Can highway underpasses help migrating deer cross safely and reduce vehicle collisions?

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Wildlife–vehicle collisions are a major safety concern for motorists and can be a significant source of wildlife mortality. Roads can also impede animal movements and reduce habitat connectivity. For migratory ungulates, these problems can become worse where roads cut across migration routes. In Southwest Wyoming, USA, a 21-km section of U.S. Highway 30 overlaps a critical winter range and migration route used by thousands of mule deer (Odocoileus hemionus).

To reduce deer–vehicle collisions (DVCs) and maintain migratory connectivity, the Wyoming Department of Transportation installed seven concrete box-culvert underpasses, with continuous wildlife-proof fencing between the crossing structures. Researchers evaluated this mitigation project using a before-and-after comparison of DVC rates and remote-camera monitoring to count mule deer using the underpasses and estimate passage rates over time.

The three years of monitoring covered three migration cycles: autumn migrations in 2008, 2009, and 2010; winter use; and spring migrations in 2009, 2010, and 2011. Researchers documented 49,146 mule deer moving through the underpasses. Among deer approaching the underpasses, passage rates steadily increased from 54% in Year 1 to 92% in Year 3. Peak autumn migration movements occurred in mid-December, while peak spring movements occurred in mid-March and early May.

Underpass and fence installation reduced DVCs by 81%. The authors state that DVCs could have been eliminated altogether had fence gates remained closed and cattle guards remained clear of snow. The findings suggest that underpasses combined with wildlife-proof fencing can improve highway safety for motorists while providing safe, effective movement corridors for large populations of migratory mule deer.

© 2012 The Wildlife Society.