Wyoming roadway.
Elk crossing Wyoming roadway. © Mark Gocke


Not So Fast: Lowered Speed Limits Aren’t Stopping Wildlife-Vehicle Collisions

A new study shows drivers aren’t obeying the speed limits meant to reduce accidents.

Lander, WY

Wildlife-vehicle collisions are a major hazard for drivers and wildlife alike. Every year, more than 2 million of these crashes occur in the United States, leading to human injuries, costly vehicle repairs, and loss of wildlife. It’s commonly believed that reducing speed limits can stop the carnage. Not so, says a new study led by The Nature Conservancy in Wyoming (TNC).

This study, led by TNC scientist Corinna Riginos, tested the idea that reducing night-time speed limits during high-risk times will cause motorists to drive more slowly, giving them more time to avoid hitting animals on the road. The problem is, the average driver didn’t obey the lower posted speed limit, and there was no change in the number of wildlife-vehicle collisions. 

Prior to this study, almost no data existed on whether reducing speed limits could reduce wildlife-vehicle collisions. To test the practice, the researchers partnered with the Wyoming Department of Transportation to change the speed limit at six sites in Wyoming known to be important winter and migration areas for mule deer. The speed limit was reduced from 70 to 55 miles per hour at night since most wildlife-vehicle collisions occur in the dark. The researchers then compared the number of collisions at the test sites before and after the speed limit change. They also tested for differences in vehicle speed in the reduced speed limit zones and in adjacent locations where the speed limit was not reduced. On average, drivers slowed down by only 3-5 mph rather than the required 15 mph, and there was no evidence that the reduced speed limit led to fewer wildlife collisions.

“The only sure way to significantly reduce these accidents is to build over- or underpasses that allow animals to cross roads without touching the pavement,” says Riginos. “Changing human behavior is tough.”

“Most of us would like there to be simple and inexpensive solutions for complex problems,” says Marcel Huijser, a co-author and scientist with the Western Transportation Institute at Montana State University.  “But this does not necessarily mean such solutions exist. Wildlife fences in combination with under- and overpasses are costly, but they do address the problem, and because they reduce costly collisions, they can also pay for themselves.”

Although the price for crossing infrastructure is high, so is the cost of no action. In Wyoming, wildlife-vehicle collisions cost more than $50 million in human injury, property damage and wildlife loss every year. About 85% of wildlife-vehicle collisions in the state involve mule deer, and at an average cost of $10,500 per accident (twice that if you hit an elk) the cost of this problem adds up quickly.

This year, the state of Wyoming and the Federal government committed funds toward building crossing structures.

  • Wyoming Game and Fish Commission:  $2.5 million
  • Wyoming Department of Transportation: $1 million
  • U.S. Department of Transportation Better Utilizing Investments to Leverage Development (BUILD grant:  $14.5 million)

The study was sponsored by the Wyoming Department of Transportation.

Read the full study.

The Nature Conservancy is a global conservation organization dedicated to conserving the lands and waters on which all life depends. Guided by science, we create innovative, on-the-ground solutions to our world's toughest challenges so that nature and people can thrive together. We are tackling climate change, conserving lands, waters and oceans at an unprecedented scale, providing food and water sustainably and helping make cities more sustainable. Working in 75 countries and territories: 37 by direct conservation impact and 38 through partners, we use a collaborative approach that engages local communities, governments, the private sector, and other partners. To learn more, visit www.nature.org or follow @nature_press on Twitter.