Earth Protect Blog

I-25 tunnels expected to reduce wildlife-vehicle collisions by 90%

By John Aguilar

The Denver Post

PALMER LAKE » Trying to dodge and weave across six lanes of interstate highway traffic between Colorado’s two largest cities — where 87,000 vehicles a day move through at 75 mph — is not for the faint of heart.

And for the wildlife that attempt to cross Interstate 25 south of Castle Rock, it’s often a lethal outcome.

Nearly 200 animals — including 119 deer, 18 black bears, 10 mountain lions and one moose — have been struck by motorists over the last 4K years on the 18-mile stretch of I-25 between Denver and Colorado Springs known as the Gap, resulting in millions of dollars in propertydamage and personal injury costs.

But a $20 million system to reduce those collisions by as much as 90% is now in place: Five wildlife underpasses buttressed by 28 miles of 8-foot-high wildlife fencing on both sides of the highway will allow safe passage for the animals that migrate through the area on a daily basis in search of food, mates and habitat.

“All kinds of animals — you name it — they’ve been through here,” said Chuck Attardo, I-25 environment manager with the Colorado Department of Transportation. “This is one of the largest contiguous habitats on the Front Range that is still protected.”

Preserving habitat and providing wildlife a way to safely cross Colorado’s thousands of roads and highways, which act as unnatural barriers to animal movement, has become a priority for state officials. Gov. Jared Polis signed an executive order two years ago supporting the protection of wildlife habitat and migratory routes, as well as public safety.

And in late September, the governor heralded the release of the Big Game Migration and Wildlife Connectivity Policy Report, which laid out policy recommendations to better keep animal habitat intact and reduce the nearly 4,000 vehicle-wildlife collisions that occur on average every year in Colorado, causing more than $80 million in property and personal damage.

So when it was time to expand I-25 south of the metro area several years ago, wildlife biologist and land use coordinator Brandon Marette, with Colorado Parks and Wildlife, said it would be the perfect opportunity to “advance the science of wildlife crossings.”

“We needed travel reliability for motorists going between Denver and Colorado Springs and we needed reliability for animals moving between different habitats,” he said. “That was our goal — to make it as accommodating as possible.”

To that end, the underpasses are big — three of them are 18 feet tall and 100 feet wide while another is 300 feet wide — and they’re lined with piled sticks and vegetation to replicate a natural landscape. There are also 67 “escape ramps” for animals that find themselves trapped inside the highway corridor between crossings.

“We wanted to get the field knowledge into the actual design of these structures,” Marette said.

Given its generous size, CDOT claims the network of underpasses in the Gap makes it one of the biggest wildlife mitigation projects in North America.

For elk and deer, prey animals that tend to be “skittish” about entering constricted spaces where their sight lines to predator activity are restricted, the larger and wider underpasses are crucial, he said. Early video surveillance footage has shown elk, deer and a bear already using the tunnels.

“It’s been very encouraging,” Marette said.

Wildlife officials will have a better idea of how many animals are entering the I-25 tunnels in a few years. Just three weeks ago, they started setting up 59 video cameras along the corridor that will capture activity at each crossing.

There are also plans for a massive $20 million wildlife overpass near the Greenland exit, measuring 400 feet long by 200 feet wide, and largely aimed at elk. Groundbreaking on the overpass is tentatively scheduled for 2023.

Lessons on the efficacy of crossings in Colorado can be garnered from a fiveyear study done by CPW and CDOT and released in March on the seven wildlife crossing structures that were installed on Colorado 9 between Kremmling and Green Mountain Reservoir.

“The research documented 112,678 mule deer successful passages across the seven structures, with an overall success rate of 96% and demonstrated the success of the crossing structures in maintaining connectivity for mule deer across the highway for all age and gender classes of the population,” the report stated.

The report estimates a decrease in wildlife-vehicle crashes reported to law enforcement in that stretch of road of 92% and “supplementary carcass counts by 90% relative to pre-construction levels.” That translates into an average of 13 fewer crashes and 56 fewer mule deer deaths each year, according to the report.

“Altogether, the wildlife crossings, continuous fencing, and associated mitigation features achieved major safety benefits … ,” the report said.

Andy Hough, environmental resources coordinator for Douglas County, said there will be plenty of opportunities to test the resilience and effectiveness of the new system in the Gap. With $260 million worth of open space purchases by the county and conservation easements placed on wide swaths of land in the I-25 corridor south of Castle Rock over the past 25 years — and with the Pike-San Isabel National Forest looming off to the west — wildlife is plentiful and active in the area.

Aside from elk, deer and black bear, there are coyotes, pronghorns, mountain lions and bighorn sheep. There are also a lot more people in the area than there ever were.

Data from the 2020 Census revealed that Colorado added nearly 775,000 new residents between 2010 and 2020, with the bulk of that growth happening along the Front Range. And with the Gap expansion project wrapping up next year, that means a new managed lane in each direction on I-25 will be in operation, “effectively cutting off” animal migration routes.

“There are a lot more lanes and a lot more vehicles at more times of day,” Hough said. “To already see elk using these things, I am very pleased.” John Aguilar: 303-954-1695, This email address is being protected from spambots. You need JavaScript enabled to view it. or @abuvthefold