Colorado's giant wildlife overpass cuts I-25 animal collisions 91% in its first ten months

For decades, a stretch of Interstate 25 between Larkspur and Monument in Colorado killed roughly one animal per day. In the ten months since North America's largest wildlife overpass opened across that same corridor, drivers have struck two animals — a 91% drop that slightly exceeds what state engineers had predicted.

At 209 by 200 feet, the overpass near the Greenland exit in Douglas County anchors a broader crossing system that also includes five wildlife underpasses and miles of fencing designed to funnel animals toward the safe passages. Together, the system connects 39,000 acres of habitat on either side of the six-lane highway, closing a 3.7-mile gap between other crossings, according to CDOT.

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.— Chuck Attardo, CDOT Environmental Manager

When CDOT completed the structure in December 2025 — ahead of schedule and under budget — its own projections called for a 90% reduction in wildlife-vehicle collisions. The measured result after ten months came in a point better. Federal infrastructure funds covered $22 million of the cost and the state contributed $8 million, yet contractor Kraemer North America brought the project in at roughly $15 million, according to Attardo.

They pay for themselves in about 15 years because of all those accidents that they prevent, and so why wouldn't you do more of these?— Chuck Attardo, CDOT Environmental Manager

The overpass was designed with large, open sightlines specifically to attract elk and pronghorn — animals that instinctively avoid enclosed spaces. The design appears to be working for both. Camera footage captured a pronghorn crossing the overpass, the first confirmed crossing of I-25 by the species in 20 to 30 years, according to Lisa Schwantes, a regional communications manager for CDOT. Pronghorn are also using the underpasses, tracking data shows.

For decades, pronghorn going from Trinidad to Greenland were looking for a place to cross on I-25. And when we open this up, we have pronghorn on video using the overpass, and for the first time in decades they're coming over here to the west side.— Chuck Attardo, CDOT Environmental Manager

The crossing is not only serving the large animals it was built for. Biologists have documented bears, deer, coyotes, bunnies, northern leopard frogs — which carry protected status after dramatic population declines — and the federally threatened Preble's meadow jumping mouse using the system. Wildlife biologists piled wood into a pathway across the overpass deck specifically to give small mammals cover from coyotes, foxes, and hawks during the crossing.

We're not just focused on the big game species, but also on the smaller. This is an area where Preble's meadow jumping mouse, which is federally threatened, lives, and so Preble's also needs to get to the other side of I-25 too.— Brandon Marette, CPW wildlife biologist

We are thrilled. Wildlife overpasses and underpasses and funneling animals to have a safe path across the roads, it's been statistically proven that it's successful.— Bridget O'Rourke, spokesperson for Colorado Parks and Wildlife

The benefits extend to drivers. Fewer collisions mean fewer instances of law enforcement and maintenance crews closing lanes around crash scenes. CDOT data reported by the Colorado Sun show that travel delays along the corridor have fallen by about 9%.

The crossing was the final piece of the broader I-25 South Gap project, a five-year effort begun in 2018 to widen and improve safety on 18 miles of interstate between Castle Rock and Monument. A CDOT research report commissioned by the state, as cited by Colorado Politics, determined that wildlife-vehicle collisions fell 91% once the agency had put most of its planned mitigation system in place — a network that includes five underpasses and 14 miles of fencing running along each side of the interstate.

Building the Greenland overpass required cooperation among the Federal Highway Administration, CDOT, Colorado Parks and Wildlife, Douglas County, the Douglas Land Conservancy, and the Colorado Cattlemen's Agricultural Land Trust, which hold conservation easements on either side of the highway.

One of the most heartwarming moments for me was when CDOT sent me a picture of an elk mama taking her calf under I-25. All the hard work for six years all came to fruition in that one moment. That elk with her calf was just standing there in safety, getting to the other side of I-25.— Brandon Marette, CPW wildlife biologist

The success is already driving plans for six more crossing systems across Colorado. Among the sites under consideration, according to the Colorado Sun, are the westbound lanes of I-70 at East Vail Pass between Vail and Copper Mountain, I-25 just north of the New Mexico state border, US 160 east of Cortez, Colorado 40 west of Craig, and a location near US 287 south of the Wyoming border. Along Colorado 40 east of Empire, one planned project would become the first wildlife overpass built with Rocky Mountain bighorn sheep specifically in mind.

Funding for future projects will come from multiple directions. A recently passed state law is expected to generate roughly $3 million a year for wildlife mitigation — money Attardo said can serve as grant match for larger federal awards. Starting in January, Colorado drivers will also be able to opt into a $5 fee directed toward wildlife crossing construction, similar to the existing $29 Keep Colorado Wild pass, which has generated $146 million since launching in 2023, according to the Colorado Sun.

One challenge remains: vegetation on the overpass deck struggled to germinate during this year's drought, slowing efforts to make the structure more attractive to wildlife. CDOT plans to bring in new topsoil and reseed in 2027, according to CBS News.

Why it matters — The Greenland overpass is the first large-scale proof-of-concept for a statewide Colorado strategy that could be replicated at six more locations — and its financial and safety data give other states a concrete case for similar investments.

Reported by goodnewsnetwork.org, coloradosun.com, cbsnews.com, dougcosocial.com, coloradopolitics.com