Car-on-animal crashes cost Californians millions. New research lists roadkill ‘hot spots’

You might see it every day on your morning commute, and you probably avoid looking at it as much as possible.

But off-putting as it might sound, drivers voluntarily uploading photos of roadkill has helped UC Davis researchers collect important data related to highway safety and wildlife impact.

The UC Davis Road Ecology Center has used that data, from the California Roadkill Observation System, and more to map out California’s roadkill “hot spots.”

The City of Trees is among them.

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High-density wildlife vehicle collision hotspots for 2015 to 2018. Hotspots can vary in length from 1 to several miles. Density is expressed as number of incidents per mile per year. UC Davis Road Ecology Center

An annual report released this week by university researchers details the economic costs of “wildlife-vehicle conflicts” on all of California’s highways and some local roadways, listing the Sacramento-Placerville area as one of several regions that sees animal carcasses turn up most frequently and with the greatest density per mile. Car-on-animal crashes happen frequently on Highways 49 and 50, as well as Interstate 80, the study says.

The UC Davis Road Ecology Center estimated the total direct cost of wildlife-vehicle conflicts in 2018 to be at least $232 million statewide, and perhaps as high as $500 million when factoring in unreported crashes.

Maps and data published by the university research center give additional insights into traffic incidents involving wildlife. The Road Ecology Center estimates 7,000 highway crashes involving deer and other “large wildlife” (cows, goats, mountain lions, etc.) happen every year in California.

Other hot spots include several Bay Area highways, and stretches of Highway 101 and Interstate 5 in both Southern California and the north part of the state. An interactive map can be found on the Road Ecology Center website and at

Mountain lions at risk

The study, released Wednesday, says that between 2015 and 2018, an average of 75 mountain lions a year were killed by traffic on California roadways, according to observations by volunteers, the California Highway Patrol, the Department of Fish and Wildlife and biologists.

Mountain lions reported killed on roads, or involved in traffic incidents by the California Roadkill Observation System, CDFW, CHP, or Winston Vickers and other biologists in Southern California. UC Davis Road Ecology Center

The animals are particularly vulnerable because as roaming predators, they cross roads and highways frequently.

“Mountain lions are important ecologically because they are the only large, widespread predator in most California ecosystems. ... A critical problem for mountain lions in California is that there is no formal program, system or requirement to report when they are killed on roads, which happens frequently.”

The mountain lion issue exemplifies “the need in California for a systematic and legislated approach to reporting wildlife mortality on roadways in order that we can understand the distribution, impacts and risk to wildlife populations and species,” the UC Davis report says.

“Wildlife populations may suffer significant losses from highways with high rates of WVC (wildlife-vehicle conflicts), which may cause ripple effects into surrounding ecosystems up and down the food chain,” the study says.

What can be done?

Projects to reduce wildlife vehicle collision can include wildlife crossings and better roadside barriers.

The study claims transportation agencies should be more proactive in their planning and implementations of these projects.

“Transportation agency planners and biologists are increasingly discussing wildlife-crossing structures and other projects as stand-alone safety and sustainability projects, providing a net benefit to drivers and wildlife, without the need for the projects to mitigate for further harm later.”

The ecologists also say it’s critical to prioritize known wildlife hot spots.

“There are hundreds of places on state highways and major roads where WVC is a priority,” the report says.

The annual report also says there should be ample funding for such projects due to Senate Bill 1 funding, which allocates $5.4 billion a year to California’s transportation infrastructure.

Researchers say state agencies should take advantage of the data they’ve collected, with the research center welcoming partnerships with Caltrans, Fish and Wildlife and other transportation and wildlife agencies across California.

The research effort was headed by Fraser Shilling, co-director of the Road Ecology Center. Shilling’s team has collected more than 60,000 observations of more than 430 species of roadkill between 2009 and July 2019 using the California Roadkill Observation System, which lets the public upload photos of roadkill directly to the center’s database.

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Michael McGough anchors The Sacramento Bee’s breaking news reporting team, covering public safety and other local stories. A Sacramento native and lifelong capital resident, he interned at The Bee while attending Sacramento State, where he earned a degree in journalism.