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