How Colorado's Wildlife Mitigation Efforts—Including the Largest Animal Crossing Overpass in North America—Are Making Everyone Safer.
A state-commissioned study found wildlife-vehicle collisions fell sharply along a stretch of I-25 in Colorado after the Colorado Department of Transportation added underpasses, fencing and a large wildlife overpass.
A report commissioned by the Colorado Department of Transportation (CDOT) found that wildlife-vehicle collisions dropped by 91% in the last year studied on a stretch of Interstate 25 on the Douglas and El Paso county border. The decline came after CDOT built most of its planned wildlife mitigation system.
The measures were part of the five-year South Gap project, which began in 2018 to widen the road and improve safety. The system includes five underpasses and 14 miles of fencing on each side of the interstate. Before it was built, wildlife collisions were the third most common crash type on that section, even though they were under-reported, with an average of 32 crashes per year.
The study used crash data and camera monitoring from 2022 to 2024. It showed wildlife-vehicle collisions down about 85% per year on average. Overall crashes declined by 20%, which the report said was likely influenced by roadway changes as well as the wildlife measures.
The final and most visible piece, the Greenland Wildlife Overpass, was completed in December 2025. CDOT says it is the largest of its kind in North America. The $15 million structure measures 200 by 200 feet, has grass growing on it to simulate open grassland, and has a small brush berm to help smaller animals cross without being exposed to predators. It was funded through the Federal Highway Administration's Wildlife Crossings Pilot Program.
Data on the overpass is still being collected, but four CDOT cameras have recorded bears, elk and pronghorn. Julia Kintsch, principal investigator on a study of the overpass, said the elk and pronghorn appearances were a good sign. "That is a really promising sign," she said. Elk and pronghorn tend to avoid underpasses, and CDOT hopes the open design will connect herds on both sides of the highway.
Kintsch's team is collecting genetic data from elk herds on each side to set a baseline. Researchers plan to compare it in five or 10 years to see whether genetic diversity has increased. The first study results are expected in spring 2027. According to the California Department of Transportation, the Wallis Annenberg Wildlife Crossing on U.S. 101 is set to surpass the Greenland overpass in size when it opens this winter.
Note: The headline calls the overpass the largest in North America. The page attributes that to CDOT and says a California crossing, the Wallis Annenberg Wildlife Crossing, is set to surpass it when it opens this winter.
At a Glance
- CDOT's report found a 91% drop in wildlife-vehicle collisions in the last study year, and about 85% per year on average.
- Before the project, wildlife was involved in an average of 32 crashes per year on the I-25 section.
- The Greenland Wildlife Overpass cost $15 million, measures 200 by 200 feet, and was completed in December 2025.
- The system includes five underpasses and 14 miles of fencing along each side of I-25.
- First results of the overpass study are expected in spring 2027.
Sources
This brief was written by Brightside Report from the reporting linked above. Spot an error? Request a correction.