# Spot Speed Study by cmk16156

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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
Data Collection
   Name of the safety officer
   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 Statistics
Average     Speed data
speed       Grouped             Not grouped
u = uj/N

Standard    Speed data
deviation   Grouped             Not grouped

s=   f(ui – u)2
N-1

Variance    s2
Types of Speed Measurements
Median 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   The spot speed below which i percent of the
speed            vehicles travel, e.g. 85th-percentile speed

Pace             The range of speed that has the greatest number
of observations; usually 10-mph range

85%
50%
Frequency histogram example
Northbound Frequency Histogram

35

30
Modal Speed = 31 mph                        Modal Speed = 33 mph
25
Frequency (f i)

20

15

10

5

0
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)
Frequency distribution curve
Frequency Distribution

12.00

10.00
Frequency (%)

8.00

6.00

4.00
Pace
28-34 mph
2.00

0.00
10   15    20    25       30          35   40   45   50
Speed (mph)
Cumulative frequency
distribution curve
Cumulative Frequency Curve

110.00
100.00
90.00
P85 = 35.5 mph
80.00
Frequency (%)

70.00
60.00
50.00
Median Speed=P 50= 31 mph
40.00
30.00
20.00
10.00
0.00
0   10             20           30          40           50   60

Speed Class (mph)
Helping calculation table
Interpret and conclude