Cost-effective approach to reducing collisions with elk by fencing between existing highway structures

Collisions with large ungulates cause serious human and animal injuries and significant property damage. Therefore, wildlife crossing structures are increasingly included in new road construction to reduce wildlife–vehicle collisions, while still allowing wildlife to safely cross roads. Recently, state and federal transportation budgets have declined, concomitantly reducing the construction of wildlife crossing structures, which are generally tied to large-scale reconstruction projects that are delayed for decades into the future. Nevertheless, even during times of fiscal constraint or temporal delay, it is still necessary to reduce collisions with wildlife and maintain habitat connectivity. Therefore, it is important to find cost-effective and functional alternatives. Retrofitting roadways with wildlife exclusion fencing that directs animals to existing highway structures (e.g., sufficiently sized bridges and culverts) is a possible costeffective, interim solution that needs further testing. Along Interstate-17 in northern Arizona, we heightened 9.17 km of right-of-way barbed wire fence to 2.4 m to guide elk (Cervus canadensis) to 2 large bridges and 2 modified transportation interchanges. We evaluated occurrence of elk–vehicle collisions, elk use of existing structures, and GPS movements of elk preand post-fencing retrofit. Post retrofit, there was a 97% reduction in elk–vehicle collisions for the 9.17 km stretch of road. There were also no increases in collisions at the fence termini (area within 1.61 km from fence ends) nor in the remaining sections, indicating that elk were not simply forced to those areas. We documented a 217% and 54% increase in elk use of the 2 large bridges, but no elk use of the transportation interchanges. GPS relocation data from 31 elk showed a statistically insignificant decrease, from 0.07 to 0.03 crossings per approach preand post-fence modification, respectively. Elk road crossings, determined through GPS relocations, were concentrated around the bridge structures rather than being evenly distributed across the treatment sections, and similar to collisions, crossings did not increase on adjacent fence termini. Using the Huijser et al. (2009) estimate of $17,483 for the cost to society of an elk–vehicle collision, the level of collision reduction on this stretch of road will recoup project costs in <5 years. Our results indicate that, under certain circumstances, retrofits can in the short-term reduce wildlife–vehicle collisions on roadways that are not scheduled to be reconstructed in the near future. However, for the long-term, areas with significant wildlife– vehicle collisions or habitat fragmentation should have appropriately designed, located, and maintained wildlife crossings with exclusionary funnel fencing.