U4 Spot Speed Study

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TRAFFIC AND HIGHWAY ENGINEERING LAB

U4 - SPOT SPEED STUDYSECTION 10 / GROUP 10

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1.0 INTRODUCTION

Speed is the rate of movement of a vehicle, generally expressed in kilometers per hour. A spot

speed study is a study of traffic speed at one point or spot on a traffic way. It consists of a series or a

sample of observations of the individual speeds at which vehicles are approaching an intersection orpassing a point at a non-intersection location. These observations are used to estimate the speed

distribution of the entire traffic stream at that location, under the conditions prevailing at the time of the

study.

Spot speed studies can be used to study speeds at problem locations in order to determine

whether speeds are too high and if complaints received are justified, for accident analysis in order to

determine the relationship of speed to accidents which may help in developing corrective measures, and

for before-and-after studies in order to evaluate the effect of some change in controls or conditions.

In relation with this study, there has been several complaints of vehicles speeding along the Jalan

Kluang. This poses a danger to motorists, pedestrians and cyclists as there is a lot of activity in the area.

Furthermore, there is plenty of right-turning movements along this stretch of road, with no storage lanes

provided for right-turners. This is dangerous because the right-turners stop on the fast lane and have no

protection.

2.0 OBJECTIVE

The objectives of this study are:

2.1 To determine the speed characteristics of traffic at the location.

2.2 To justify the problem of speeding at the location.

3.0 APPARATUS

3.1 Radar Gun

3.2 Forms SS1 and SS2 (Refer to Appendix)

3.3 Graph Paper (3 nos)

3.4 Safety Vest





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4.0 PROCEDURE

4.1 The road in front Taman Universiti was chosen for our spot speed study.

The spot at which the speed data will be collected is identified.

4.2 The radar gun is used to measure the speed of vehicles according to their respective vehicle

class – Class 1 (Motorcycles), Class 2 (Cars), Class 3 (Vans & Medium Trucks), and Class 4

(Large Trucks & Buses).

[The operator of the radar gun is made sure not seen by the motorists]

4.3 All speed measurements recorded in Form SS1.

4.4 Based on Form SS1, the mean, maximum and minimum speed of vehicles is determined

according to their class. The findings are commented.

4.5 The data is transferred in Form SS1 to Form SS2.





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4.6 The following are plotted:

(a) Frequency Histogram (Percentage of vehicles vs. Speed )

(b) Frequency Distribution Curve (Percentage of vehicles vs. Speed )

(c) Cumulative Frequency Distribution Curve (Cumulative percentage vs. Speed )

4.7 The following speed characteristics is determined:

(a) Mean speed

(b) Median speed

(c) Mode speed

(d) 85-th Percentile speed

(e) Standard deviation

(f) Pace





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5.0 RESULTS & DATA ANALYSIS

Form SS1

Location: Road in front Taman Universiti

Date: 04 April 2013 Time: 8:45 - 9:45 am Weather: Windy

Time

Sport Speed (km/h)

Vehicle Class

1 2 3 4

8:45-

9:00 am

32 39 35 60 45 62 33 40 35 35 37 30

50 51 46 65 66 40 42 29 28 32 33 39

63 62 22

38 42 50

9:00-

9:15 am

34 32 40 25 32 21 50 27 43 36 32 35

25 35 41 60 65 62 45 46 47 43 30 32

38 63 42 51 35

23 40 25

9:15-

9:30 am

33 32 29 52 60 21 35 38 41 37 30 35

30 35 37 25 36 54 40 39 29 31 36

37 38 42 31 67 39 32 33

55 23 43

9:30-

9.45 am

40 42 31 23 62 34 27 41 39 32 36 28

35 36 37 37 53 26 32 43 29 33 30 37

63 50 42 43 31 42

32 25 60 33 32 44

58





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Form SS2

Speed

Class

(km/h)

Class

Mid

value, x

(km/h)

Class

Frequency, f

Cumulative

Frequencyf x

Percentage in

Class

Cumulative

Percentage

15-19 17 0 0 0 0.00 0.00

20-24 22 6 6 132 4.51 4.51

25-29 27 14 20 378 10.53 15.04

30-34 32 29 49 928 21.80 36.84

35-39 37 31 80 1147 23.31 60.15

40-44 42 22 102 924 16.54 76.69

45-49 47 5 107 235 3.76 80.45

50-54 52 9 116 468 6.77 87.22

55-59 57 2 118 114 1.50 88.72

60-64 62 11 129 682 8.27 96.99

65-69 67 4 133 268 3.01 100.00

∑f=133∑ f x

=5276

∑Percentage

=100.00





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6.0 CALCULATION

1. From SS1,

Speed

Class

(km/h)

Class

Midvalue,

x (km/h)

