traffic study report
TRANSCRIPT
1
CHAPTER ONE: INTRODUCTION
TRAFFIC STUDIES
Traffic studies are conducted to analyse the traffic characteristics. These studies are useful in design
and maintenance of traffic features. Traffic studies or surveys for collecting traffic data are also called
traffic census. The various traffic studies generally conducted are:
a. Traffic volume study
b. Traffic flow characteristics
c. Traffic capacity studies
d. Parking studies
e. Speed studies
i. Spot speed study
ii. Speed and delay study
f. Accident study
The kind of traffic study being reported here is speed study. Emphasis would be laid on this aspect of
traffic study.
SPEED
Speed is literally the total distance travelled divided by the time of travel. It is expressed in metric units
of kilometres per hour. The reciprocal of speed, travel time, is usually expressed in units of minutes per
km.
There are three basic measures of speeds of travel.
1. Spot speed
This is the instantaneous speed of a vehicle as it passes a specified point along a roadway. The
average of a series of measures of speed can be expressed in two ways: the space-mean speed
and the time-mean speed.
I. Space-mean speed (��)
This is the harmonic mean of speeds passing a point during at an instance.
�� = �
∑ ������
��
Where �� = observed speed of the ith vehicle
2
n = total number of vehicles observed
It can also be defined as the average speeds of vehicles over a relatively long section of
roadway.
If �� = � ���
where � = distance of roadway section
�� = observed time for the ith vehicle to travel distance �
1 ��� = � ��
� ��
1��
� = ���.��
���
Hence, �� = �.���∑ ��
��= 1
The average travel time of all the vehicles is obtained from the reciprocal of the space-
mean speed.
II. Time-mean speed (��)
This is the arithmetic mean of the speeds of the vehicles passing a point.
�� = ��
∑ ����
Space-mean speed and time-mean speed are not equal. In fact, it has been established
that
�� = �� + ���
��
Where ��� = variance of the speed distribution of speeds.
2. Running speed
This is the total distance covered divided by the time the vehicle is in motion. The time when
the vehicle is in motion is known as the running time. This excludes delays and stoppages.
3. Overall travel (journey) speed
This is the total distance travelled divided by the total time taken including delays and
stoppages enroute.
3
Factors affecting spot speeds
1. Time: time has a significant effect on spot speed. Generally, higher speeds are obtained in the
morning when people are trying to get to their various places of work.
2. Traffic condition: speeds of vehicles decrease with increase in number of vehicles on a
roadway. Accidents along a roadway would also slow down the speeds of vehicles along that
roadway.
3. Geometric features: a driver would tend to slow down the speed of his vehicle when
approaching a curve or intersection.
4. Location: speeds on rural highways are higher than those on urban highways. This is so
because there are fewer cars on rural roads. Also, drivers tend to reduce the speeds of their
vehicles when close to an educational institution e.g. school.
5. Environmental conditions: rain, wind.
Methods of measuring spot speeds
Pressure Contact Tubes
Detectors (usually pneumatic tubes) are used to indicate the entering and leaving the base length. When
a vehicle passes over the tube laid at the first reference point, an air impulse is sent, which activates an
electromagnetically controlled stop-watch in the lands of the observer. When the vehicle passes over the
second tube, the stop-watch automatically stops. The reading is noted by an observer. Alternatively, the
readings can be recorded by automatic data recorder.
Radar speed meters
These meters work on the Doppler principle that the speed of a moving body is proportional to the
change in the frequency between the radio wave transmitted to the moving body and the radio wave
received back. The instrument directly measures the speed, and an accuracy of at least ± 1.5 to 3 kmph is
possible.
Photographic Method and Video Camera Method
In this method, photographs are taken at fixed intervals of time (say one second per frame) on a special
camera. By projecting the film on the screen, the passage of any vehicle can be traced with reference to
time. Images by video camera can also be used.
