The wildlife overpass under construction on Interstate 25 between Larkspur and Monument will be the “world’s largest bridge structure built for wildlife,” officials said in a release Friday as they marked the project’s halfway point. 

Measuring 200 feet wide and 209 feet long, the massive I-25 Greenland Wildlife Overpass will cover nearly an acre once completed. It will span six lanes of traffic, on a stretch of the interstate traveled by more than 100,000 vehicles each day, according to the Colorado Department of Transportation.

While significantly shorter than the half-mile-long Zanderij Crailoo Nature Bridge in the Netherlands, Colorado’s overpass is wider. It’s also wider than California’s Wallis Annenberg Wildlife Crossing, which is currently under construction and will span 10 lanes of traffic.

With the stretch of the interstate between Castle Rock and Monument averaging “one wild-life vehicle crash a day in the spring and fall seasons,” officials say the bridge is expected to reduce wildlife collisions by 90%.

There are already five nearby underpasses in the area, this bridge, however, will benefit elk and pronghorn in particular. Officials say both species prefer to cross “open structures that provide clear and open sight lines” instead of tunnels. Moose, bear, mountain lions, mule deer and smaller animals are expected to use the structure as well.

Greenland Wildlife Overpass may reconnect elk herds split since I-25 construction

During the next phase of the project, a bridge superstructure will be constructed over the girders, officials said. The work will include “pouring the concrete bridge deck and tying into abutments, building walls, grading slopes, preparing the soil and wildlife landscaping, and installing wildlife fencing,” according to the release. 

According to CDOT, signs will be posted to alert motorists of traffic impacts during instruction, including:

• Daytime and nighttime lane closures in both directions of I-25 
• Periodic nighttime Express Lanes closures on I-25
• Temporary lane realignments, narrowed lanes and reduced shoulders on I-25
• Reduced speeds through the work zone

The $15 million overpass is expected to be completed in December 2025.