Wildlife Crashes on Colorado’s I-25 Fell 91% Before the Big Overpass Even Opened

For years, the stretch of Interstate 25 between Larkspur and Monument, Colorado, was a hazard for anything with hooves. Now a study commissioned by the Colorado Department of Transportation (CDOT) has found that crashes between vehicles and wildlife there fell 91% in the study’s final year, after the state built most of a system of underpasses and fencing.¹

That matters for drivers and animals alike. Before the work, wildlife were involved in an average of 32 crashes a year on this section of highway. That made animal collisions its third most common type of crash, even though they are under-reported.¹

What the study actually measured

The 91% figure comes with an important detail. The study used crash and camera data from 2022 to 2024. That covers the five underpasses and the 14 miles of fencing on each side of the highway, but not the big new overpass, which opened later.¹ CBS Colorado also reported that the reduction came from the crossing system as a whole.²

Across the study period, wildlife collisions dropped about 85% a year on average, reaching 91% in the last year. Overall crashes on the corridor fell 20%, likely helped by roadway changes as well as the wildlife work.¹

The result landed almost exactly where officials aimed. When the overpass opened, CDOT Executive Director Shoshana Lew said the crossing system was expected to cut wildlife-vehicle crashes by 90%. Gov. Jared Polis pointed to the 91% result as an example of smart infrastructure.⁵

The final piece: a bridge with no cars allowed

The Greenland Wildlife Overpass opened in December 2025 near the Greenland exit. It spans all six lanes of I-25 and measures about 209 by 200 feet, which makes it less a bridge than a small, nearly square field hovering over traffic.²

CDOT calls it the largest wildlife overpass in North America. It may not hold that title long. Colorado Politics notes that California’s Wallis Annenberg Wildlife Crossing is set to surpass it when it opens this winter.¹

The overpass fills a 3.7-mile gap between other crossings and connects about 39,000 acres of habitat. It closed the last opening in an 18-mile system of crossings and fencing along what CDOT calls the I-25 South Gap corridor.⁴

Before all this, the interstate was a barrier animals had to risk their lives to cross. “It was an effective wall that they had to play Frogger and try to get across,” Colorado Parks and Wildlife biologist Brandon Marette told CBS Colorado.²

Who’s crossing

CDOT says the first elk showed up on the overpass cameras in June. Since then, cameras have recorded pronghorn, mule deer, black bears and mountain lions using it.⁴

“Based on the video feed that we’re collecting, huge success. We’re seeing elk herds cross the bridge. We’re seeing pronghorn for the first time in decades cross over to the west side of I-25 because of the bridge,” CDOT environmental manager Chuck Attardo told CBS Colorado.²

Smaller residents got attention too. Biologists piled brush and logs along the overpass so little animals have somewhere to hide from predators. The area is home to the federally threatened Preble’s meadow jumping mouse and to northern leopard frogs.¹²

Still growing, still being studied

Data on how the overpass itself is performing is still being collected.¹ This year’s drought slowed the plants meant to cover it, and CDOT plans to bring in new topsoil next year. A research team led by Julia Kintsch is gathering elk genetic data to see whether the reconnected habitat increases genetic diversity, with first results expected in spring 2027.¹²

Contractor Kraemer North America finished the overpass ahead of schedule and under budget. Attardo says crossings like this pay for themselves in about 15 years through prevented accidents.²

CDOT hopes to build similar crossings when federal grants allow. Candidate sites include Raton Pass, US-40 near Empire and near Craig, Highway 160 near Mesa Verde, East Vail Pass, US-287 near Fort Collins, and near Boulder.²