4
Direct- Timing method for spot speed determination
Two reference points are marked on the pavement at a suitable distance apart and an observer starts
and stops an accurate stop-watch as a vehicle crosses the two marks. From the known distance and the
measured time intervals, speeds are calculated.
Enoscope
This device, also known as the Mirror-box, is an L-shaped box, open at both ends, with a mirror set at a
45-degree angle to the arms of the instrument. The instrument bends the line of sight of the observer so
that it is perpendicular to the path of the vehicle. 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. The method can be used with
one enoscope or with two enoscopes.
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CHAPTER TWO: METHODOLOGY
This is an account of how the speed study was carried out.
• Location: between Tipper Garage and Tanke Junction, Ilorin.
• Number of individuals involved : Two(2)
• Period of study: between 7 a.m. and 9 a.m. on a weekday (Thursday).
• Instruments used: stop-watch, measuring tape, marker chalk), data sheet/book.
PROCEDURE
• Two reference points were taken and measuring tape was used to measure the distance between
the points.
• Chalk was used to mark the two points. The two observers were stationed at these points.
• An observer stood at the reference point where the vehicle passed first (from Tipper Garage),
signalled every time a vehicle to be timed passed that point. Then the second observer would
afterwards start the stop-watch.
• The second observer would then stop the stop-watch whenever he observed the same vehicle
pass the reference point.
• The distance apart and the time taken for each vehicle to cover the distance were used to
calculate the speed of each vehicle.
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CHAPTER THREE: COMPUTATION AND ANALYSIS
The data sheet used for the study is as shown below.
DISTANCE, d = 27m
Vehicle no time in (t1) time out (t2)
7 a.m. – 8 a.m.
1 0.00 5.02
2 5.02 8.67
3 8.67 14.87
4 14.87 20.17
5 20.17 23.50
6 23.50 30.52
7 30.52 35.48
8 35.48 38.53
9 38.53 42.12
10 42.12 46.57
11 46.57 51.13
12 51.13 56.85
13 56.85 63.60
14 0.00 7.18
15 7.18 11.62
16 11.62 18.07
17 18.07 21.08
18 21.08 24.70
7
19 24.70 32.17
20 32.17 38.77
21 0.00 6.15
22 6.15 21.15
23 0.00 8.75
24 8.75 26.45
25 26.45 32.03
26 32.03 47.62
27 47.62 53.59
28 0.00 6.10
29 6.10 10.60
30 10.60 13.95
31 13.95 17.38
32 17.38 19.65
33 19.65 24.23
34 24.23 30.03
35 30.03 34.13
36 34.13 38.02
37 0.00 3.50
38 0.00 3.50
39 0.00 3.78
40 3.78 7.08
41 7.08 11.42
8
42 11.42 14.10
43 14.10 18.27
44 18.27 22.38
45 22.38 25.50
46 25.50 28.33
47 28.33 31.52
48 0.00 6.17
49 6.17 9.13
50 9.13 13.75
51 13.75 19.00
52 0.00 2.58
53 0.00 4.62
54 4.62 8.64
55 0.00 9.43
56 9.43 12.95
57 12.95 17.62
58 17.62 21.03
8 a.m. – 9 a.m.
59 0.00 3.33
60 3.33 6.62
61 6.62 10.02
62 10.02 14.58
63 14.58 19.58
9
64 0.00 03.20
65 3.20 6.72
66 6.72 11.28
67 11.28 17.08
68 0.00 5.60
69 5.60 12.10
70 12.10 20.27
71 0.00 11.50
72 11.50 23.07
73 0.00 7.23
74 7.23 12.73
75 12.73 22.45
76 22.45 27.38
77 27.38 35.27
78 0.00 6.23
79 0.00 7.38
80 7.38 25.22
81 25.22 32.33
82 0.00 9.08
83 9.08 17.92
84 17.92 22.15
85 0.00 4.55
86 4.55 9.28
10
87 9.28 16.58
88 0.00 5.42
89 5.42 9.62
90 9.62 14.20
91 0.00 5.78
92 5.78 17.18
93 17.18 26.35
94 0.00 4.63
95 4.63 7.53
96 7.53 13.18
97 13.18 19.17
98 0.00 5.08
99 5.08 9.33
100 9.33 13.75
101 13.75 17.83
102 17.83 22.65
11
The table below shows time and calculated speed.
