Speed limits set based on road type, traffic flow

Hot Springs County Road and Bridge Supervisor Shane Rankin provided information on how speed limits are determined on county roads and elsewhere. 

Rankin said, “Mainly the county doesn’t set the speed limits. The speed limits are an engineered study. Basically, in layman’s terms, setting a speed limit must be established by a WYDOT study. When the speed limit is posted, it should be within five miles per hour of the 85% of free-flowing traffic.”

WYDOT puts counters across the roads, which are small rubber air hoses that are stretched over the road surface. This measures how many cars and semi-trucks are driving on the road and what their speed is. These hoses are left out for seven days, most of the time. WYDOT also figures in how many driveways are accessing the road and its approaches. All the data is collected and they statistically examine it and see where the 85% is at, meaning what speed 85% of the traffic is flowing. There are some vehicles going very fast and others very slow, but the statistical measurement they focus on it is the 85% majority. Based on this result, they will set the speed limit. 

Rankin said, “There can be roads that cross the highway that can be directly across from each other, such as West and East Sunnyside Road, where the speed limit is 45 miles per hour and the other is 35 miles per hour, but the statistical measurements are different. These are totally different roads. West Sunnyside is really long and mostly straight with a couple of curves. However, on East Sunnyside, there is a straightaway, but there are cattle guards, railroad tracks, sharp windy curves and narrow pathways. These elements made it a slower speed limit road.” 

Classified ads that ran previously the Independent Record questioned why there was a difference in the speed limit on East and West Sunnyside.

Rankin added, “In no circumstance should a speed limit be posted below the lower limit of the 10 miles per hour pace speed. So whatever that 85% is, they cannot post 10 miles per hour below that. If the engineered study comes out and it says there 85% of people are running at 50 miles per hour, you cannot post it below 40 miles per hour.”

Rankin also said, “All of the speed spot data and information described shall be collected by engineers or technicians who have been properly trained by the WYT2/LTAP Center field data who are through the University of Wyoming Engineering Program. The data analysis required to make the final recommendations on setting proper speed limits can be conducted by professional engineers only. We don’t go out and just throw up a speed limit sign, we have to go through an engineered study in order to do a speed limit.”