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Effectiveness of Nighttime Speed Limit Reduction in Reducing Wildlife-Vehicle Collisions

Project #: 4w6435
Start Date: 12/05/2016
End Date: 12/31/2018
Status: Completed

As described in the final report, the research team conducted an experiment in which posted speed limits were reduced from 70 mph to 55 mph during dusk to dawn hours in key deer activity seasons at six sites in southwestern Wyoming. Drivers reduced their speeds in response to the posted speed limit reduction, but the average reduction was only 3-5 mph. At winter sites, where the reduced speed limit was in effect for seven months, there was no evidence of any reduction in wildlife-vehicle collisions (WVCs).  At migration sites, where the reduced speed limit was in effect for two months at a time, there was some evidence of fewer WVCs, although it was not clear that this could be attributed to the reduced speed limit.  The researchers recommended that a reduced posted speed limit is not an effective measure to reduce WVCs on high-speed rural two-lane highways.


The Wyoming Department of Transportation is interested in testing and developing a broad range of methods for reducing wildlife vehicle collisions.  One possible mitigation measure is to reduce posted speed limits in areas known to have high wildlife-vehicle collision rates, particularly at night when the majority of collisions occur. There is a need to understand whether such measures would be effective in reducing  WVCs, and whether they would be more effective under some circumstances than others.

Through this project, WTI will investigate the effects of  speed limit reductions at mule deer collision hotspots in Wyoming.  Researchers will study the effects of the speed limits on vehicle speeds, on the interactions between wildlife and vehicles, and on the number of observed collisions.


The objective of this project is to provide transportation planners with information about whether reducing nighttime speed limits is an effective means of reducing vehicle collisions with wildlife, which is a mitigation measure under consideration in some western states.


  • Marcel Huijser
    Marcel Huijser