2.2_Traffic Studies_Speed Studies_045446.pptx

Department of Civil Engineering, NIT Srinagar
A presentation on
Presented By:
Dr. Jitendra Gurjar
Assistant Professor
1

 Speed is the ratio of the total distance (d) travelled by a vehic
le to the total time (t) taken by the same vehicle.
 Speed, V= (d/t) m/sec.
 The speed survey is done to determine the speed that drivers
select, unaffected by the existence of congestion.
 This information is used to determine general speed trends, t
o help determine reasonable speed limits, and assess safety.
 The speed of travel on the road is also used in classifying rou
tes.
The level of service based on speed is an indicator of the quality
of traffic flow or mobility.
2

 The speed of different vehicles varies with respect to time and s
pace.
 To represent, these variations several types of speed can be defin
ed. These are
 Spot speed
 Average speed
 Time Mean Speed (Vt)
 Space Mean Speed (Vs)
 Running speed
 Journey speed
3

 Spot speed is referred to as the instantaneous speed of a vehicle
at a point or cross-section.
4
 Spot speed is needed to design
 Horizontal and vertical curve
 Location and size of sign
 Accident analysis

 Spot speed is measured using an
 Pavement Marking Method
 Enoscope or Mirror Box Method,
 Radar Method
 Photographic Method
 Electronic Method
5

 Pavement Marking Method
 The pavement marking method can be used to successfully c
omplete a spot speed study using a small sample size taken o
ver a relatively short period of time.
 It is a quick and inexpensive method for collecting speed dat
a but a relatively inaccurate method.
 To calculate vehicle speed, we use the predetermined study l
ength known as trap length and the elapsed time it takes for t
he vehicle to move through the test section in the following f
ormula: V= (d/t) m/sec.
6

7
Traffic Stream Average
Speed (mile/hr)
Trap length
(feet)
Below 25 88-100
25-40 176-200
Over 40 264-300
 The pavement marking method can be used to successfully c
omplete a spot speed study using a small sample size taken o
ver a relatively short period of time.
 Marked the recommended study lengths on the pavement bas
ed on the average speed of the traffic stream.

8
 As the front of the vehicle crosses the s
tarting section of the study length, the s
tarting section observer sends a signal t
o the end section observer who starts th
e stopwatch.
 The end section observer stops the stop
watch when the vehicle reaches the end
station.

9
 Therefore, the time elapsed between
the two sections is obtained.
 Repeat the procedure for recording t
he time of vehicles moving in the op
posite direction.
 Calculate vehicle speeds by using th
e predetermined study length and the
elapsed time

 Enscope or Mirror Box Method
 Enoscope, also known as the Mirror Bo
x, is an L-shaped box, open at both ends
, with a mirror set at a 45° angle to the a
rms 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 method can
be used with one Enoscope or with two
Enoscopes. 11

12
Traffic Stream Average
Speed (mile/hr)
Trap length
(feet)
Below 25 88-100
25-40 176-200
Over 40 264-300
 Marked the recommended study lengths on the pavement b
ased on the average speed of the traffic stream.
 Enoscope is placed directly opposite to the first reference p
oint and the observer stands opposite to another reference p
oint such that the observer and Enoscope are in the same li
ne of sight.

13
 Start the stopwatch when the image of t
he passing vehicle is seen through the E
noscope by the observer and stop the st
opwatch as soon as it passes the observ
er.
 Therefore, the time elapsed is obtained.
 Repeat the procedure for recording the t
ime of vehicles moving in the opposite
direction.

14
 If two Enoscopes are used the
n the observer stands mid-way
between two reference points
and notes the time taken.
 Calculate vehicle speeds by us
ing the predetermined study le
ngth and the elapsed time.

 Speed Radar Gun Method
 The speed gun or radar meters are used f
or the measurement of spot speeds much
more rapidly as compared to previously d
iscussed methods.
 It measures speed directly by measuring t
he difference in the frequency between th
e emitted and reflected radar wave emitte
d on an oncoming vehicle.
15

 The principle of the radar
meter is that when it is tar
geted at a vehicle moving
with some speed, the diffe
rence between the frequen
cies of the emitted and ref
lected beams is used to ca
lculate the speed.
16

 This is normally referred to as th
e Doppler Effect which states tha
t the difference in frequency is pr
oportional to the speed of the onc
oming vehicle.
 Using this principle, the instrume
nt is programmed to calculate the
speed of the vehicle.
17

Advantages
 The radar speed meter is pre-calibrated to display/record th
e 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 r
equired for the measurement of speeds of cars during the ca
r- race.
18

Advantages
 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 handheld radars of small size are also available.
Disadvantage
 One of the disadvantages of this type of equipment is that whe
n more than one vehicle is trapped, the speed of the closest veh
icle only will be recorded.
19

Average Speed
It is the average spot speed of all vehicles passing a given point
on the road.
There are two types of average speeds
 Time-mean speed
 Space-mean speed
20

