A decades-long project to open the world’s largest wildlife crossing across a 10-lane Southern California freeway is almost complete.
The Wallis Annenberg Crossing links critical habitats on both sides of the 101 Freeway in the Santa Monica mountains about 10 miles north of Malibu. The freeway, and nearby development, have essentially trapped populations of cougars, mule deer, bobcats and desert cottontail rabbits on either side, putting them at risk for birth defects and decreasing their habitat.
When completed next year, the overpass will allow all manner of wildlife to freely cross over one of the nation’s busiest highways, blissfully unaware of the thousands of vehicles speeding underneath. It’s the world’s largest crossing of its type, according to the Annenberg Foundation.
A major milestone was reached this week when workers began pouring what will eventually be 6,000 cubic yards of soil on top of the overpass. Crews will begin planting close to 5,000 native plants in May.
A bridge was first proposed for the area in 1990. Funding efforts began in 2014 and construction began in 2022.
To create the pathway, the project features a gently sloping overpass that is 165 feet wide and 200 feet long. It is designed to look like natural habitat and will be landscaped with native plants, a living garden that will entice animals to cross where it’s safe.
Even before it opens, the project seems to be attracting wildlife. In May of last year, urban wildlife scientist Travis Longcore was visiting the crossing site with students and observed a barn owl following the bridge across. For the first time since the highway was opened in 1926, there was a dark corridor over the freeway that the owl could follow, he said.
Why do animals need to cross the freeway?
The spot where the crossing is being built is one of few places left that has natural habitat on both sides of the 101 freeway The highway’s eight lanes constitutes a dangerous barrier for wildlife.
Cougars especially cover large ranges searching for food and mates. According to the National Parks Service, crossing the highway is the number one cause of death for the big cats, also known as mountain lions and pumas. Declines in their genetic diversity, due to being broken into small, isolated populations by freeways and buildings, have led researchers to fear they could go extinct within the next 50 years.
Humans benefit from the crossings too. Research by the Federal Highway Administration estimated that collisions between large animals, cars and trucks killed about 200 people and caused more than 26,000 injuries a year.
The first layers of soil being installed on the Wallis Annenberg Wildlife Crossing on March 31, 2025 in Agoura Hills, California.
Who’s paying for the crossing?
The crossing is estimated to cost a total of $92 million, with the majority of the money coming from non-profits and private donations.
It is part of a public-private partnership between the California Department of Transportation and multiple conservation and wildlife groups, including the National Wildlife Federation, the Annenberg Foundation, the state Wildlife Conservation Board and hundreds of small donors from all around the world.
Do animals really use wildlife crossings?
Wildlife crossings that allow animals, snakes, frogs and other species to safely cross roadways have been quite successful around the world.
Built as bridges, underpasses and culverts, studies have shown they can significantly decrease collisions, saving animals and protecting motorists.
According to the Pew Charitable Trusts, a crossing along State Highway 9 in Colorado reduced animal/vehicle collisions by 90% from 2015 to 2020. In Oregon along U.S. 97 near Lava Butte, collisions decreased by roughly 85% during a 2015-17 monitoring period.
Florida has more than 60 such crossings, to protect panthers, alligators, bears, bobcats and deer.
Robert Rock, of Rock Design and Associates, is seen working as the first layers of soil are placed on the Wallis Annenberg Wildlife Crossing on March 31, 2025 in Agoura Hills, California.
In Washington State, the Snoqualmie Pass East wildlife crossing has recorded more than 8,000 elk, 13,000 deer, 3,200 coyotes and 6 cougars crossing since 2014. The state posts periodic videos of animals making use of the crossing, including deer, rabbits, coyotes and otters.
A camera at a wildlife underpass in the Santa Cruz mountains caught a bobcat using the pathway.
The new Southern California crossing has already inspired wildlife lovers, including 2023 a group of enthusiasts who built a Lego model of the crossing, which they’ve asked the Lego company to transform into an actual Lego set that could be sold to the public.
This article originally appeared on USA TODAY: World’s largest wildlife crossing almost finished in California