Spot Speed Study

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Spot Speed Study Powered By Docstoc
					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 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
   Answer questions in manual
   Prepare your presentation