Colorado Built A Grass Bridge Over A Six-Lane Highway For Wildlife. Animal Collisions Dropped 91%
The I-25 Greenland Wildlife Overpass, a 200-foot-wide, 209-foot-long soil-and-grass bridge spanning all six lanes of Interstate 25 between Larkspur and Monument in Colorado, opened in December 2025 as the largest wildlife overpass structure in North America, built to give elk, mule deer, pronghorn, black bears, mountain lions, and dozens of other species a way to cross a highway that carries more than 100,000 vehicles per day without being struck by traffic. In the roughly ten months since it opened, state officials have recorded just two wildlife-vehicle collisions along the same stretch of road. In the five-year period from 2013 to 2017, drivers struck nearly 200 animals on that same stretch, including 119 deer, 18 black bears, 10 mountain lions, and one moose. During peak migration periods in spring and fall, approximately one deer was hit each day. The overpass, five wildlife underpasses, and 14 miles of guiding fences that make up the full crossing system have together reduced wildlife-vehicle collisions in the corridor by 91 percent, according to Colorado Governor Jared Polis's office, exceeding the 90 percent reduction that state transportation officials projected when the structure opened. The $15 million overpass was backed in part by a $22 million federal grant and was completed by contractor Kraemer North America after six years of coalition-building between the Federal Highway Administration, the Colorado Department of Transportation, Colorado Parks and Wildlife, Douglas County, and two land conservation organizations.
The results have been visible in ways that go beyond the collision statistics. Trail cameras mounted on the overpass have captured elk herds, mule deer does with fawns, bears, and mountain lions using the crossing. The most striking footage has been of pronghorn, a species that had not been documented crossing to the west side of I-25 in decades because the highway had effectively severed their migration corridor. Pronghorn are among the most committed long-distance migrators in North America, traveling hundreds of miles between seasonal ranges, but unlike many ungulates they are reluctant to jump fences or barriers and had been cut off from roughly half of their historical habitat by the interstate. The overpass connects 39,000 acres of wildlife habitat on both sides of the highway and has allowed the east and west elk herds, which had been reproductively isolated from each other since the highway divided them generations ago, to begin intermixing again. Colorado Parks and Wildlife biologist Brandon Marette, whose trail camera captured an elk and her calf standing on the overpass, described the moment simply: she was just standing there in safety, getting to the other side of I-25. CDOT environmental manager Chuck Attardo noted that a crossing of this scale pays for itself within approximately 15 years through the cost savings from prevented collisions, emergency responses, and traffic delays. The two collisions recorded in ten months, compared to a historical average of more than 32 annually, suggest the timeline may be shorter than that.
