and there will be congestion, only during 29 hours in the year and this is
considered reasonable:
 Thus the 30th highest hourly volume is generally taken as the 'design hourly volume:
for the purpose of design of the roadway facility.

Estimate the theoretical capacity of a traffic lane with one way traffic flow at a stream speed of 40 kmph. Assume
the average space gap between vehicles to follow the relation S(g) = V*t where V- is the stream speed in kmph, t
is the average reaction time = 0.7 sec, assume average length of vehicles = 5.0 m.
Solution
Given: Stream speed, V = 40 kmph;
reaction time, t = 0.7 sec,
average length, L = 5.0 m
S (g) = (0.278 *V *t )+ L = (0.278 x 40 x 0.7) + 5.0 = 12.78 m
Theoretical capacity,
vehicles/hour/lane

PASSENGER CAR UNITS
MIXED TRAFFIC FLOW AND RELATED ISSUES.
• Different classes of vehicles such as cars, vans, buses, trucks, auto rickshaws, motor cycles, pedal
cycles, bullock carts, etc. are found to use the common roadway facilities without segregation on
most of the roads in developing countries like India.
• The flow of traffic with unrestricted mixing of different vehicle classes on the roadways forms the
heterogeneous traffic flow or the 'mixed traffic flow'.
• The different vehicle classes have a wide range of static characteristics such as length, width, etc.
and dynamic characteristics such as speed, acceleration, braking characteristics; etc.
• Apart from these, the driver behavior of the different vehicle classes is also found to vary
considerably.
• Therefore the mixed traffic flow characteristics are very much complex when compared to
homogeneous traffic consisting of passenger cars only.
OBJECTS OF EQUIVALENCY FACTORS TO REPRESENT MIXED TRAFFIC VOLUME
• It is rather difficult to estimate the traffic volume of roadway facilities under mixed traffic flow,
unless the different vehicle classes are converted to one common standard vehicle unit.
• Therefore it is necessary to determine or to assign equivalency factors for different classes of
vehicles.
• It is a common practice to consider the passenger car as the standard vehicle unit to convert the
other vehicle classes and this unit is called 'Passenger Car Unit' or PCU'.
• The total traffic volume of the mixed traffic flow prevalent on the roads in India is generally
expressed in terms of PCU per hour or PCU/lane/hour and the traffic density as PCU per
kilometer length of lane.

CONCEPT OF PCU VALUE
 The pcu may be considered as a measure of relative space requirement of a
vehicle class compared to that of passenger car under a specified set of
roadway.
 If the addition of one vehicle of a particular class in the traffic stream
produces the same effect as that due to addition of one passenger car, then that
vehicle class is considered equivalent to the passenger car with a pcu value equal
to 1.0.
FACTORS AFFECTING PCU VALUES
(a) Dimensions of vehicles such as width and length
(b)Dynamic characteristics of vehicles such as power, speed, acceleration and
braking
(c) Transverse and longitudinal gaps or clearances between moving vehicles
(d)Traffic stream characteristics such as composition of different vehicle classes
mean speed and speed distribution of mixed traffic stream
(e) Roadway characteristics such as road geometrics including gradient and
curves, access controls, rural or urban, presence of intersections and the type
of intersections
(f) Regulation and control of traffic such as speed limit, one way traffic, etc
(g) Environmental and climatic conditions

DEFINITION OF THE STUDY AREA
 The study area for which transportation facilities are being planned is first of all defined.
 Transportation planning can be at the national level, the regional level or at the urban level.
 For planning at the urban level, the study area should embrace the whole conurbation
containing the existing and potential continuously built-up areas of the city.
 The imaginary line representing the boundary of the study area is termed as the 'external
cordon'.
 The area inside the external cordon line determines the travel pattern to a large extent and as
such is surveyed in great detail.
 The land-use pattern and the economic activities are studied intensively and detailed surveys
(such as the home interview) are conducted in this area to determine the travel characteristics.
 On the other hand, the area outside the external cordon line is studied to a lesser degree of detail.
The selection of the external cordon line for an urban transportation study should be
done carefully with due weightage to the following factors
(i)The external cordon line should circumscribe all areas which are already built-up and those areas
which are considered likely to be developed during the period of study.
(ii) The external cordon line should contain all areas of systematic daily life of the people oriented
towards the city center and should in effect be the 'commuter-shed'.
(iii)The external cordon line should be continuous and uniform in its course so that movements
cross it only once.
- The line should intersect roads where it is safe and convenient to carry out traffic surveys.
(iv)The external cordon line should be compatible with previous studies of the area of studies
planned for the future.

Home-Interview Surveys
 The information on travel pattern includes number of trips made, their origin and
destination, purpose of trip, travel mode, time of departure from origin and time of
arrival at destination and so on.
 The information on household characteristics includes type of dwelling unit, number of
residents, age, sex, race, vehicle ownership, number of drivers, family income and so
on.
 Based on these data it is possible to relate the amount of travel to household and zonal
characteristics and develop equations for trip generation rates.
 Because of the wide variety of data that can be collected by the home-interview
technique and the high cost involved, it is necessary to standardize the procedure for
such surveys.
 It is impractical and unnecessary to interview all the residents of the study area.
 Since travel patterns tend to be uniform in a particular zone, it is sufficient if a sampling
procedure is employed.
 The size of the sample is usually determined on the basis of the population of the
study area, and the standards given in Table 30-1 of the Bureau of Public Roads (B.P.R.)
are often used.

 The full-interview technique involves interviewing as many members of the household as possible
and directly recording all the information.
 In the home questionnaire technique, the interviewer-collects only details of the household
characteristics, leaving forms for household residents to complete in regard: to travel information.
 The completed forms are collected by the interviewer after a day or two.
 In both the above methods, it is necessary to send out a letter proposed to the selected households
prior to the proposed interview, explaining the nature, importance and objectives of the survey
and eliciting their co-operation.
 In addition, wide publicity is given to the survey in the local press, radio and television.

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