Skip to contents
Environment

Colorado’s I-25 project on “The Gap” combined data, thousands of photos and engineering to minimize roadkill

On vast, contiguous public and private land, abundant wildlife has been meticulously preserved. But growing safety hazards couldn’t be ignored.

A deer lies on the side of Interstate 25 in an area known as The Gap, a stretch between Castle Rock and Monument where the highway shrinks to two lanes in each direction. I-25 runs through this wildlife-rich section of Douglas County, prompting planners on its widening project to devise underpasses that aim to give animals safe passage and reduce wildlife-vehicle collisions. (Provided by Brandon Marette, Colorado Parks and Wildlife)
  • Credibility:

It’s a picturesque and remarkable feat of preservation. Meandering plains, mountains and meadows reflect a decades-long effort to link massive, contiguous public and private parcels along a miles-wide corridor that runs roughly from Monument Hill north to Lone Tree. It features land wrapped in expansive conservation easements, protected habitat and, to the west, Pike National Forest. 

It also teems with wildlife. There’s a herd of elk on billionaire John Malone’s Harmony Ranch that can range from 350-500 animals. Pronghorn, mule and whitetail deer, dozens of bighorn sheep as well as bears and mountain lions range across the varied terrain, as do smaller animals such as coyotes, badgers and wild turkeys.

Countless Front Range motorists may not dwell on these details, but they’re more than a little familiar with the landscape: Their vehicles slice through it every time they buzz down that busy stretch of Interstate 25. 

And that’s been a problem — both for drivers surprised by literal deer in the headlights and the wildlife that for decades has risked becoming roadkill to traverse a four-lane highway through its habitat. With the Colorado Department of Transportation’s current project to widen an 18-mile stretch from Castle Rock to Monument known as The Gap, expanding it to six lanes to accommodate mounting traffic, motorists and wildlife would have made for an even more dangerous and potentially deadly mix.

That’s where about $20 million of the $350 million project comes into play. After extensive data collection and crunching — everything from crash numbers to images from more than a dozen motion-activated cameras — wildlife biologists and engineers have responded to the migration habits of the area’s many species with a mitigation plan designed to drastically reduce the dangerous intersection of vehicles and wildlife.

“The I-25 corridor runs right through the middle of some of our best habitat,” says Andy Hough, environmental resources coordinator for Douglas County Open Space and Natural Resources. “Wildlife have had the ability to cross over the highway, especially at night when traffic volumes are a little bit lower, forever.”

But the ongoing construction to widen, grade and iron out some dangerous curves, scheduled to be completed in 2022, will make I-25 very difficult to cross safely. That means the wildlife Douglas County and its many partners, including private landowners, have spent millions to protect needs some help finding their way to the other side.

“It’s becoming a huge, wide swath of asphalt that will be difficult to cross,” Hough says. “So part of the process was to put up wildlife exclusionary fencing and just keep wildlife off the highway, so they can’t get onto it and, not be able to cross, and then go back and forth like a pinball machine until they’re hit by a vehicle.”

A bear roams through a meadow while vehicles cruise past on Interstate 25 in August of 2017. The image was captured by a motion-sensing camera deployed to determine wildlife patterns along this stretch of highway in Douglas County. (Provided by Colorado Parks and Wildlife)

The project has been about much more than just fencing. In all, CDOT, several partner agencies and contractor Kraemer North America pooled brainpower and procured funding to create five wildlife underpasses and dozens of escape routes for wayward animals, with a much more expensive wildlife overpass on its wish list.

Hough, who helped implement the county’s master plan for wildlife conservation, stresses the significance of this stretch of real estate as Douglas County — and much of the Front Range — continues to develop rapidly. Every new driveway, every new fence, every new resident’s pets combine with the burgeoning traffic at all hours to create potential disturbances to wildlife habitat.

That’s why he speaks of this land with something approaching reverence.

“It has the most contiguous blocks of protected habitat on both sides — the most potential for connectivity,” Hough says. “Everything else is built up or fragmented. We have many square miles of protected high-value habitat, the largest continuous block between Pueblo and Fort Collins. 

“That’s why this corridor is so important.” 

Environmental planning for ways to improve the 34 miles of highway from Lone Tree to Monument began in 2016, and public meetings opened up in January 2017.

