Reduced speed limit is ineffective for mitigating the effects of roads on ungulates

Abstract

AbstractRoads obstruct wildlife movements, and wildlife‐vehicle collisions are a hazard to both animals and humans. Wildlife and transportation managers often consider reducing the speed limit to reduce wildlife‐vehicle collisions, but there is little empirical data to support or refute this measure. We experimentally reduced the nighttime speed limit from 70 to 55 mph on six stretches of highway that cross mule deer (Odocoileus hemionus) winter range or migration paths. Drivers consistently reduced their speeds, but only by 3–5 mi/h. Reduced speed limit did not make it any easier for deer to cross the road, indicating no benefit for habitat connectivity. At winter sites, the number of deer‐vehicle collisions was not affected by the reduced speed limit whereas at migration sites, collisions were modestly lower under the reduced speed limit. Given the small reduction in vehicle speeds, it is not surprising that there was little benefit of reduced speed limit for deer or people. We conclude that reduced nighttime speed limit is not an effective way to reduce wildlife‐vehicle collisions or make roads more permeable to wildlife due to poor compliance from motorists.