Class Frequency, f f x

Vehicle Class Vehicle Class

1 2 3 4 1 2 3 4

f 1 f 2 f 3 f 4 f 1 x f 2 x f 3 x f 4 x

15-19 17 0 0 0 0 0 0 0 0

20-24 22 0 6 0 0 0 132 0 0

25-29 27 2 5 5 2 54 135 135 54

30-34 32 7 4 2 16 224 128 64 512

35-39 37 11 3 5 12 407 111 185 444

40-44 42 4 7 7 4 168 294 294 168

45-49 47 1 1 3 0 47 47 141 0

50-54 52 2 6 1 0 104 312 52 0

55-59 57 0 2 0 0 0 114 0 0

60-64 62 0 11 0 0 0 682 0 0

65-69 67 0 4 0 0 0 268 0 0

∑= 27 49 23 34 1004 2223 871 1178

Mean speed =

where

f = frequency of observations in the particular class

x = mid-point of each class

n = total number of observations = ∑f

Vehicle Class 1 (Motorcycles)

Mean speed =

= 1004 / 27 = 37.19 km/h

Maximum speed = 51 km/h

Minimum speed = 25 km/h





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Vehicle Class 2 (Cars)

Mean speed =

= 2223 / 49 = 45.37 km/h



Vehicle Class 3 (Vans & Medium Trucks)

Mean speed =

= 871 / 23 = 37.87 km/h



Vehicle Class 4 (Heavy Trucks & Buses)

Mean speed =

= 1178 / 34 = 34.65 km/h



Comment:

From the data collected, we have calculated the mean speed, as well as identified the maximum speed

and the minimum speed for each class of vehicles. The mean speed for class 1 (Motorcycle) is 37.19

km/h, class 2 (Cars) is 45.37 km/h, class 3 (Vans & Medium Trucks) is 37.87 km/h and class 4 (Heavy

Trucks and Buses) is 34.65 km/h.

Cars have the highest mean speed is which is 45.37 km/hr. Due to the speed limit of the road was 60

km/hr , this caused many car drivers driving below the speed limit. The mean of all the classes of vehicles

is average because there are traffic light nearby and university at beside of the road. Driver will need time

to speed up and have to lower down the speed when near university area.

However, of all the class of vehicles, we identified the highest of maximum speed of 67km/h, which is

already over the speed limit of the road of 60km/h. This was dangerous for all either motorist, pedestrians

and cyclist.

Therefore, body protection and storage lane provides are needed in reducing and preventing road

accident to occur.





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2. From SS2,

(a) Median Speed

The median can be determined from the cumulative frequency distribution curve.

From the cumulative frequency distribution curve, the median speed is 37.5 km/h.

There are 133 vehicles in total. So the median will be the 67th vehicle.

According to cumulative frequency of form SS2, the 67th vehicle was fall in the speed class 35 -

39 km/h.

By using the formula,

Median speed =

where

L=lower limit of the class in which the median class lies.

n= total number of observations

=cumulative number of observation up to the lower limit of the class in which the median lies

=number of observations in the class in which the median lies.

C=speed interval of the group.

Median speed =

=

= 37.32 km/h





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(b) Mean Speed

By using the formula,

Mean speed =

where

f = frequency of observations

x = mid-point of each class

n = total number of observations = ∑f

Mean speed =

= 5276 / 133

= 39.67 km/h

(c) Mode Speed

From the Frequency Histogram (Graph 1), the model class is 35-39 km/h. To determine the

mode speed from the Frequency Histogram, by looking at the highest bar and joining its top left

corner to the top left of the next bar, and the top right corner to the top right corner of the previous

bar, where they intersect is the mode.

Therefore, the mode speed from the grouped data are 35.5 km/h.

The mode speed also can be calculated by using the following formula:

Li is the lower limit of the modal class.

f i is the absolute frequency of the modal class.

f i-1 is the absolute frequency immediately below the modal class.

f i+1 is the absolute frequency immediately after the modal class.

ai is the width of the class containing the modal class.

= 35.4 km/h

http://www.vitutor.com/statistics/descriptive/frequency_distribution.html#cl



http://www.vitutor.com/statistics/descriptive/frequency_distribution.html#af



http://www.vitutor.com/statistics/descriptive/frequency_distribution.html#we










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(d) 85th

Percentile Speed

The speed at or below which 85 percent of the motorists drive on a given road unaffected by slower traffic

or poor weather.

P85 = 52.0 km/h

(e) Standard Deviation

The description of central tendency is not sufficient to define a distribution, therefore a measure of

dispersion or spread is required.

