spot speed study. before anything else read the manual carefully. it is your homework what is...
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Spot Speed Study
Before anything else
Read the manual carefully. It is your homework
What is covered in the following slides is just general
General
The data is to be used for assessing general speed trends and for setting speed limits.
The equipment for our data collection procedure is a hand-held radar. Radar usage Radar checkout
Data Collection
Name of the safety officer Choose section of road Not close to intersection Off-peak period during daylight
hours on a typical weekday Hide I will contact Police to cover you
Data collection form
Data analysis
What should you do with the collected speeds? What else, statistical analysis!
Remember that old stuff: Mean, standard deviation,… Plus a few more things
Speed StatisticsAverage speed
Speed data Grouped Not grouped
Standard deviation
Speed data Grouped Not grouped
Variance s2
u = uj/N
s = f(ui – u)2
N - 1
Types of Speed MeasurementsMedian speed
The speed at the middle value in a series of spot speeds. Or, 50th-percentile speed
Modal speed The speed value that occurs most frequently in a sample of speeds
ith-percentile speed
The spot speed below which i percent of the vehicles travel, e.g. 85th-percentile speed
Pace The range of speed that has the greatest number of observations; usually 10-mph range
50%
85%
Frequency histogram example
Northbound Frequency Histogram
0
5
10
15
20
25
30
35
22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Speed Class (mph)
Fre
qu
en
cy
(f i
)
Modal Speed = 31 mph Modal Speed = 33 mph
Frequency distribution curve
Frequency Distribution
0.00
2.00
4.00
6.00
8.00
10.00
12.00
10 15 20 25 30 35 40 45 50
Speed (mph)
Fre
qu
en
cy
(%
)
Pace 28-34 mph
Cumulative frequency distribution curve
Cumulative Frequency Curve
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0 10 20 30 40 50 60
Speed Class (mph)
Fre
qu
en
cy
(%
)
P85 = 35.5 mph
Median Speed=P50= 31 mph
Helping calculation table
Interpret and conclude
Answer questions in manual Prepare your presentation