DISTANCE, d = 27m
Vehicle no time, t (s) speed V, (m/s) V (km/hr)
7 a.m. – 8 a.m.
1 5.02 5.38 19.40
2 3.65 7.40 26.60
3 6.20 4.35 15.70
4 5.30 5.09 18.30
5 3.33 8.11 29.20
6 7.02 3.85 13.90
7 4.96 5.44 19.60
8 3.05 8.85 31.90
9 3.59 7.52 27.00
10 4.45 6.07 21.90
11 4.56 5.92 21.30
12 5.72 4.72 17.00
13 6.75 4.00 14.40
14 7.18 3.76 13.50
15 4.44 6.08 21.90
16 6.45 4.19 15.10
17 3.01 8.97 39.30
18 3.62 7.46 26.90
19 7.47 3.61 13.00
12
20 6.60 4.09 14.70
21 6.15 4.39 15.80
22 15.00 1.80 6.50
23 8.74 3.09 11.10
24 17.70 1.53 5.50
25 5.58 4.84 17.40
26 15.59 1.73 6.20
27 5.97 4.52 16.30
28 6.10 4.43 16.00
29 4.50 6.00 21.60
30 3.35 8.06 29.00
31 3.43 7.87 28.00
32 2.27 11.89 42.80
33 4.58 5.90 21.20
34 5.80 4.66 16.80
35 4.10 6.59 23.70
36 3.89 6.94 25.00
37 5.32 5.08 18.30
38 3.50 7.71 27.80
39 3.78 7.14 25.80
40 3.30 8.18 29.40
41 4.34 6.22 22.40
42 2.68 10.07 36.30
13
43 4.17 6.47 23.30
44 4.11 6.57 23.70
45 3.12 8.65 31.10
46 2.83 9.54 34.30
47 3.19 8.46 30.60
48 6.17 4.38 15.80
49 2.96 9.12 32.80
50 4.62 5.84 21.00
51 5.25 5.14 18.50
52 2.58 10.47 37.70
53 4.62 5.84 21.00
54 4.02 6.72 24.20
55 9.43 2.86 10.30
56 3.52 7.67 27.60
57 4.67 5.78 20.80
58 3.41 7.92 28.50
8 a.m. – 9 a.m.
59 3.33 8.11 29.20
60 3.29 8.21 29.60
61 3.40 7.94 28.60
62 4.56 5.92 21.30
63 5.00 5.40 19.40
64 3.20 8.44 30.40
14
65 3.52 7.67 27.60
66 4.56 5.92 21.30
67 5.80 4.66 16.80
68 5.60 4.82 17.40
69 6.50 4.15 14.90
70 8.17 3.30 11.90
71 11.50 2.35 8.50
72 11.57 2.33 8.40
73 7.23 3.73 13.40
74 5.50 4.91 17.80
75 9.72 2.78 10.00
76 4.93 5.48 19.70
77 7.89 3.42 12.30
78 6.23 4.33 15.60
79 7.38 3.66 13.20
80 17.84 1.51 5.40
81 7.11 3.80 13.70
82 9.08 2.97 10.70
83 8.84 3.05 11.00
84 4.23 6.38 23.00
85 4.55 5.93 21.30
86 4.73 5.71 20.60
87 7.30 3.70 13.30
15
88 5.42 4.98 17.90
89 4.20 6.43 23.10
90 4.58 5.90 21.20
91 5.78 4.67 16.80
92 11.40 2.37 8.50
93 9.17 2.04 10.60
94 4.63 5.83 21.00
95 2.90 9.31 33.50
96 5.65 4.78 17.20
97 5.99 4.51 16.20
98 5.08 5.31 19.10
99 4.25 6.35 22.90
100 4.42 6.11 22.00
101 4.08 6.62 23.80
102 4.82 5.60 20.20
Time, t = �� − ��
Speed, V = ��������,(�)��� �, (�)
� �⁄
V (km/hr) = V (m/s) × 3.6
16
Frequency Distribution of Spot Speed Data
Class speed limit (kmph)
Mid-point speed, V(kmph)
No of vehicles(f) Frequency (%)
Cumulative frequency (%)
0.00-4.90 2.45 0 0.00 0.00 5.00-9.90 7.45 7 6.86 6.86
10.00-14.90 12.45 18 17.65 24.51 15.00-19.90 17.45 25 24.51 49.02 20.00-24.90 22.45 25 24.51 73.53 25.00-29.90 27.45 16 15.69 89.21 30.00-34.90 32.45 7 6.86 96.08 35.00-39.90 37.45 3 2.94 99.02 40.00-44.90 42.45 1 0.98 100.00
Average speed, � = ∑ ��∑ �
= ����.�����
= 20.538≅ 21kmph/veh
Cumulative frequency curve
98th percentile speed = 35kmph
85th percentile speed = 25.8kmph≅ 26kmph
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45 50
Cum
. per
cent
of v
ehic
les o
bser
eved
Speed, V (kmph)
17
50th percentile speed = 17.5kmph≅ 18kmph
15th percentile speed = 10.3kmph≅ 10kmph
Frequency distribution curve of the spot speeds
Modal average = 20kmph
INFERENCE
1. The 98th percentile speed (here 35kmph) is used as the design speed in geometric design.
2. The 85th percentile speed (here 26kmph) is used for determining the speed limits for traffic
regulation.
3. The 50th percentile speed(here 18kmph) is the median speed and this is the speed at which there
are as many vehicles going faster as there are going slow.
4. The 15th percentile (here 10kmph) is used to determine the lower speed limits on major highway
facilities such as Expressways.
0
5
10
15
20
25
30
0 5 10 15 20 25 30 35 40 45 50
Perc
ent f
requ
ency
of v
ehic
les o
bser
ved
Speed, V (kmph)
18
CHAPTER FOUR
PROBLEMS ENCOUNTERED
Some of the problems encountered during the study are
1. Speed readings were influenced by the driver reaction due to conspicuousness of the observers.
2. Intermittent parking of vehicles caused distraction and hindered vision considerably.
3. Distraction from passers-by in a bid to inquire about what is going on.
APPLICATION OF SPEED STUDIES
1. Speed data is used for the analysis of road improvement schemes.
2. Spot speed studies are needed for the regulation and control of traffic operations. These include
location and size of traffic signals and establishment of safe speed limits.
3. Based on speed studies, the design speed can be selected, and other geometric elements of
design such as horizontal curvature, sight distances and super-elevation can be determined.
4. Problems relating to congestion on roads can be analysed and resolved with speed data.
5. Spot speed data are used in analysing the causes of accidents and relation between speed and
accidents.
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RECOMMENDATION
1. More methods of spot speed determination should be introduced to students of learning e.g. the
use of radar speed meter, enoscope and pressure contact tubes.
2. Students should be allowed to participate in traffic studies organized by the institution’s roadway
section. This would afford them the opportunity to get more familiar with traffic studies and
make them recognize its value.
CONCLUSION
Spot speed study is an important aspect of traffic census which helps in design and control of traffic
characteristics.
This traffic study imposed on students is a good one which will make them gain practical experience of
what they have been taught in class.
REFERENCES
1. Dr. S.K. Khanna and Dr. C.E.G. Justo. Highway Engineering.
2. Dr. L.R. Khadiyali. Traffic Engineering and Transport Planning.
3. www.wikipedia.com
4. www.tfhrc.gov/index.html