Colorado Gambled on North America's Largest Wildlife Overpass, and It's Working

Interstate 25 between Larkspur and Monument, Colorado, cuts through 39,000 acres of wildlife habitat . It's home to animals as massive as moose and elk down to tiny northern leopard toads. Crossing the 6-lane freeway used to be dangerous for any animal or human. Ten months ago, cars struck animals at least once per day on average.

Not anymore.

Civil engineers teamed with biologists to construct a $15 million “wildlife overpass” system across the highway. The project features a 209-foot bridge over the road and five tunnels beneath the pavement. It also uses a span of fences to steer animals to the safest routes across. It's the largest such project in North America. The project was finished in December 2025. Since then, the system has reduced the number of animals hit by cars by 91%, a recent study found.      

“We are thrilled,” Bridget O’Rourke told The Colorado Sun. She's a spokesperson for Colorado Parks and Wildlife. “It’s been statistically proven that it’s successful,” she added. 

The measures have prevented all but two collisions this year. It has also allowed traffic to flow more freely. Data from the state shows that travel delays on I-25 have decreased by 9% this year.   

Colorado plans to build six more wildlife bridges in the state in coming years. Other states are doing similar projects. A $115 million crossing in California will surpass the I-25 crossing as the largest in the US by a single foot. It will span across 10 lanes of the US 101 highway. The crossing is due to open on December 2.   

Reflect: Describe a place in your community where people and animals share space. How could it be designed to work better for both?