The Role Of Trees In Deer-Vehicle Accidents

Each year, collisions between cars and animals result in injuries to thousands of people, the death of millions of animals, and economic losses in the billions of dollars. Though many of these accidents are just that—accidents—research suggests that some of them, especially those involving reptiles like snakes, are intentional. Whether intentional or not, however, the scale of the problem is huge.

This article analyzes GPS data on 998 animal-vehicle collisions involving roe deer between October 2014 and October 2016 in Göttingen, Germany. The analysis involved looking at the levels of “trees outside forests” (TOF) where the accidents took place. TOF includes hedges, bushes, isolated trees, and other such vegetation outside the range of a forest.

The researchers found that the spatial distribution of accidents followed a significantly clustered pattern in which certain areas were “hotspots” for animal-vehicle collisions. Areas of medium risk for accidents had a significantly greater presence of TOF compared to neighboring sections of roads. Areas of high risk showed high TOF presence as well, though the difference in TOF levels between areas of high risk and nearby reference road sections was not significant. Nevertheless, the highest TOF coverage occurred closest to major accident hotspots.

The researchers hypothesized that the lack of significant differences between TOF in areas of highest risk and their neighboring reference areas may be attributed to the small sample sizes of high-risk areas (again, because accidents were clustered around a few especially high-risk hotspots). Additionally, although TOF were absent from several individual hotspots, a visual assessment showed that there were still forest edges in those areas. Overall, the data supports the conclusion that vegetation alongside roads, whether in the form of TOF or forest edges, increases the likelihood of animal-vehicle collisions.

The researchers conclude that TOF may attract deer because these areas provide sources of food and cover from predators. Additionally, TOF may reduce visibility for drivers and deer alike, which could increase the risk of collision. The researchers point out that past studies demonstrate how reducing roadside vegetation can decrease the number of animal-vehicle collisions. Therefore, the researchers suggest that TOF management near roadsides should be considered one component of a larger strategy to reduce animal-vehicle collisions. Advocates can use this information to pressure policy makers into legislating TOF management. Though simple, it offers a promising approach to promoting the interests of humans, animals, and the economy alike.