Interstate 90 is the longest interstate highway in the United States. Spanning more than 3,000 miles, it connects Seattle in the west to Boston in the east. But it also serves as a massive concrete divide. For the animals who live to the north and south of the interstate, this road has absolutely wrecked their commute.

The U.S. Forest Service and the Washington State Department of Transportation have teamed up to develop a network of "critter crossings" in Washington – overpasses and underpasses designed to provide safe passage for wildlife.

The crossing project, with structures at areas identified where animals are likely to cross, spans 15 miles of I-90 near the Snoqualmie Pass in Washington, flanked by large chunks of what's primarily national forest land – habitat for all sorts of creatures great and small.

But if animals are protected on both sides of I-90, why does it matter if they're not connected? "Because you lose genetic variability," said Patty Garvey-Darda, a wildlife biologist with the Forest Service, "and gradually you start getting localized extinction, and populations get further and further apart, and smaller."

Around the country, most animals see a busy highway and turn around. A brave few might try to cross, but they're at risk of getting run over. A wildlife crossing is supposed to make that process far less treacherous. But there's no guarantee that if you build it, they will come. So, miles of fencing along the road serves to funnel animals towards crossing points. High concrete walls block headlights and dull the traffic noise.

"We wanna mimic the habitat on either side, native plants and everything, so that animals sort of don't even see the transition," said Garvey-Darda.

It worked. In 2022, cameras captured animals – including mule deer, elk and coyotes – using these crossings more than 5,000 times.

According to Brian White of the Washington DOT, the wildlife crossings in Banff, Alberta, Canada, were a success story to mimic. Banff's 38 undercrossings and six overcrossings along a section of the Trans-Canada Highway that cuts through Banff National Park have reduced wildlife collisions by 80 percent, and been used as a model for crossings worldwide. 

Back in the U.S., there are now around 1,500 wildlife crossing structures in 43 states. In Wyoming, pronghorn run across Highway 191. In Florida, panthers and alligators creep under I-75. They can be subtle; motorists may have no idea they're driving over moose in Montana or tunnels full of tortoises in Utah.

But it will be hard to miss the crossing currently being built not far from Los Angeles; once it's completed, in late 2025 or early 2026, the Wallis Annenberg Wildlife Crossing will stretch for more than 200 feet across 10 lanes of the 101 Freeway, which can see up to 400,000 vehicles a day. It will be the largest wildlife corridor in the country.

Beth Pratt, who serves as regional executive director for the National Wildlife Federation in California, said, "I think that's a real miracle, that over one of the busiest freeways in the world you're gonna be driving under it, and mountain lion, fox, might be walking over. Or a fence lizard, or a ground squirrel may have a family on top. That's a really hopeful project. And we do owe it to P-22."

P-22 was the celebrated mountain lion who roamed around L.A.'s Griffith Park. When he was younger, he somehow made it across two freeways, only to end up a lonely Hollywood bachelor until his death in 2022.

But even for the mountain lions who can find mates, the dates are a little too close to home, and biologists worry the small population here could soon go extinct. The crossing, which is estimated to cost $90 million, will expand the dating pool. That's important for all sorts of critters, even ones that aren't as obviously charismatic.

Back underneath I-90, Professor Jason Irwin and his team of Central Washington University students are focused on everything from toads to salamanders making use of an underpass. "It's really been fantastic to work in a project where they appreciate the little guy," he said.

There are also human lives at stake. There are approximately one million collisions involving large wildlife on America's roads each year, resulting in some 200 human deaths.

Last year, Transportation Secretary Pete Buttigieg announced a federal grant program awarding a total of $350 million to states looking to build crossings and improve safety.

• UC Davis study says animal crossings could save California billions

White has already seen a reduction in collisions where the crossings have been built.  "If you think about it that way, and you think about how many accidents didn't happen, these crossing structures pay for themselves pretty fast," he said.

And fewer road closures mean faster commutes for everyone.

Even though the crossing construction in Los Angeles has meant occasional slowdowns and lane closures, Pratt said the public has been able to stay focused on the benefits down the road.

"Wildlife crossings are something, it doesn't matter if you're a Republican or a Democrat, or what political affiliation – people really support them," she said. "I think there's very few people who don't get upset when they see a dead animal on the side of the road. So, I think that this is something that in a time where we agree on very little, we pretty much agree on wildlife crossings."

      
For more info:

• U.S. Forest Service
• Washington State Department of Transportation
• National Wildlife Federation
• Wallis Annenberg Wildlife Crossing (Annenberg Foundation)
• SaveLACougars.org

      
Story produced by Michelle Kessel. Editor: Joseph Frandino.