Why Wildlife Crossings Work: Banff's Proof and the World's Largest Crossing
The world's largest wildlife crossing is almost finished, and I can't stop thinking about a Canadian highway.
Just north of Los Angeles, the Wallis Annenberg Wildlife Crossing is being built over ten lanes of the US-101 freeway. The State of California expects it to be completed in fall 2026, and the project team calls it the world's largest wildlife crossing — the span over the freeway alone is about 250 feet long and 174 feet wide, now being planted with native shrubs so animals barely notice the traffic rushing below.
I care about this partly because I've seen the other end of the story. Driving the Trans-Canada Highway through Banff National Park, I kept passing wide, grass-covered bridges arching over the lanes — not built for cars, but for elk, bears, wolves, and cougars. Banff is where this idea grew up.
The science
Here's the science, and why it's more than a nice gesture. A busy highway harms wildlife in two ways: it kills animals outright, and — more quietly — it cuts a population into smaller, isolated pieces. Small, cut-off populations lose genetic diversity and grow more fragile over time. Crossing structures paired with fencing address both problems at once: the fence guides animals toward safe passages, and the passages knit the landscape back together so animals, and their genes, keep moving.
Banff's proof
Banff is the best long-term proof we have. Parks Canada reports the park now has 44 wildlife crossing structures — six overpasses and 38 underpasses — plus 82 kilometres of highway fencing. Since that system went in, wildlife-vehicle collisions have dropped by more than 80 percent overall, and for elk and deer alone by more than 96 percent. A genetic study led by biologist Michael Sawaya, published in Proceedings of the Royal Society B, went further: by analyzing bear hair snagged at the crossings, his team showed grizzlies and black bears were using them to reach mates on the far side, beginning to restore the gene flow the highway had cut off.
The two projects aren't strangers, either. One of the ecologists whose work informs the California crossing, Tony Clevenger, spent years studying the Banff structures. Data gathered patiently along a highway in the Rockies helped make the case for a bridge over one of the busiest freeways in the United States.
That's the part I find quietly hopeful. Conservation science is often slow and undramatic: cameras on posts, seasons of counting tracks and collecting hair. But it compounds. A monitoring program in Banff becomes a design manual for Los Angeles, which becomes a template for the next place that decides its wildlife deserves a way across.
So next time you're driving through Banff and spot a green bridge with no road on it, look closely. You're seeing one of the most successful conservation experiments on the continent — and a preview of what's arriving at a freeway near you.
Planning a park road trip with kids?
Long drives are part of every national park trip. I made the Screen-Free Road Trip Kit to turn the miles into part of the adventure: 35+ printable pages of road trip bingo, nature scavenger hunts, a Roadside Science Spotter, sketch prompts, and trip reflection pages for curious kids ages 7–12. Print it, pack it, and go.
Comments