I-25 wildlife crossings linked to fewer animal-vehicle collisions
The story at a glance
A Colorado Department of Transportation-funded study reported an 85% average reduction in wildlife-vehicle collisions during the first two post-construction years for a package of measures on I-25. Its reported 91% reduction was in the final study year, before the Greenland wildlife overpass was completed.123
The overpass opened in December 2025 as part of the wider South Gap crossing system. Later reporting described two animal collisions in roughly its first ten months and a 91% fall, but attributed that figure to the system as a whole, not the overpass alone.24
The story in brief
What you need to know
- The formal monitoring study examined five underpasses, wildlife fencing, escape ramps and wildlife guards. It found an 85% average reduction in collisions in the first two post-construction years, with a 91% reduction in its final study year. These figures describe the wider intervention package, not the Greenland overpass.1
- The Greenland overpass was completed after the formal study period. CDOT says it spans six lanes and connects 39,000 acres of habitat, completing a system along the 18-mile South Gap corridor. It was designed in particular for elk and pronghorn.12
- An October 2026 report said two animal collisions were recorded in roughly the first ten months after the overpass opened, describing this as a 91% reduction. That later figure is a separate post-opening account and should not be conflated with the formal study’s earlier result.14
- The formal study’s data came from a period before the overpass was built. Later reporting describes a 91% reduction for the full crossing system after opening, but the sources reviewed do not provide enough detail to reconcile the two figures’ baselines and denominators.1234
- The evidence supports careful reporting of the crossing system’s results, but does not isolate how much the overpass itself contributed. That distinction matters when assessing the performance of individual structures within a wider package of measures.123
Conservation context
Why this matters
For practitioners, the case underlines the value of separating results for an entire crossing system from the effects of one structure. Clear time periods and measures help make monitoring and evaluation useful when judging conservation infrastructure.1234
The developing story
What happens next
Continued monitoring will be needed to assess collision rates over time and whether the crossing system improves wildlife movement and genetic connectivity. The sources say these longer-term effects remain under study.13
Established evidence
What we know
- The formal I-25 South Gap Wildlife Monitoring Study analysed camera and crash data from 2022 to 2024.1
- The study detected 17 species using small-animal cover features that were not detected at the large underpasses. This included two detections of the federally threatened Preble’s meadow jumping mouse.1
- For its collision counts, CDOT draws on reports from state troopers, maintenance staff and drivers, and also tracks carcasses removed by road crews, according to later reporting.4
- CDOT describes the Greenland overpass as completing a wider crossing system on the South Gap corridor, rather than functioning as a standalone project.2
Open questions
What we don't know
- The sources reviewed do not specify the baseline period, corridor length, collision definition and reporting denominator behind the post-opening 91% figure.134
- The overpass’s separate contribution to any reduction in collisions has not been isolated from the underpasses, fencing and other measures.123
- It remains to be established whether the reported changes will persist and lead to longer-term improvements in wildlife movement or genetic connectivity.13
Source coverage
