Wildlife-vehicle collisions (WVC) are an important, under-recognized impact on driver safety and anthropogenic mortality for species of wildlife that attempt to cross roads. The California Roadkill Observation System (https://wildlifecrossing.net/California) includes >255,000 WVC observations from state agencies, California Highway Patrol, and expert volunteers. Between 2015 and 2024, there were 1,009 state highway 1-mile segments with annual rates of collision with large wild mammals of at least 1/mile. To estimate the equivalent cost of reported collisions, crash coefficients were applied to different crash types. Fencing these highways would cost at least $200,000,000 to build and save $46,654,000/year, or >$900,000,000 for the 20-year lifetime of the fencing. The rate and cost of reported large mammal WVC has declined 10% per year for the last 10 years. The highest annual rate of large WVC reported was for US 101 in Marin County (4.6/mile). Outside of the Bay Area, the highest rate was for US 50 in W El Dorado County (3.7/mile). Several hotspot highways are targets for wildlife crossing planning, but little attention has been devoted to wildlife fencing, which is the measure that can reduce WVC.

Fraser Shilling is Director of the Road Ecology Center at UC Davis. He is also co-lead of the Transportation Ecology practice at Dudek. He organizes the International Conference on Ecology and Transportation. He also races outrigger canoes, gardens and loves his dog. Purple is his favorite color, chocolate is his preferred food group and he received his PhD from USC.