Median Treatment May Impact Wildlife-Vehicle Collisions on California Highways

The Wildlife Society Conference 2025
Authors
Ben Hodgson, Road Ecology Center, UC Davis
Lorna Haworth, Road Ecology Center, UC Davis
Leo Hecht, Road Ecology Center, UC Davis
Ash Henderson, Road Ecology Center, UC Davis
Laura Morris, Road Ecology Center, UC Davis
Shannon Lemieux, Road Ecology Center, UC Davis
Michelle See, Road Ecology Center, UC Davis
Fraser Shilling, Road Ecology Center, UC Davis
Abstract

Transportation infrastructure can restrict wildlife movement and increase wildlife-vehicle collisions (WVCs) that kill over 48,000 deer in California annually. Medians, which separate opposing traffic lanes, vary in type (e.g., concrete barriers, metal guardrails, vegetated strips) and may influence WVC rates. At Caltrans' request, we assessed the impact of median types on WVC rates along California highways. Using Google Street View, we categorized median types at 1,069 mule deer (Odocoileus hemionus) WVC sites in Caltrans District 9 and 332 western gray squirrel (Sciurus griseus) WVC sites in Caltrans District 2 between January 2015 and April 2024. Chi-square tests showed significant differences between WVC site medians and randomly generated site medians, suggesting that median type affects WVC density for both species. Additionally, we analyzed 73 paired highway transects where the median transitions from one type to another, comparing WVC rates along 1-mile stretches. Wilcoxon tests revealed WVC rates were 1.95 times higher along metal guardrails than vegetated strips (p=0.045), though other pair comparisons were not significant. These findings highlight the influence of median treatments on WVCs and suggest that transportation planning should consider wildlife connectivity impacts to reduce collisions.