Study finds I-280 state’s deadliest road for mountain lions
About 70 mountain lions are fatally struck by vehicles on California’s 15,000 miles of highway each year — and the deadliest stretch of all for the protected species is Interstate 280 running through the Peninsula, according to a new study from UC Davis researchers.
Between 2015 and 2022, nearly one mountain lion died per mile of the eight-lane, 31-mile stretch of I-280 between San Bruno and Cupertino, according to the report, which also notes that the true number is likely underreported.
“I-280 has consistently been the deadliest from a human point of view, from a wildlife point of view, for collisions with wildlife in California,” said Fraser Shilling, director of the Road Ecology Center at UC Davis, which led the study. He said that a person gets killed hitting an animal on I-280 about every other year.
Winding through grassy hills dotted with shrubs and trees, the heavily traveled Bay Area freeway juts up against protected wilderness areas, Shilling noted, which makes it especially risky for wildlife crossings — and diamond-shaped yellow road signs along the freeway acknowledge this.
It’s one of the reasons why the highway has the highest rate and costs of collisions with all wildlife in the state for each of the past five years, according to the report, which relied on data and reports from UC Davis as well as hundreds of CHP officers, California Department of Transportation maintenance staff and state and federal Fish and Wildlife agency staff.
Those collisions cause myriad problems, and not just for the animals, the report noted. Besides injuries and fatalities for both the animals and the people who accidentally hit them, each collision comes with a significant cost — on the 31 miles of I-280 alone, the estimated annual cost of wildlife vehicle collisions is $5.8 million, a figure that includes things like
hospital bills, property damage to cars or the highway and the cost of an emergency response and the labor that comes with it.
For all of California, such collisions account for $200 million to $400 million in costs per year, based on crash cost data reported to the Federal Highway Administration.
“And this is just from a financial point of view, let alone the emotional harm from people getting injured or dying on a highway,” Shilling said. “It’s a predictable, preventable incident.”
For a species like mountain lions, the collisions create yet another threat to their existence, he said. Mountain lions are classified by the state as a “specially protected species,” according to the California Department of Fish and Wildlife.
Six populations in Southern California and the Central Coast are under consideration for a threatened designation. Though hunting the creatures for sport is banned in the state, those populations still face low survival rates due to high levels of humancaused mortalities, like car strikes, poisonings and “sanctioned depredation kills,” according to the Mountain Lion Foundation, a national nonprofit.
Elsewhere in the state, including the Bay Area, the mountain lion population is thought to be relatively stable, according to the California Department of Fish and Wildlife — but it notes in an online FAQ that the exact number is unknown, due to the difficulty of estimating an “elusive species” in such a large and geographically diverse state. Estimates over the past 40 years have ranged from 2,000 to 6,000 mountain lions statewide.
An effort to update estimated numbers has been underway for almost a decade, officials say. However, the Fish and Wildlife Department has not released a new population assessment.
Updated numbers could shed light on a trend noted in the UC Davis report that seems promising, but that Shilling found troubling — throughout California, the rate of mountain lions dying in collisions appears to have declined by about 10% over the past seven years.
“If traffic doesn’t change, and you have a downward trend in some road kill for a species, that indicates a downward trend in the population of that animal,” Schilling said. “If they’re not being killed as often, it’s because there’s not as many of them running around on the road.”
Mountain lions became a flash point last year in California’s housing debate, after Woodside — which borders the stretch of I-280 highlighted in the report — tried to argue that the entire city was mountain lion habitat in an effort to skirt state law aimed at easing the housing crunch. The city swiftly backed down after a rebuke from Attorney General Rob Bonta, who labeled the move illegal — and added that by restricting housing production in an already developed area, it could increase exurban sprawl, harming mountain lion habitat in the process.
Shilling noted one straightforward remedy for the perils of I-280 — building fencing, overpasses and underpasses, like the wildlife crossing over Highway 101 in Southern California, that would allow animals to safely cross, a solution that could pay for itself in savings from collisions, according to the report.
Nearly a decade ago, Shilling and other UC Davis researchers prepared a report for Caltrans funded by a grant from the transportation agency that examined wildlife collisions on I-280 and found that fencing would be a cost-effective way to reduce collisions. But that recommendation has not been acted on, Schilling said.
Caltrans did not respond directly to questions about Shilling’s previous report, instead issuing a statement saying that the agency is pursuing funding for wildlife crossing improvements like fencing, land bridges and underpasses along 280 and throughout the state.
“Caltrans Bay Area District is currently compiling an inventory of regional wildlife passage needs, and I-280 is one of those locations that will be considered and prioritized for future funding,” the statement said.
The UC Davis report noted that, with the passage of the Road Repair and Accountability Act of 2017, the state has budgeted more than $5 billion per year for transit and safety, and some of that has been allocated toward building wildlife crossings, which Shilling would like to see more of.
“There are myriad excuses for why ‘nothing can be done,’ lack of funding is not one of them,” the report states.
But “one or two wildlife crossings” alone isn’t enough, Shilling said — the problem comes down to the changes humans have made and continue to make to the environment, which means in his view that it’s up to humans to fix it.
For a mountain lion looking to cross from the protected areas west of I-280 to the hills on the other side of the freeway while also instinctually attempting to avoid humans, there are few options other than crossing the road itself, he said.
“Imagine how you would get to the other side, if you were a wild animal,” he said. “We’ve built the barrier. We’ve built them everywhere. So I think it’s our imperative to solve that problem for them.”