Colorado's green wildlife bridge helps cut highway collisions by 91%

A grass-covered bridge spanning six lanes of a busy US highway is helping wildlife cross safely between habitats, while a wider network of crossings and fences has cut animal-vehicle collisions by 91% along a stretch of Interstate 25 in Colorado. The Greenland Wildlife Overpass, completed in December 2025, connects 39,000 acres of habitat near Larkspur and Monument, south of Denver. The $15 million structure is designed primarily for large animals such as elk and pronghorn, which often avoid enclosed tunnels. It forms part of an 18-mile wildlife-mitigation system that also includes five underpasses and fencing to guide animals away from traffic. State officials say the results offer a promising example of how road infrastructure can protect wildlife while making highways safer for motorists.

Colorado's giant green wildlife bridge over Interstate 25

The Greenland Wildlife Overpass is located near the Greenland interchange in Douglas County, between Larkspur and Monument. Built by the Colorado Department of Transportation (CDOT), it spans six lanes of Interstate 25, a major route connecting Denver and Colorado Springs. The bridge measures 200 feet wide and 209 feet long, covering approximately 41,800 square feet. Its surface is layered with soil and vegetation, while its broad, gradually sloping entrances are designed to encourage animals to approach and cross naturally. The structure was completed in December 2025, closing a 3.7-mile gap between existing wildlife crossings along the highway. It connects habitats used by elk, pronghorn, mule deer, black bears and other animals. According to CDOT, the crossing forms part of a wider network designed to reduce wildlife-vehicle collisions and maintain movement between natural habitats separated by the interstate.

Wildlife-vehicle collisions fell by 91%

A state-commissioned study found that wildlife-vehicle collisions along the I-25 South Gap corridor fell by 91% in the final year of the study period. The reduction followed the installation of most of the area's wildlife-mitigation infrastructure, including underpasses and fencing. The corridor previously experienced an average of about one wildlife-vehicle collision per day during periods of high animal movement in spring and autumn. Seasonal migrations bring animals across the landscape as they move between feeding areas and other parts of their ranges. The research examined collision trends from 2022 to 2024. During that period, the average annual reduction was approximately 85%, reaching 91% in the final year. The findings indicate that the wider crossing system has significantly improved safety. However, the overpass itself was completed in December 2025, after the study period, so the 91% figure cannot be attributed solely to the new bridge.

Why elk and pronghorn need a bridge instead of a tunnel

Large animals such as elk and pronghorn can be reluctant to enter enclosed passages. Tunnels may restrict their sightlines and movement, while the size of an animal's antlers can make narrow structures particularly unsuitable. The Greenland overpass offers a broad, open route across the highway. Its vegetation-covered surface and gradual approaches are intended to resemble the surrounding landscape, making the crossing more inviting to animals. The wider system complements the bridge with five underpasses that provide alternative routes for wildlife, including smaller species. Fencing along the highway helps guide animals towards these designated crossings rather than allowing them to enter traffic lanes. Together, the measures address two related problems: the risk of collisions and the fragmentation of habitats by major roads.

Elk and pronghorn have begun using the crossing

Wildlife cameras have recorded elk herds crossing the overpass, providing early evidence that the structure is being used by the animals it was designed to accommodate. Pronghorn have also been filmed crossing to the western side of I-25. State officials have described these sightings as particularly significant because the highway had long restricted their movement through the area. Monitoring has also recorded smaller wildlife, including rabbits and northern leopard frogs, using the crossing area. The project includes features intended to provide smaller animals with shelter from predators while they move across the exposed bridge. These observations show that the structure is functioning as a wildlife passage. Researchers are continuing to investigate whether it will also help reconnect animal populations that have been separated by the highway.

The $15 million project connects 39,000 acres of habitat

The Greenland overpass cost $15 million to construct, with federal funding providing the bulk of the support through the US Department of Transportation's Wildlife Crossings Pilot Program. The project was developed through cooperation between CDOT, the Federal Highway Administration, Colorado Parks and Wildlife, Douglas County and conservation partners. The crossing connects approximately 39,000 acres of habitat on either side of I-25, with the surrounding wildlife landscape linked to more than one million acres of the Pike National Forest. The overpass also completes a wildlife-crossing network along an 18-mile section of the interstate between Castle Rock and Monument. More than 100,000 vehicles travel through this corridor each day, making the separation between road traffic and animal movement an important safety concern.

Researchers will study whether the bridge reconnects wildlife populations

Reducing collisions is only one measure of the project's success. Researchers also want to understand whether the crossings help animals move between previously separated populations and whether that movement improves genetic diversity over time. Scientists are collecting baseline genetic information from elk populations on both sides of I-25. Comparisons over the coming years are expected to help determine whether the animals are mixing and whether the crossings are improving connectivity between populations. Initial genetic results are expected in spring 2027, with longer-term monitoring needed to assess the effects on wildlife populations. The distinction is important because camera footage can demonstrate that animals use a crossing, but it cannot by itself establish whether populations are becoming more connected or genetically diverse.

Colorado's wildlife crossings offer a model for safer roads

The Greenland Wildlife Overpass illustrates how transport infrastructure can be designed to accommodate animal movement instead of forcing wildlife to cross busy roads at dangerous points. The decline in collisions across the I-25 corridor suggests that a coordinated system of overpasses, underpasses and fencing can benefit both motorists and wildlife. Fewer collisions can mean less risk of injury, reduced vehicle damage and safer movement for animals travelling between habitats.