The passageway under I-25 near Monument doesn’t look like much—to a human, that is. But for the many animals who call this rural stretch south of Denver home, including black bears, elk, and mule deer, the rocky floor of the underpass represents something of a lifeline. The path, along with four others completed last fall along I-25, allows wildlife to cross the busy highway without risking a deadly collision with a car or truck.

Preventing such crashes, which are reported 4,000 times a year in Colorado, according to the Colorado Department of Transportation (CDOT), is exactly what wildlife corridors are supposed to do by safely connecting animal habitats that have been divided by human activities or structures (especially roads). Also called habitat corridors, these passageways can be as extravagant as the vegetated land bridge arching over the Bukit Timah Expressway in Singapore or as simple as a small drainage tunnel under a street, and usually include roadside fencing to discourage animals from stepping onto the pavement.

A wildlife corridor under I-25
One of the wildlife corridors recently built under I-25. Courtesy of Bill Vogel/CPW

Whether eye-catching or simplistic, wildlife corridors are remarkably effective. The network of bridges and tunnels in Canada’s Banff National Park, for example, have reduced wildlife-vehicle collisions by 80 percent since they were installed in the 1980s. After CDOT built a land bridge on Highway 9 near Kremmling in 2016, accidents in the area dropped by 90 percent. Those are attractive numbers in a state where more than 250 people are hurt each year when animals and automobiles tangle, accidents that cost Colorado drivers $80 million in property damage, injuries, and, occasionally, fatalities.

Each data point represents a compelling reason to put more wildlife corridors in place. And CDOT wants to, says Andrew Karsian, a state legislative liaison who works to advance the department’s legislative agenda at the Colorado State Capitol. But between design and construction, not to mention the sometimes years-worth of research that goes into determining the best place for the corridor, building such passageways can be expensive. The corridors under I-25, for example, cost roughly $20 million. “Just maintaining the existing roads we have is a full-time job, and CDOT runs a deficit on that,” Karsian says. “Let alone building all of the new infrastructure we need in the state because of the growing population.”

A bill recently introduced in the state Senate, Safe Crossings For Colorado Wildlife And Motorists, aims to fix the price tag problem. SB22-151, which was approved by the Transportation & Energy Committee Tuesday, would create a $25 million cash fund devoted to building habitat corridors. The hope, says state Senator and sponsor Jessie Danielson, is that earmarking millions specifically for corridors would help the state access even more funding made available through the Infrastructure Investment and Jobs Act, signed by President Joe Biden into law last November. The massive infrastructure bill sets aside $350 million to be given as grants over the next five years to states, municipalities, and tribal nations building wildlife corridors.

Danielson and other proponents of SB22-151, including environmental groups like nonprofit Conservation Colorado, believe having a state source of matching funds will help Colorado leverage more of that $350 million. “We want to make sure Colorado is prepared and at the front of the line to receive that federal money,” Danielson says.

All that money would help Colorado achieve the goals set forth by the Colorado Wildlife and Transportation Alliance, a partnership between CDOT, Colorado Parks and Wildlife (CPW), and others (such as nonprofits and biologists) that began in 2018. The Alliance has helped CDOT and CPW share data and conduct studies to figure out where roadways are interfering with wildlife migration patterns, especially the pathways herd animals use to access their winter ranges. “You see a decline in herd health when animals can’t reach areas with enough food to get them through the cold months,” says Michelle Cowardin, wildlife movement coordinator with CPW.

Using that data, CDOT has added 25 different projects to its list of desired wildlife corridors in the state. One of them, a proposed trio of structures on East Vail Pass, has been studied extensively by Summit County Safe Passages, a nonprofit made up of officials with CPW, as well as representatives from the Denver Zoo and several ski resorts and towns in Summit County. The project would connect southern and northern portions of the White River National Forest that have been separated by I-70.

A deer near East Vail Pass
A deer photographed by a remote-triggered camera near East Vail Pass. Photo courtesy of Denver Zoo and Rocky Mountain Wild

East Vail Pass is one of the few areas in Colorado where the rare Canada lynx breeds. But for these carnivores and other animals, I-70 is like the Berlin Wall, says Stefan Ekernas, Rocky Mountain/Great Plains program director with the Denver Zoo and member of Summit County Safe Passages. A series of cameras set up by Ekernas and his team found that the paved ribbon—and the 23,000 vehicles that use it each day, on average—acts as a buffer to animals on either side of the road. Animals that do try to cross often don’t make it. Hundreds were hit in 2021, including four lynx.

CDOT supports Summit County Safe Passages’ idea for a land bridge and two underpasses, but it currently doesn’t have the $21 million the project requires. The passage of SB22-151 could fix that, says Ekernas, though the bill will have to make it through the Senate Appropriations Committee before being discussed—and voted on—by the full state Senate. “There are a lot of problems in this world that don’t have clear solutions,” Ekernas says. “And wildlife-vehicle collisions are not one of those problems.”

Angela Ufheil
Angela Ufheil
Angela Ufheil is a Denver-based journalist and 5280's former digital senior associate editor.