Beginning Monday, a portion of Los Angeles County’s 101 Freeway will undergo nightly closures for several weeks to facilitate the construction of what’s dubbed as “the world’s largest wildlife crossing.” This expansive crossing, spanning 10 lanes of highway, aims to ensure safe passage for wildlife, particularly mountain lions, between the Santa Monica Mountains and the Simi Hills of the Santa Susana mountain range.

Initiated by the California Department of Transportation (Caltrans) in April 2022, the project is anticipated to reach completion in 2025. Once finished, the bridge will be camouflaged with soil and indigenous plants to seamlessly blend into its natural surroundings. Highways like the 101 often act as barriers to wildlife, impeding their movement and genetic diversity.

Caltrans asserts that this crossing will be the largest of its kind in the United States, while the project’s official website claims it will hold the title for the world’s largest, serving as a global model for urban wildlife conservation.

The closures will commence with the shutdown of all southbound lanes in the Agoura Hills vicinity from Cheseboro Road to Liberty Canyon Road, lasting approximately five hours starting at 11:59 p.m. PT on weekdays. As construction progresses, closures will transition to northbound lanes.

“These closures prioritize public safety as crews install girders over the freeway for the Wallis Annenberg Wildlife Crossing, a vegetated bridge across Highway 101 aimed at reestablishing wildlife corridors,” stated Caltrans.

Weather conditions or operational exigencies may prompt schedule adjustments, with detours via local streets being provided.

During the project’s inception, Caltrans reported receiving over 5,000 individual contributions for its construction. The crossing is named after the president and CEO of the Annenberg Foundation, a family foundation supporting various non-profits.

“We can coexist side by side with all kinds of wild instead of paving it over and choking it off,” said Wallis Annenberg at the groundbreaking ceremony. “It is about bringing more attention to an ingenious solution so urban wildlife and ecosystems like this one cannot only survive, but thrive.”

The wildlife crossing is expected to grant access to habitat for various species including coyotes, bobcats, deer, snakes, lizards, toads, and even ants. However, according to the National Park Service (NPS), mountain lions, particularly cougars, will reap significant benefits from the crossing.

In Los Angeles, mountain lions have been confined to what the NPS describes as a freeway-encircled “urban island,” leading to inbreeding. The NPS further notes that genetic analyses indicate mountain lions in the Santa Monica Mountains possess notably low genetic diversity compared to other populations.

The project’s website emphasizes that the crossing will play a crucial role in mitigating this genetic decline by enabling mountain lions from north of the Santa Monica Mountains to traverse into the range, while facilitating the dispersal of animals residing south of the freeway out of the area.

Notably, the famous mountain lion P-22, born in the Santa Monica Mountains, managed to cross two busy Southern California highways before becoming isolated in Griffith Park, a sprawling urban area in Los Angeles. Unfortunately, P-22 was euthanized in late 2022 due to severe injuries consistent with a vehicle collision and chronic conditions impairing his ability to survive in the wild, as reported by the California Department of Fish and Wildlife.