Time Mean Speed
Time mean speed is the average of all vehicles passing a point o
ver a duration of time.
It is the arithmetic mean of the speed of the vehicles passing a p
oint on a highway during an interval of time.
It represents the speed distribution of vehicles at a point on the r
oadway.
21

Time Mean Speed
Time mean speed Vt is given by
22
Where
n= number of vehicles observed
d= length of section of highway
Vi =Observed instantaneous speed of ith vehicles in kmph
qi is the number of vehicles in the ith speed range
vi mean speed of vehicles in the ith speed range

Space Mean Speed
The space mean speed also averages the spot speed, but spatial
weightage is given instead of temporal.
Space mean speed is the harmonic mean of the speed of the veh
icles passing a point at the highway during an interval of time.
This speed is used for flow density relationships.
23

Space Mean Speed
Consider the unit length of a road, and let vi is the spot speed of
ith vehicle. Let ti is the time the vehicle takes to complete the unit
distance and is given by
If there are n such vehicles, then the average travel time ts is giv
en by,
24

» Average Speed: Relationship between Time-mean speed and space-mean
Speed
where,
» vt = Time-mean speed
» vs = Space-mean speed
» σs = Standard deviation in space mean speed
» σt = Standard deviation in time mean speed
» vi = speed of ith vehicle
» qi = frequency of ith vehicle
25

Average Speed
The space-mean speed is slightly lower than the time-mean s
peed under typical speed conditions on rural highways.
26

Q.1 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, 6
5, 33, 69, 34, 51, 47, 41, 62, 43, 55, 40,
Calculate : (i) Time – mean speed (ii) space-mean speed and
27

Q.2 Speed observations from a
radar speed meter have been ta
ken, giving the speeds of the su
bsidiary streams composing the
flow along with the volume of t
raffic of each subsidiary stream
. The readings are as under:
Calculate (i) Time-mean speed
(ii) Space-mean speed (iii) Va
riance and standard deviation a
bout space-mean speed (iv) Var
iance and standard deviation ab
out time-mean speed
28
Speed
(km/hr)
Volume of subsidiary st
ream (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

Journey speed
It is the distance divided by the total journey time.
Total journey time includes all delays due to traffic.
Journey speed = Distance/Total journey time
29

Running speed
It is the ratio of the distance divided by running time.
Running time is the time that the vehicle is actually in motion i.
e. total journey time minus delays.
Running speed = Distance/(Total journey time – delays)
Both speeds are usually a result of travel time and delay study
– used to evaluate road performance.
30

Q.3 Evaluate journey & running speeds for the following situa
tion: Average Total travel time including delay due to tra
ffic = 32 minutes. Average Delays at each junction: J1 =
5 min, J2 = 5 min, J3 = 3 min, J4 = 4 min, and J5 = 6 mi
n.
31

Presentation of Spot Speed Data
From the spot speed data of the selected samples, a frequency d
istribution table of spot speed data is prepared by arranging the sp
eed groups covering desired speed ranges (such as 10 - 20 kmph,
20-30 kmph, 30-40 kmph, etc. ) and the number of vehicles in eac
h speed range.
The arithmetic mean of the measured speeds is taken as the aver
age spot speed of all the vehicles in the stream.
32

Presentation of Spot Speed Data
It is possible to determine either the average spot speed of any desi
red vehicle class (such as car, HCV, etc.) or the combined weighted a
verage speed of all the vehicles in the traffic stream.
The table gives the general information of the speeds maintained i
n the section and also regarding the speed distribution pattern.
33

Frequency Distribution D
iagram
A graph is plotted betwee
n the average values of eac
h speed group of vehicles o
n the X-axis and the percen
tage of vehicles in that grou
p on the Y-axis.
This graph is called the fr
equency distribution diagra
m of spot speeds.
34

Frequency Distribution Diagram: Model Speed
This diagram will have a definite peak value of travel speed acro
ss the section and this speed is denoted as 'modal speed'.
It may be inferred that the maximum proportion of vehicles in th
e stream prefers to travel at about this speed on this particular locat
ion of the road.
A vertical line is dropped from the peak of the curve, with the res
ult found on the horizontal axis.
35

Frequency Distribution Diagram: Model Speed
36

Frequency Distribution Diagram: Median Speed
The median speed is defined as the speed that divides the distrib
ution into equal parts (i.e., there are as many observations of speed
s higher than the median as there are lower than the median).
It is a positional value and is not affected by the absolute value o
f extreme observations.
37

Frequency Distribution Diagram: Median Speed
By definition, the median equally divides the distribution.
Therefore, 50% of all observed speeds should be less than the
median.
In the cumulative frequency curve, the 50th percentile speed is t
he median of the speed distribution. Median Speed = v50.
38

Frequency Distribution Diagram: Pace
The pace is a traffic engineering measure not commonly used
for other statistical analyses.
It is defined as the 10 km/h increment in speed in which the h
ighest percentage of drivers is observed.
It is also found graphically using the frequency distribution c
urve.
The pace is found as follows: A 10 kmph template is scaled fr
om the horizontal axis. 39

