Bethel Maine
E & W Truck Speed 2001
The JOHO image illustrates a
different arrangement of date from the other traffic images at this web site.
Using the same WIM sensor data files as the other WIM images of the Bethel Type
10 traffic, we made this image showing truck speeds. The image is an example of
the result of a simple change in the directives telling JOHO which fields
to read in the data file. Here you can quickly discern patterns in the truck
speeds at the WIM site.
Please see the description of the Kittery
November image for a more detailed description of JOHO image
concepts. Remember that traffic count image has a different layout!
This image shows the total number of trucks (FHWA
Types 4-14) at each speed passing the WIM sensor in Bethel, Maine for all 2001.
The image contains 2,304 data points. This is far more information than
traditional graphics programs can display.
Image Layout
The image has twelve panels, each showing one
month in 2001, starting in the upper left and ending in the lower right. Each
column of a panel represents one hour in the day, starting with the hour from
midnight to 1 AM in the left column (as labeled in the December panel). The
right column of cells represents the hour from 11 PM to midnight. Each column
counts all the trucks in the month that passed the sensor at that hour, no
matter what day of the month they passed. The speed of the trucks is measured
vertically, from 30 mph at the bottom to 100 mph at the top.
Each colored cell indicates the total number of
trucks passing the sensor, in either direction, at that speed, during that hour,
sometime during the month. The legend at the right indicates the relation
between color and number of trucks. The image indicates counts of fewer than 200
as the dark blue color at the bottom of the legend. At about 550 trucks the
color changes from green to orange. The white at the top of the legend indicates
a count of 1,200 trucks or higher.
Image Interpretation
The most
obvious feature is that the third row from the bottom (46-55 mph) has the most
trucks. This is good news because the speed limit at the WIM site is 50 mph.
Most of the trucks pass during working hours. In July, August, and October there
is a peak in the count around noon. There
are more trucks in October (1,100 or more per hour) than any other month.
The hourly Type 10 E image for this site shows
a significant decrease in Type 10 truck traffic during September, perhaps
because of the 9/11 attacks. The decrease is also evident here. April and
December have the fewest trucks.
The fourth
row from the bottom (56-65 mph) shows many speeding trucks. Close inspection of
the different months shows that January, August, and October have the most
speeding trucks.
This type of
image could help enforcement agencies target the location at times when they
will have the most success. By combining this image with hourly traffic count
images enforcement can be scheduled at times when speeding is particularly
dangerous because of crowded roads.
You can see a
different view of the same information if you inspect the image
of the percentage of trucks that are going a given speed.
