Herds over highways: Colorado’s largest wildlife overpass is now under construction above I-25

Deer at Little Book Cliffs northwest of De Beque on Colorado’s Western Slope
Hart Van Denburg/CPR News
Deer at Little Book Cliffs northwest of De Beque on Colorado’s Western Slope, Sept. 10, 2024.

Construction of the largest wildlife overpass in Colorado is underway across Interstate 25 in Douglas County. According to the Colorado Department of Transportation, it'll also be one of the largest in the U.S.

Located on the interstate between Monument and Larkspur, the Greenland Wildlife Overpass aims to provide a safe passage for large animals such as deer, elk, and pronghorn over six lanes of traffic. The bridge, expected to be finished in December, will be constructed with sloped entrances and covered in native grasses as an invitation for wildlife to use the crossing.

A drawing of a herd of elk crosses over a highway using a large grass covered bridge
Colorado Department of Transportation
Conceptual image of Greenland Wildlife Overpass showing a herd of Elk crossing over I-25

The overpass will connect 39,000 acres of habitat within the Douglas County Land Conservancy to more than one million acres of the Pike National Forest, which are each under long-standing conservation easements. 

Colorado has become a leader in constructing wildlife crossings, with over 100 structures, including overpasses and underpasses, present throughout the state, according to CDOT.

Rocky Mountain Wild

Deer walk through an underpass below State Highway 9. However, CDOT officials say larger animals like deer, elk and pronghorn prefer overpasses with clear sight lines over underpasses.

However, only three of the existing wildlife crossings are overpasses, which are used by large animals, who prefer open structures with clear sight lines. Large ungulates, especially the skittish pronghorn, don't use underpasses frequently, according to CDOT

Construction of the overpass is a part of the I-25 Gap project, which has focused on improving 18 miles of I-25 from Castle Rock to Monument, primarily through adding a toll lane in each direction. CDOT expects this overpass, along with three other new wildlife crossings and 28 miles of deer fencing, to decrease animal-vehicle collisions by 90 percent.

A rendering of an overpass over the highway with grass and animals crossing.
Colorado Department of Transportation
Conceptual rendering of Greenland Wildlife Overpass over I-25 between Monument and Larkspur