Frequency Distribution Diagram: Pace
Keeping this template horizontal, place an end on the low
er left side of the curve and move slowly along the curve.
When the right side of the template intersects the right sid
e of the curve, the pace has been located.
This procedure identifies the 10 Km/h increments that inte
rsect the peak of the curve; this contains the most area and, t
herefore, the highest percentage of vehicles.
40

Frequency Distribution Di
agram: Pace
41

'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 the figure.
This graph is called the 'cumulative speed distribution diagram
’
42

Frequency Distribution Diagram of Spot Speeds
43

Speed Dispersion
The ‘15th percentile speed’ means the speed at or below whi
ch 15 percent of the vehicles are passing the point on the highwa
y.
On some arterial roads where slow-moving vehicles are to be p
rohibited,15th percentile speed may be determined from the cumu
lative speed distribution diagram.
The 15th percentile speed is considered to represent the low
er speed limit, to prohibit slow-moving' vehicles to decrease dela
y and congestion.
44

Speed Dispersion
The ‘50th percentile speed’ means the speed at or below whi
ch 50 percent of the vehicles are passing the point on the highwa
y.
50th percentile speed may be determined from the cumulative s
peed distribution diagram.
The 50th percentile speed is considered to represent the mea
n speed.
45

'Cumulative Speed Distribution Diagram of Spot Speeds
The '85th percentile speed’ means the speed at or below which
85 percent of the vehicles are passing the point on the highway. In
other words, only 15 percent of the vehicles exceed this speed at t
hat spot.
The drivers exceeding 85th percentile speed are usually consider
ed to drive faster than the safe speed under existing conditions.
Hence this speed is adopted for the 'safe speed limit' at this zone.
46

Cumulative Speed Distribution Diagram
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,
A cumulative speed distribution diagram is plotted and an “85”
percentile speed is adopted as the upper-speed limit.
47

Cumulative Speed Distribution Diagram
Speed Dispersion
The ‘98th percentile speed’ means the speed at or below which
98 percent of the vehicles are passing the point on the highway.
For the purpose of checking the requirements of highway geometr
ic design elements, the 98th percentile speed is generally taken as t
he 'design speed' of the existing roadway facility.
48

Speed Dispersion
All vehicles do not travel at the same speed at a location on a r
oad.
If there is 'free flow of vehicles, the speed distribution generall
y follows a normal distribution curve.
The amount of spread of speeds from the average speed affects
both capacity and safety.
49

Speed Dispersion
This spread in speeds is represented by 'speed dispersion'.
The quality of the flow of vehicles in a traffic stream may be re
presented in terms, of speed dispersion.
The speed dispersion may be judged by several methods such a
s.
(a) 85th minus 15th percentile of spot speeds, (b) standard devi
ation of spot speeds, or (c) the coefficient of variation of spot spe
eds. 50

Q.4The table below gives the consolidated data of spot speed studies on a s
ection of a road. Determine the most preferred speed at which the maximu
m proportion of vehicles.
51
Speed Range
(km/hr)
No. of Speed
Observations
0-10 0
10-20 11
20-30 30
30-40 105
40-50 233
50-60 216
60-70 68
70-80 24
80-90 0

Q.5 Spot speed studies were
carried out at a certain stretch
of a highway with mixed traf
fic flow and the consolidated
data collected are given belo
w. Determine:
(i) The upper and lower value
s or speed limits for installing
speed regulation signs at thi
s road stretch, (ii) The desi
gn speed for checking the
geometric design elements o
f the highway, and (iii) Speed
dispersion
52
Speed Range
(km/hr)
No. of Speed
Observations
0-10 12
10-20 18
20-30 68
30-40 89
40-50 204
50-60 255
60-70 119
70-80 43
80-90 33
90-100 9

1. CA O’Flaherty, Transport Planning and Traffic Engineering, John
Wiley & Sons, Inc., New York; Toronto, 2002.
2. McShane & Roess, Traffic Engineering, Prentice‐Hall of India Pri
vate Ltd, New Delhi‐ 110001, 1990.
3. Kadiyali & Lal, Principles and Practices of Highway Engineering,
Khanna Publishers, Delhi‐ 6, 1996.
4. Chakarborty & Das, Principles of Transportation Engineering, Pre
ntice‐Hall of India Private Ltd, New Delhi‐110001.
5. L. R. Kadiyali, Traffic Engineering and Transport Planning, Khan
na Publishers, 2‐B, Nai Sarak, Delhi‐ 110006, 1999.
53

2.2_Traffic Studies_Speed Studies_045446.pptx

Related slideshows

More Related Content

Similar to 2.2_Traffic Studies_Speed Studies_045446.pptx

Similar to 2.2_Traffic Studies_Speed Studies_045446.pptx (20)

Recently uploaded

Recently uploaded (20)

2.2_Traffic Studies_Speed Studies_045446.pptx

Editor's Notes