Heavily trafficked roads act just like a giant wall, blocking wildlife from safely moving across. Highways can cause fatal collisions for people and animals, and present conservation challenges as well.
That’s a problem when you’re trying to get separate populations of grizzly bears to connect. Now, new research is identifying high-traffic roads that can make it impossible for bears to cross.
Road ecologist Marcel Hujiser studies how roads impact wildlife movement and ways to reduce wildlife-vehicle collisions.
“We know that when traffic volume is above 100 vehicles an hour, it is very unlikely that a grizzly bear gets to the other side of the road,” Hujiser says.
Hujiser is the the lead author of a new report in collaboration with the Yellowstone to Yukon Conservation Initiative looking at where wildlife are hit most on roadways in western Montana.
“We identified road sections that have a relatively high concentration of collisions, and then there's a conservation aspect of the work that is described in the report,” Hujiser says.
He then overlaid that collision info with data from state and federal biologists on grizzly bear movement. Grizzly populations in Montana exist in five distinct recovery zones: the areas surrounding Yellowstone and Glacier National Parks, the Cabinet Yaak, and the Bitterroot ecosystem.
“Now we can see where grizzly bears have a problem if they are to move, say, between the Northern Continental Divide ecosystem to the Bitterroot,” Hujiser says.
Courts have repeatedly ruled that bears cannot be removed from the Endangered Species List, and returned to state-level management, without gene flow. That’s a fancy term for bears moving freely from one recovery zone to another. Currently, that’s most likely to happen between the two biggest populations surrounding Yellowstone and Glacier.
“The shortest distance between those occupied ranges is essentially east of Butte, between Butte and, say, Cardwell,” Hujiser says.
Hujiser says building overpasses at sites like Homestake Pass, would have the biggest impact for grizzly movement.
Interest in wildlife crossings is growing. State laws passed in 2025 established a subset of marijuana tax revenue to go towards crossings, and the development of a specialty crossing-specific license plate to help fund the work.
The funding isn’t enough to build crossings everywhere they’re needed, but Hujiser says this money, combined with the research, is a good start.
