Spot Speed Study - University of Tennessee at Martin
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Transcript Spot Speed Study - University of Tennessee at Martin
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 Statistics
Average
speed
Speed data
Grouped
Not grouped
u = uj/N
Standard
deviation
Speed data
Grouped
s=
f(ui – u)2
N-1
Variance
s2
Not grouped
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
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
85%
50%
Frequency histogram example
Northbound Frequency Histogram
35
Frequency (f i)
30
Modal Speed = 31 mph
Modal Speed = 33 mph
25
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
Frequency (%)
10.00
8.00
6.00
4.00
Pace
28-34 mph
2.00
0.00
10
15
20
25
30
Speed (mph)
35
40
45
50
Cumulative frequency
distribution curve
Cumulative Frequency Curve
110.00
100.00
90.00
P85 = 35.5 mph
Frequency (%)
80.00
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
Speed Class (mph)
40
50
60
Helping calculation table
Interpret and conclude
Answer questions in manual
Prepare your presentation