Chuck Attardo, I-25 south corridor environmental manager for CDOT, recalls a rush of media attention at those meetings as it quickly became obvious that serious problems needed to be addressed. The Gap denotes the stretch between Denver and Colorado Springs where the thoroughfare shrunk to just two lanes in each direction.

“So you have this big bottleneck,” Attardo explains. “Not only that, you don’t have any shoulders, and these curves are unsafe. Not only that, but the weather can be terrible. So all these things compounded the safety and traffic problems that we heard from the public agencies.

“The other conclusion we came to,” he adds, ”was that the wildlife is part of that problem. Animal-vehicle collisions substantially contribute to the safety and the traffic problem in the 18-mile gap. So that’s kind of how the whole thing started.”

(Provided by Colorado Division of Wildlife)

Attardo assembled what he calls the “bio team,” made up of workers from CDOT, federal and local governments, regulatory agencies and “all kinds of biologists and planners.” They started examining crash data from CDOT, Colorado Parks and Wildlife and Colorado State Patrol records and cross-referencing it to determine the scope and specific locations of the problem. They found plenty, especially in the months of November and June — high migration periods when more than one deer or elk is struck each day, on average.

“So the conclusion we come to is that wildlife mitigation systems need to be part of any project as it goes to construction,” Attardo says. 

But they couldn’t do that without more data. Colorado Parks and Wildlife tracks deer and elk with electronic collars in some regions, but not in this area. So the only data available was CDOT’s maintenance data (basically, what roadkill it cleaned off the pavement) and CSP’s crash data. Further complicating the matter is the fact that many vehicle-wildlife crashes aren’t logged that way. Authorities sometimes log them as speed-related, though CDOT says it’s encouraging the CSP to log them as both.

“Right away,” says Brandon Marette, Northeast Region energy liaison and land use coordinator, “we figured out that there was a data gap.”

He did find out that CPW’s district wildlife managers track bear and mountain lion mortality across the state, though that information was buried in three-ring binders that Marette had to digitize and cross-reference with locations on that stretch of the highway.

But even roadkill data is spotty, Marette notes. Working on the wildlife issues associated with a project on state Colorado 9 near Silverthorne, he learned that roadkills can be underreported by as much as 80%. So he and colleague Karen Voltura, a fellow CPW land-use specialist, set out to supplement the early data. For starters, they knew that I-25 and Tomah Road, near Larkspur, has been a hotspot for wildlife-vehicle collisions.

Dating back to October 2018, CDOT compiled collision data from a 14-mile span within The Gap and came up with these two-year totals: 126 incidents involving 76 deer, 15 bears, 10 mountain lions, four hawks and an owl, plus crashes with about seven other species.

“That’s a pretty high ratio,”Marette says. “With 126 road kills, that tells me this is a very important project for wildlife and motorists. The last thing you want is someone to get in a significant car accident.” 

Overall, The Gap corridor averages a few crashes a day, with about 10% caused by wildlife, according to CDOT, which also adds that the number is probably underreported.

“Many people in both local government and the general public questioned why we’d spend money on this,” Attardo says. “For the people who were skeptical, we had to phrase this in safety terms. It will pay for itself in 15 years. A lot of people are injured from these crashes. By the end of the environmental assessment, almost everybody supported it.”

The next step: cameras.

One of the motion-sensing cameras used to determine where to put wildlife crossings captured this deer, with oncoming headlights along Interstate 25 in the area dubbed The Gap. (Provided by Colorado Parks and Wildlife)

The team chose 12 initial locations between Monument and Larkspur to collect data with motion-sensing still cameras to learn more about wildlife habits along the corridor. Eventually, they’d move the cameras to about 20 other locations to get a complete picture of wildlife use of this stretch of highway. 

What they found out, after workers combed through thousands of photos, was that animals have been moving parallel to and approaching I-25 most places along this 12- to 14-mile stretch — not just a couple common locations. That made their job of locating the underpasses more challenging.  

A CDOT contractor helped Marette with the camera setup and he checked them regularly. One problem with cameras triggered by motion was that anything that moved — even blowing shrubs or tall grasses — produced sometimes worthless images by the thousands 

“One (camera) had thousands of pictures of cows. You have to sort through all those pictures, identify what the species are and whether they’re using existing culverts. Predators were using them, but prey species are not typically using them.”

