With This Bridge, Mountain Lions Don’t Have To Dodge Cars To Cross An 8-Lane Freeway

The bridge crossing California’s 101 would be the widest wildlife crossing in the world.


“L.A. traffic sucks–especially for the cougars. And no, I’m not talking about the housewives of Brentwood.” So says Rainn Wilson in a new video made to support a massive new bridge to help mountain lions and other wildlife cross eight lanes of traffic over the 101 freeway.


The 200-foot long bridge would help prevent crashes like the one that killed a 21-month old cougar when he tried to cross another nearby freeway in August. He was one of a dozen to be killed by cars since researchers started studying the tiny population left in the area in 2002.

More than just preventing car accidents, it’s a way to give the last large carnivore in the area the space it needs to survive. “When a freeway gets to be that big, with that much traffic, most animals don’t even try to cross it,” says Seth Riley, a wildlife ecologist with the Santa Monica Mountains National Recreation Area.

Clark Stevens/Raymond Garcia, Resource Conservation District of the Santa Monica Mountains

Relatively large swaths of open space still exist in places like the Santa Monica Mountains and Griffith Park, but because freeways act as barriers, mountain lions can’t roam far enough for the population to thrive.

“We know from the work we’ve done over the last 12 years or so that the Santa Monica Mountains by themselves are just not big enough for a viable population of mountain lions,” says Riley. “There’s really only room for a dozen or so adults.”

As the space to roam shrinks, so does genetic diversity, which is a requirement in the long-term for a species to maintain a healthy population. “The only place that was lower was in Florida Panthers,” he says. “That’s a population that virtually went extinct because of genetic diversity issues.”


The proposed bridge would connect the Santa Monica Mountains with the Simi Hills to the north, helping mountain lions, bobcats, coyotes, deer, and smaller animals like squirrels safely cross the road.

It’s designed to look like native habitat. “We’re trying to do everything we can to make it hospitable as possible,” Riley says. The bridge would be 165 feet wide–wider than any other wildlife crossing in the world–so it could be planted with local, drought-tolerant plants and trees. Sound walls would help deafen the noise from cars and block headlights.

“It doesn’t mean that there isn’t some stress for animals,” he says. “But we’ve seen that they’ve crossed the actual freeway itself in a couple of cases. And this would be a lot easier than actually trying to go over the freeway itself.”

For animals like mountain lions, the crossing could be enough to keep them from extinction. “Not every animal will find it,” says Riley. “But one thing that’s nice, from the point of view of genetics, you don’t need that many animals. One or two per generation can really make a huge difference.”

Supporters have been pushing for a crossing for more than a decade, but it’s only now getting close to reality. A new report from Caltrans evaluated the cost of the bridge–$30 million to cross the freeway, and as much as $60 million if it also crosses another nearby road. With government support, more paperwork, and enough cash, the bridge will go forward.


Ecologists considered a tunnel in the past, but there were several problems with that plan–the freeway would have to be shut down longer, and prey animals like deer would be afraid to cross underground. “The overpass is the best to maintain connectivity for a whole range of species,” Riley says.

The giant bridge could also be used by hikers or mountain bikers during the day, when animals are less likely to use it. And it would send a message to anyone driving below.

“101 is one of the busiest freeways in the world,” Riley says. “Everyone would see it as they drove along. It would really make a big and powerful statement about the fact that even here in one of the largest cities in the country, people really care about preserving wild land and preserving wildlife.

About the author

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley, and contributed to the second edition of the bestselling book "Worldchanging: A User's Guide for the 21st Century."