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Colorado wildlife overpass cuts I-25 collisions as habitat reconnects

Colorado wildlife overpass cuts I-25 collisions as habitat reconnects

Built World

North America's largest wildlife crossing cut I-25 collisions 91 percent in its first ten months

October 1st, 2026: Elk connectivity study planned to track the overpass's effect

Overview

Updated Oct 16

Interstate 25 near Colorado's Greenland exit split 39,000 acres of habitat, and for decades elk and pronghorn could not cross it. The corridor averaged about one deer-vehicle crash per day in peak migration. In the overpass's first ten months, wildlife collisions dropped 91 percent, from a five-year average of roughly 40 a year to two.

The 209-by-200-foot bridge works with five underpasses and fencing to guide animals across six lanes of traffic. Researchers are now testing elk droppings from both sides of the highway to see whether the crossing reconnects herds it had split. A state law raises about $3 million a year toward more crossings, but the federal grant program that paid for this one expires unless Congress renews it.

Why it matters

One crossing cut wildlife collisions by 91 percent; if Colorado repeats it, fewer drivers crash and split habitats reconnect.

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Key Indicators

91%
Reduction in wildlife-vehicle collisions
In the overpass's first ten months after it opened in December 2025.
2
Wildlife collisions in the first ten months
Down from a five-year average of roughly 40 a year on the stretch.
5
Wildlife underpasses in the system
Part of the mitigation network completed under the I-25 South Gap project.
$15M
Final construction cost of the overpass
Finished by contractor Kraemer North America at about half the funds allocated.
100,000+
Vehicles crossing this section of I-25 daily
Traffic volume on the corridor the overpass spans.

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People Involved

Chuck Attardo
Chuck Attardo
Environmental Manager, Colorado Department of Transportation
Leading CDOT's wildlife mitigation program
MM
Matt Martinez
Area Wildlife Manager, Colorado Parks and Wildlife
Tracking wildlife use of the crossings
 Shoshana Lew
Shoshana Lew
Executive Director, Colorado Department of Transportation
Oversaw the crossing's completion

Organizations Involved

Colorado Department of Transportation
Colorado Department of Transportation
State agency
Designed, funded, and operates the wildlife mitigation system

State agency that led the South Gap corridor project and built the Greenland overpass.
Colorado Parks and Wildlife
Colorado Parks and Wildlife
State agency
Provided biological expertise and monitors animal use

State wildlife agency that documented elk, deer, and pronghorn using the crossings.
Kraemer North America
Kraemer North America
Construction contractor
Built the overpass under budget

Contractor that completed the 209-by-200-foot overpass for $15 million.
Federal Highway Administration (FHWA)
Federal Highway Administration (FHWA)
Federal agency
Provided the main funding through its Wildlife Crossings Pilot Program

Federal agency that granted $22 million for the overpass.
EC
Environment Colorado
Advocacy group
Running wildlife survey campaigns with Colorado drivers

Advocacy group enlisting Colorado drivers to map wildlife-vehicle collision zones and press for crossing funding.

Timeline

January 2018 October 2026

6 events Latest: October 1st, 2026 · 1 month ago
Tap a bar to jump to that date

  1. Elk connectivity study planned to track the overpass's effect

    Latest Research

    A study comparing DNA from elk droppings on both sides of I-25 will test whether the overpass reconnects herds the highway had separated. Baseline samples were collected before construction.

  2. Drivers recruited to map wildlife collisions as federal grant money runs low

    Funding

    Conservation advocates enlisted Colorado drivers to log where wildlife collisions happen, while the federal Wildlife Crossings Pilot Program that funded the Greenland overpass runs out of money unless reauthorized. New funding likely waits for the next Congress after the midterm election.

  3. Ten-month data shows two collisions on the corridor

    Report

    Coverage of the crossing's first ten months put wildlife collisions on the I-25 stretch at two, down from a five-year average of roughly 40 a year.

  4. Study shows 91 percent collision reduction

    Report

    CDOT research reports a 91 percent drop in wildlife-vehicle collisions on the corridor, with elk and pronghorn crossing for the first time in decades.

  5. Greenland wildlife overpass opens

    Opening

    North America's largest wildlife overpass opens near the Greenland exit, ahead of schedule and under budget.

  6. CDOT starts South Gap widening project

    Construction

    CDOT begins a five-year project to widen 18 miles of I-25 from Castle Rock to Monument, with wildlife mitigation built in.

Scenarios

1

CDOT breaks ground on next Colorado wildlife crossing

Possible Resolves by End of 2027

Discussed by: CDOT officials and the state's new mitigation funding stream

CDOT already keeps a priority list of corridors needing crossings, including Raton Pass on I-25 near the New Mexico border, US-40 near Empire, and State Highway 160 near Mesa Verde. A state law passed this year raises about $3 million annually for wildlife mitigation, which officials say they can use as match for larger federal grants. The open question is when the next project moves from planning to construction.

2

Colorado study confirms elk and pronghorn herds reconnected across I-25

Likely Resolves by Jul 1, 2027

Discussed by: CDOT and Colorado Parks and Wildlife researchers

First results from a study on how animals adapt to the large overpass are expected in spring 2027. Cameras have already recorded elk herds and pronghorn crossing for the first time in decades. The study will show whether the structure genuinely connects herds on the east and west sides of the interstate.

3

I-25 wildlife collisions stay near record low in second year

Likely Resolves by Jan 31, 2027

Discussed by: CDOT crash monitoring

The 91 percent figure came from data spanning 2022 to 2024, after most mitigation measures were built. CDOT continues tracking crashes, cameras, and animal crossings. A sustained reduction would strengthen the case for building similar crossings across the state and the West.

4

Federal crossing grant program expires, stalling Colorado's next overpass

Possible Resolves by Jan 31, 2027

Discussed by: Colorado officials, conservation advocates including Environment Colorado's Henry Stiles

The federal Wildlife Crossings Pilot Program that funded the Greenland overpass expires unless reauthorized, and new money likely waits for the next Congress seated after the midterm election. Colorado's state law raises about $3 million a year, which CDOT says can serve as match for federal grants but not replace them. Without the program, CDOT's priority list of future crossings may sit.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

Mid-1990s onward

Banff wildlife crossings (1996)

Canada's Banff National Park began installing wildlife overpasses and underpasses on the Trans-Canada Highway in 1996, among the first such large-scale crossings in the world. Over the following years, elk and deer deaths on the park's highway stretch dropped sharply as animals learned to use the structures.

Then

Wildlife-vehicle collisions in the monitored area fell by roughly 80 percent.

Now

Banff became the model for wildlife crossings across North America, including the Colorado project.

Why this matters now

Banff demonstrated the approach Colorado is now scaling, from single structures to statewide corridor programs.

1988 to present

Netherlands ecoducts (1988)

The Netherlands built its first ecoduct, a wildlife overpass near Arnhem, in 1988 to reconnect habitat split by roads and railways. The country has since constructed more than 600 wildlife crossings, some spanning hundreds of meters.

Then

The crossings reduced roadkill and let deer, wild boar, and small species move between protected areas.

Now

The Dutch network became the world's densest system of wildlife crossings and a reference for other nations.

Why this matters now

It shows what a mature network of wildlife crossings looks like and gives Colorado a long-term model beyond single projects.

Sources

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The Optimist Daily CBS Colorado The Gazette Colorado Department of Transportation Good News Network Daily Telluridian Axios Douglas County The Slope We are Home