Drivers on Colorado's Interstate 25 used to hit a wild animal about once a day. In the ten months since North America's largest wildlife overpass opened above the highway, they've hit two.

  • 91% drop in wildlife-vehicle collisions
  • 209-by-200-foot bridge, plus five underpasses and miles of fencing
  • 39,000 acres of habitat reconnected on either side of the highway
  • $15 million price tag, built in under a year, ahead of schedule

A Highway That Interrupted Everything

The stretch of I-25 between Larkspur and Monument cuts straight through territory where elk, mule deer, pronghorn, black bears and mountain lions have moved for generations. More than 100,000 vehicles cross it every day, and for decades the six-lane road was simply a wall.

That changed in December, when the I-25 Greenland Wildlife Overpass opened as the single largest bridge structure built for wildlife in North America. It spans all six lanes, its surface covered in dirt and native vegetation so animals barely notice they're crossing a highway at all.

What the Data Actually Shows

The Colorado Sun reports that state wildlife managers and transportation officials have confirmed the drop by tracking roadkill and collision reports along the corridor since the crossing opened. The overpass was built for big game like elk and pronghorn, which prefer wide, open structures — but trail cameras have also caught bunnies and northern leopard frogs using it.

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

In June, biologists confirmed something that hadn't happened in 20 to 30 years: a pronghorn safely crossed I-25 at this location. Pronghorn are notoriously reluctant to use underpasses, so the open-air overpass gave the herd a route it had been missing for decades.

A System, Not a Single Bridge

The overpass is only one piece of a larger network. Five wildlife underpasses and fencing funnel animals toward safe crossing points along the corridor, part of the broader I-25 South Gap project that upgraded 18 miles of highway from Castle Rock to Monument.

The payoff extends beyond animal lives. Fewer collisions mean fewer injured drivers, less traffic diverted for crash cleanup, and travel delays along the corridor down roughly 9%. Colorado State Patrol troopers and CDOT maintenance crews track every incident, from elk-sized crashes to smaller animals like foxes and raccoons.

What's Next for Colorado's Wildlife

Six more crossing systems are already in the design phase, including the first overpass built specifically for Rocky Mountain bighorn sheep, planned for Colorado 40 east of Empire. Other projects target I-70 near Vail Pass, I-25 close to the New Mexico border, and sections of U.S. 160 and U.S. 287.

Starting in January, Colorado drivers will be able to opt into a $5 annual fee dedicated to funding future wildlife crossings, similar to the existing $29 Keep Colorado Wild pass that has already generated $146 million since 2023.

"I think we just have to be aware that the Colorado human population is increasing and we are encroaching on wildlife habitat," O'Rourke said. For one stretch of I-25, at least, the animals finally have their own way through.