The cameras also revealed 17 separate species lurking near the highway, not counting cattle,  people and pets that triggered the shutters. Mapping overlays with crash data revealed two hot spots: one near Palmer Divide Road on Monument Hill, dropping into the town of Monument; and the other near that familiar Tomah Road exit, approaching Larkspur.

Wildlife may have been motivated by forage opportunities or seasonal events, such as giving birth. But why they crossed the road wasn’t the issue. 

“Regardless of the why, the important thing to CDOT, CPW and Douglas County is how they’re crossing the road,” Marette says. “Now, if they’re crossing overland when traffic is going 70-80 mph, they don’t stand a chance. By providing five crossing structures, we’re expecting a 90% decline in wildlife (accident) numbers.”

That’s roughly the decrease in wildlife-vehicle accidents in the Colorado 9 project in Summit County. While there’s no guarantee of similar results along I-25, a three-year study once the project has been completed will test that estimate with hard data.

Armed with the information about wildlife tendencies, the bio team sat down with engineers to see what, given the project’s budget, could be done to mitigate the danger. Overpasses are optimal, as their wide-open construction tends to invite many species to make the crossing. But they’re also expensive.

More budget-friendly underpasses seemed to hold the most viable solution. 

“We know our budget is about $350 million, and we know we can’t take any right of way as part of the project, we can’t encroach into that property adjacent to the interstate,” he says. “That’s because we don’t have money or enough time to go through an acquisition process and acquire that property. We had to match up camera data of the important crossings with areas the engineers tell us they have room to squeeze in an underpass.”

The lone exception: the revamped Greenland interchange, which was going to be elevated anyway, making an underpass a safe bet.

This predator prowling along Interstate 25 won’t hesitate to use a culvert for passage across the highway. But prey animals like deer and elk often won’t use culverts because they don’t afford a view to the other side that assures no predators like this one are lying in wait. (Provided by Colorado Parks and Wildlife)

All five of the underpasses were built larger than usual. Size matters, particularly to deer and elk, which are constantly on guard against predators. Though this stretch of I-25 contains some culverts, maybe 5 feet high and 3 feet wide, the field of vision through to the other side isn’t sufficient to allay deer’s suspicions that a predator could be lurking. The photo data indicated that even one large culvert that measured roughly 7×10 feet made them skittish.

“At first glance, it looks like it’s wide enough for deer to go in, and we had many pictures of deer looking in, but deer didn’t go into it,” Marette says. “While it may have been wide enough, it had a dogleg in the middle and they couldn’t see through to the other side. It was a dark tunnel and deer didn’t like that.”

The underpasses being built now are 100 feet wide and 18 feet tall, to provide an unobstructed view of what awaits beyond the highway. 

“It’s a big light at the end of the tunnel, if you will,” Marette says. “That’s a good analogy for the whole project — light at the end of the tunnel for wildlife and motorist safety. Having that wide visual reassurance for deer and elk to go under without fear of a predator on the other end is very important. 

“That said,” he adds, “elk are sort of the problem child, leery of underpasses. That’s why we try to maximize to the tallest and widest extent possible to see if elk will use it. That’s also one aspect of our post-construction study.”

The underpasses also feature familiar flora, with about 6,000 plants going in — about 15 variations of native trees and shrubs to give wildlife even greater confidence in the passage. Sixty-three escape ramps will be available for animals that somehow find their way into the I-25 right of way so they can jump down to safe, familiar habitat. Along with 145,000 linear feet — more than 27 miles — of fencing, the project will feature 22 grates, similar to cattle guards, that discourage animals entering off-limits areas that can’t be fenced.

Although much of the fencing has been erected, there are still opportunities during the construction phases for wildlife to try to sneak across the highway the old way.

“We asked those folks who work for CDOT to keep tabs on animal-vehicle collisions,” Attardo says. “We’re seeing that they’re down a bit. I don’t know if construction interrupted movement of elk and deer in the area.

“But we can see evidence of those areas already being used.” 


The Colorado Sun has no paywall, meaning readers do not have to pay to access stories. We believe vital information needs to be seen by the people impacted, whether it’s a public health crisis, investigative reporting or keeping lawmakers accountable.

This reporting depends on support from readers like you. For just $5/month, you can invest in an informed community.