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Most hazardous highway: Peninsula's I-280 listed as deadliest in California for wildlife

University of California, Davis, report on roadkill urges legislators to take action
A stretch of Interstate 280 between Cupertino and San Bruno has been found to be the most hazardous for wildlife in the state.

More wildlife have been killed by vehicles along Interstate 280 between Cupertino to San Bruno over the past five years than in any other stretch of highway in the state, according to a new report by University of California, Davis.

The Road Ecology Center of UC Davis released a report on roadkill hotspots on California highways Wednesday, based on 44,000 wildlife-vehicle collisions from California Highway Patrol and 65,000 reports sent into the California Roadkill Observation System between 2009 and 2020.

According to the report, the 31-mile stretch along the Peninsula has racked up an estimated $5.8 million in damage annually.

Wildlife-vehicle collisions are defined as incidents in which animals cross roadways and pose a threat to driver safety, the report states. In such incidents, the driver may get injured or the car may be damaged from hitting an animal or swerving to avoid them. In addition, busy intersections can severely impact the wildlife populations that surround them.

The problem of wildlife-vehicle collisions is significant, the report states. Within the past five years, 302 mountain lions were involved in reported crashes. The report notes that this figure does not represent all mountain lions killed on highways and should only be considered as the minimum, as there is no formal requirement for residents to report roadkill incidents.

A new report reveals the deadliest stretches of Bay Area highways for wildlife. Courtesy UC Davis Road Ecology Center via Bay City News

The California Department of Fish and Wildlife is currently reviewing mountain lions as a potential candidate under the California Endangered Species Act and already has conservation plans to protect the 2,000 to 3,000 wild cats still living in the states. 

"Like most species at the top of the food web, mountain lions are especially vulnerable to (being struck by a vehicle) because they move around a lot and cross roads and highways. Mountain lions are important ecologically because they are the only large, widespread predator in most California ecosystems," reads the report. "They are also important socially, with great interest in their well-being in southern California and Bay Area urban regions."

The report also notes that roadkill incidents should not only be framed as an environmental issue, as these collisions can pose a real economic impact. The report estimates that wildlife-vehicle collisions cost state residents $1.1 billion to $2.2 billion within the last five years.

By identifying dangerous stretches of highway, the study aims to assist Caltrans and other transportation agencies in developing strategies to lessen roadkill. Some solutions with the best success rates include reducing speed limits in areas where plenty of wildlife live and building fencing or passageways for animals to safely cross above or below the highway, according to the report.

"Wildlife-vehicle collisions continue to be an under-recognized and under-reported threat to wildlife populations and to drivers in certain areas," the report states. "Even common species like mule deer may be experiencing unsustainable levels of mortality. The state should spend its ample transportation funds to solve this traffic safety and sustainability issue."

So how much would it cost to implement these mitigation strategies? Less than what wildlife-vehicle collisions have already cost the state in the past 10 years, the report estimates.

Fencing in 1,275 miles of high-risk highway would take a little over $175 million, meaning the reduced value of crash costs would exceed mitigation efforts in 10 years, according to the report.

But the report calls on legislators to take concrete steps to quickly invest in projects that reduce wildlife-vehicle collisions by using transportation funds, not limited wildlife, parks and environmental budgets.

Additionally, Road Ecology Center researchers encourage Californians to report roadkill sightings at to contribute to more accurate data analyses.

"Monitoring wildlife movement and mortality is critical for improving wildlife connectivity and survival of wildlife species in the face of the combined threats they face, such as transportation systems, climate change, rodenticides and habitat loss," the report summarizes.

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