Frequently Asked Questions

Wildlife crossings are a proven strategy for reducing wildlife-vehicle collisions while also allowing animals to safely access the habitat and resources on either side of a road. Wildlife crossings physically separate wildlife movements from traffic by providing safe passages either under or over a road. Tall fencing directs animals to these passages while preventing them from getting onto the road. 

Wildlife crossings are very effective!

• On Highway 9 in Grand County:

  • A system of 5 underpasses and 2 overpasses along 10-miles of fenced highway reduced collisions by 92% and were used by 17 species of large and medium-sized mammals.

• On Interstate 25 in Douglas County: 

  • 5 large bridge underpasses and 14 miles of fencing reduced wildlife-vehicle collisions by 85% in the first two years post-construction. 

  • The crossings provide passage for mule deer, elk and many other wildlife, including small mammals, amphibians, and reptiles. 

  • The recently constructed Greenland Overpass completes the mitigation system and is expected to allow even more wildlife to cross the interstate to access vast open space lands on either side while further reducing collisions. 

These are just a few examples in Colorado. Across western states and around the nation and the globe, wildlife crossings are being used to reconnect landscapes, support long-distance migrations, and facilitate wildlife movements across landscapes that have been fragmented by roads, development, and other infrastructure. 

Wildlife crossings are highly effective when combined with proper fencing. Studies show:

• Colorado's Highway 9 project reduced crashes by 92% 

• Canada's Banff National Park crossings led to an 80% reduction in wildlife-vehicle incidents, with common species such as deer and elk reduced by 96%

• Wyoming's Trapper's Point project reduced wildlife-vehicle collisions by 80% in the first three years

• Montana's Highway 93 crossings reduced collisions with wildlife by over 70%

The key to effectiveness is combining overpasses and underpasses with fencing systems that guide animals toward safe crossing points rather than onto the highway.

Fencing is essential to the success of wildlife crossings:

• Guides animals: Directs wildlife away from dangerous highway sections toward safe crossing structures

• Prevents access: Keeps animals off the roadway between crossing points

• Maximizes effectiveness: Crossings combined with fencing reduce collisions by 87-97%, versus lower effectiveness without fencing

• Multiple components: Complete systems include:

  • Wildlife fencing along roadways (typically 8 feet tall)

  • Escape ramps for animals that exploit a gap and get trapped on the wrong side of a fence

  • Wildlife guards at access points (driveways and road intersections)

Examples:

• Colorado Highway 9: 10.3 miles of fenced highway  with 29 wildlife guards and 61 escape ramps

• I-25 Gap project: 14 miles of fenced highway with 5 large wildlife underpasses, 1 overpass, 63 escape ramps and abundant wildlife guards. 

• Wyoming's Trapper's Point: 12 miles of fenced highway with 6 wildlife culverts/underpasses

Location selection involves multiple scientific factors:

• Wildlife movement data: GPS collar data, trail cameras, aerial reconnaissance, and migration pattern studies

• Collision history: Areas with high rates of documented wildlife-vehicle collisions

• Habitat connectivity: Locations that connect high-quality habitats on both sides of the highway

• Road characteristics: Areas with high traffic volume, high speeds, and road design challenges

• Landscape features: Natural drainages  and habitat corridors where animals already cross

• Protected land: Areas with surrounding open space or conservation land to maximize long-term benefits

• Development pressure: Locations where opportunities to reconnect habitat still exist (before development closes them)

The Western Slope Wildlife Prioritization Study (WSWPS) is a valuable tool, but it does not tell the whole story of the Roaring Fork Valley’s need—and the agencies that produced it have said as much.

The study evaluated highway segments across two broad categories: safety and crash patterns (approximately half the weighting) and wildlife movement, collision risk, and population-level mortality impacts (approximately half the weighting). Both categories are legitimate and important, and the study was built on the best available data at the time of its completion.

The primary reason the Roaring Fork Valley did not rank higher is not a reflection of low actual risk: wildlife-vehicle collision data from this corridor has historically been under-reported in the statewide crash database. Pitkin County Sheriff’s Office is now submitting WVC crash reports directly to the state to ensure future analyses reflect the true scope of the issue here. It is also worth noting that no prioritization study can place every high-need segment in its top tier—by definition, not every segment can rank in the 95th percentile. The study was designed to guide statewide agency-led efforts, not to serve as the sole determinant of which communities could or should act.

The Highway 82/133 study conducted by Roaring Fork Safe Passages in partnership with local agencies provides a valid, actionable, and locally-grounded analysis of the valley’s specific needs. It is consistent with the data that does exist in state databases and is supported by extensive GPS collar data, trail camera documentation, and a decade of local collision records.

CDOT and CPW have demonstrated a clear willingness to partner on projects that fall below the 95th percentile threshold when local need, partnership strength, and community support are compelling. The I-70 East Vail Pass project is a prominent example: it ranks in the 62nd percentile on the statewide prioritization study—well below the top tier—yet it is one of the Colorado Wildlife and Transportation Alliance’s six highest-priority funding targets, because it demonstrates documented connectivity need, broad partnerships, and strong community backing. The Roaring Fork Valley presents an equally compelling case.

Across Colorado, local communities are stepping up to address wildlife connectivity and WVC reduction. This is not a workaround—it is how many of the state’s most successful crossing projects have come to exist. CDOT and CPW have explicitly recognized that the need for crossings extends beyond what agencies can address independently, and that community-led partnerships allow far more projects to move forward than would otherwise be possible. Our locally-driven effort is a model of this approach, not an outlier to it.

The timeline varies significantly depending on project complexity:

• Planning and design phase: Can take at least 2-5 years to identify locations, secure funding, complete environmental studies, and finalize engineering designs

• Construction phase: Typically 1-2 years once funding is secured 

• Notable example: Colorado's I-25 Greenland overpass was completed in less than a year, ahead of schedule—though this is considered exceptionally fast for large infrastructure projects

• Total timeline: From initial concept to completion, most projects take 3-10 years, however some take 20 years to realize

It's important to note that identifying the best locations and securing funding often takes longer than the actual construction.

Several factors make immediate action critical:

• Development pressure: As the valley continues to develop, wildlife corridors are at risk of being severed, making wildlife populations less resilient.

• Traffic growth: Traffic on Highway 82 is projected to reach 26,400 vehicles per day by 2045, making the problem worse and creating a major barrier to wildlife movements.

• Limited opportunities: Land protection and corridor preservation opportunities won't be available indefinitely—once development closes these corridors, they're lost forever

• Declining elk & deer populations: Elk and deer populations are already declining in Pitkin and Eagle Counties due to a multitude of impacts from development, roads, and recreation, with elk calf recruitment below objective in both local herds

• Increased moose populations: Colorado’s moose population has grown by more than 50% over the past two decades with moose crashes being about ~18x more likely to be fatal than deer crashes. 

• Strategic investment: Building now prevents worse problems and higher costs later