Post Number: 27
|Posted on Friday, September 03, 2010 - 03:05 pm: |
The speed limits are based on the result of speed studies. Speed studies are typically conducted using a radar gun to measure the speed of 120 vehicles over a two hour period during non peak hours at several different locations along a roadway. Once the studies are complete they are evaluated to determine the 85th percentile speed. This is the speed that 85 percent of the drivers travel at or lower while the remaining 15 percent travel above that speed. For example, if the 85th percentile speed was 47mph, then 85 percent were travelling 47mph or less while 15 percent were travelling faster than 47mph. Using the 85th percentile speed, the limit is then set to the nearest 5mph.
While a roadway may appear to look similar throughout its length, the measurements may not. The speed limits reflect how the speed measurements were different in different areas.
Assistant Director of Engineering