Standard Deviation =

where

f = frequency of observations

x = mid point of each class

n = total number of observation = ∑f

Speed Class

(km/h)

Class Mid

value, x (km/h)Class Frequency, f f x f x

2

15-19 17 0 0 0

20-24 22 6 132 2904

25-29 27 14 378 10206

30-34 32 29 928 29696

35-39 37 31 1147 42439

40-44 42 22 924 38808

45-49 47 5 235 11045

50-54 52 9 468 24336

55-59 57 2 114 6498

60-64 62 11 682 42284

65-69 67 4 268 17956

∑f=133 ∑ f x =5276 ∑ f x2 =226172





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=

= 11.31 km/hr

Alternative method to estimate the standard deviation:

Estimated standard deviation =

where

P85 = 85th Percentile Speed and

P15 = 15th Percentile Speed

From the Cumulative Frequency Distribution Curve (Graph 3),

P85 = 52.0 km/h

P15 = 29.5 km/h


= 11.25 km/h

(f) Pace

Pace is the 10 km/h range in speed in which the highest number of observation was recorded.

From the Frequency Distribution Curve (Graph 2), the pace is 32 - 42 km/h and approximately 45% of the

vehicles are in pace.

Comment:

According to the calculation, our median speed is about 37.5 km/h, the mean is 39.67 km/h and the mode

is 35.5 km/h. The standard deviation is about 11.30 km/h. From the graph of cumulative frequency

distribution curve , we found out that the 85 th percentile speed is 52.0 km/h. This speed indicates the

speed that most motorist on the road consider safe and reasonable under ideal conditions. And from the

graph of frequency distribution curve, the pace is 32 - 42 km/h and approximately 45% of the vehicles

are in pace.

From the result, we are known that the heavy cars were the main vehicles which contribute an accident.

So, we must take action to avoid accident. Here are suggestion and recommendations of road:





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i. The signboards like on speed limit, overtaking and sharp bends at locations prone to accidents

must be placed to caution motorist.

ii. The cat eye should be placed to on the road to decrease the speed of vehicles on this road.

7.0 DISCUSSION

From this spot speed study, we are known for traffic operation establishing speed limits,

determining safe speed at approaches to intersections. The road along Batu Pahat - Kluang highway was

not safe and actions must be taken to avoid any road accidents.

From the finding, the mean speed, maximum speed and minimum speed of each class is

determined by using form SS2. This two lane highway have a speed limit of 60km/h. Each of the mean

speed of class vehicles gives the different speed. For the class 1 is 37.19 km/h, class 2 is 45.37 km/h,

class 3 is 37.87 km/h and class 4 is 34.65 km/h. The highest mean speed is class 2 and the lowest mean

speed is class 4.

Based on the mean speed for class 2 that we found, it seems the speed is under the speed limit.

This are cause by a few factor that can be influence such as, the lane is straight and there are junctions

nearby, so there do not have any speed up. However, a few number of cars still exceeded the speed limit.

Due to this, some drivers of other class vehicles was alert by driving carefully then slow down their vehicle

speed.

Base on analysis, the standard deviation of this road according our observation is 11.30 km/hr,

and the pace is between 32 km/h to 42 km/h. The 85th percentile speed as obtained from the cumulative

frequency distribution curve shown is 52.0 km/h. It is important to have a good guideline for the

appropriate speed limit for that road and it indicates that the speed most of the motorists on the road to

considered safe and reasonable under ideal condition.





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8.0 CONCLUSION

The objectives of this survey are to determine the speed characteristics of traffic at the location

and to justify the problem of speeding at the location. From this experiment, we can be concluded that

section of this road cannot be considered as 100% safe at this location even though the results of the

finding which show that mean, median, pace and 85th percentile speeds have all are under the 60 km/hr

speed limit, however, there were some vehicles which over the speed limit. Therefore, actions should be

taken by the government as well as the society to reduce the number of road accidents.

9.0 REFERENCES

... BFC 3082. Traffic Engineering And Safety, Second edition, Department of Geotechnical &

Transportation Engineering, Faculty Of Civil & Environmental Engineering UTHM.

... Paul H. Wright & Radnor J. Paquette; Highway Engineering (5th

Edition), Georgia Institute of

Technology, 1979.

... Nicholas J. Garber; Lester A. Hoel; Traffic & Highway Engineering (3rd

Edition), University of Virginia,

1995.

... Bent Tagesen; Highway Engineering & Traffic (1st Edition), Technical University of Denmark.

... http://www.vitutor.com/statistics/descriptive/mode.html

10.0 APPENDIX

... Form SS1 and SS2

... Graph 1: Frequency Histogram (Percentage of vehicles vs. Speed )

... Graph 2: Frequency Distribution Curve (Percentage of vehicles vs. Speed )

... Graph 3: Cumulative Frequency Distribution Curve (Cumulative percentage vs. Speed )

http://www.vitutor.com/statistics/descriptive/mode.html



U4 Spot Speed Study

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