Colorado’s I-25 wildlife overpass cuts animal collisions by 91 percent over nine months

If you drive I-25 between Castle Rock and Monument, you’ve driven under it, a massive dirt-covered bridge spanning all six lanes of the interstate near the Greenland exit. It doesn’t look like much from the road, and that’s the point. It wasn’t built for you. It was built for the elk.

Nine months after opening last December, the I-25 Greenland Wildlife Overpass is being called a massive success. The numbers are in: the wildlife mitigation system, which includes the overpass, five underpasses and miles of fencing to guide animals to the crossings, has reduced wildlife-vehicle collisions in the corridor by 91 percent. Before the system was built, that stretch of highway between Larkspur and Monument averaged one animal-vehicle crash per day during peak migration in spring and fall. “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. Now, cameras mounted on the bridge are capturing elk herds, mule deer, black bears, mountain lions and, for the first time in decades, pronghorn crossing over to the west side of I-25. “We’re seeing pronghorn for the first time in decades cross over to the west side of I-25 because of the bridge,” said CDOT Environmental Manager Chuck Attardo. “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.”

The overpass itself is a beast, 200 feet wide, 209 feet long, covering nearly a full acre and held up by 76 steel girders. It’s the single largest bridge structure built for wildlife in North America and one of the largest in the world. It was designed specifically for elk and pronghorn, which avoid tunnels and enclosed underpasses because they can’t see through them and their antlers don’t fit. The overpass gives them wide open sight lines in every direction, with gradually sloped entrances that make it feel less like a bridge and more like a natural ridgeline. CDOT is also adding more vegetation to make it even more inviting. The $15 million project was completed in less than a year, ahead of schedule and on budget, with the bulk of the funding coming from a federal grant through the U.S. DOT’s Wildlife Crossings Pilot Program. It connects 39,000 acres of Douglas County Land Conservancy habitat to more than one million acres of Pike National Forest, completing an 18-mile crossing network between Colorado’s two biggest cities.

The return on investment is staggering. According to the Pew Research Center, each prevented deer collision saves about $19,000. Each elk collision saves $73,000. Each moose, $110,000. At one crash per day, the math basically pays for the entire bridge in two to three years. More than 100,000 vehicles travel that stretch of I-25 every day, and now they’re doing it without dodging a 700-pound elk in the dark.