example of spot speed study - tun hussein onn...
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Example of Spot Speed Study
CHAPTER 1: Traffic Studies
A spot speed study was conducted along a state road experiencing frequent road accidents. The posted speed limit of the road is 60 km/h. The spot speed data collected are shown in the following table: Analyse the spot speed data & Present the findings of this study.
Solution:
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Mean speed = 9085/130
= 69.9 km/h
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Median speed L = lower limit of the class in which the median lies n = total number of observations f L = cumulative number of observation up to the lower limit of the class in which the median lies f m = number of observations in the class in which the median lies C = speed interval of the group
Solution:….cont’d
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Solution:….cont’d
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Pace Pace = the 10 km/h range in speed in which the highest number of observation was recorded
Solution:….cont’d
Therefore, the pace is 62 – 72 km/h and 30% of the vehicles are in pace.
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Solution:….cont’d
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85th Percentile Speed
The 85th percentile speed is the speed at or below which 85 percent of the motorists drive on a given road unaffected by slower traffic or poor weather.
This speed indicates the speed that most motorists on the road consider safe and reasonable under ideal conditions.
It is a good guideline for the appropriate speed limit for that road.
The 85th percentile speed as obtained from the cumulative frequency distribution curve shown below is 88 km/h.
Solution:….cont’d
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Standard Deviation
The description of central tendency is not sufficient to define a distribution, therefore a measure of dispersion or spread is required. Where f = frequency of observations in the particular class x = mid-point of each class n = total number of observations = Σf
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Solution:….cont’d
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Findings from this spot speed study: Mean speed = 69.9 km/h
Median speed = 68.1 km/h
Pace = 62 – 72 km/h
Percentage of vehicles in pace = 30%
85th percentile speed = 88.0 km/h
Driving over the speed limit = 95 / 130 = 73.1%
CHAPTER 1: Traffic Studies
Solution:….cont’d
Conclusion:
It can be concluded that speeding is a problem at this location and may have contributed to road accidents which have occurred at this location.
This is supported by the results of the findings which show that mean, median, pace and 85th percentile speeds have all exceeded the 60 km/h speed limit.
In addition, 30% of the drivers drive at speeds ranging between 62 – 72 km/h, and 85% of them drive at 88.0 km/h or below. 95 individual vehicles, or 73.1% of the vehicles, were detected to have driven over the speed limit.
CHAPTER 1: Traffic Studies
Suggest ways to control vehicle speeds at this location?
p/s: kahoot.it
Speed class
km/h
Frequency, f
40 – 44 0
45 – 49 5
50 – 54 13
55 – 59 27
60 – 64 50
65 – 69 66
70 – 74 72
75 – 79 52
80 – 84 24
85 – 89 15
90 – 94 5
A table show set of speed data collected on a rural highway in Malaysia during
a speed study. The posted speed limit of the road is 60 km/h.
a) Determine mean speed, median speed, pace, 85th-percentile speed and
standard deviation
b) As an engineer, give your justification based on your findings about the
speeding at this rural highway.
Class exercise: