The Colorado Department of Transportation and the Colorado Parks and Wildlife (CPW) agencies recently completed wildlife underpasses along a rural stretch of Interstate 25 between Colorado’s two largest cities, Denver and Colorado Springs.

[Above photo by the Colorado DOT]

This wildlife mitigation system is part of a $419 million transportation improvement project – known as the I-25 South Gap project – that aims to improve safety and travel on 18 miles of I-25 south of the Denver metropolitan region; a route that more than 87,000 motorists use on a daily basis.

The I-25 South Gap project’s wildlife mitigation system includes four new and one refurbished wildlife underpasses, 28 miles of deer fencing, and deer guards and jump-outs, Colorado DOT said.

Work on the underpasses is substantially complete with 8 percent of deer fencing installed – just in time to shepherd migrating wildlife safely under the interstate this fall. The I-25 South Gap project as a whole, however, should be finished by 2022, the agency noted.

The Colorado DOT and CPW are also now in the process of installing 59 cameras throughout the project’s wildlife mitigation system to help measure success.

Shoshana Lew, executive director of the Colorado DOT, said that these wildlife underpasses – used by bears, elk, and small game animals – are also some of the largest in North America.

“One of [our] core values is safety, and we are thrilled to deliver on this value to all who use I-25 in the area,” she explained in a statement.

“In Colorado, nearly 4,000 animal-vehicle crashes are reported annually, resulting in injuries and fatalities to people and costing an estimated $80 million,” Lew added. “In the I-25 South Gap, it is estimated that one animal-vehicle crash occurs per day. Our wildlife mitigation system aims to reduce these crashes by 90 percent.”

“Colorado DOT met with various agencies, including CPW, early in the planning process to come up with a collaborative solution,” noted Brandon Marette, land use coordinator for CPW’s Northeast Region. “Fast forward from our first collaboration meeting nearly five years ago to today, where wildlife is now using the underpasses that we planned together. There is more collaboration to come between our agencies as we continue to plan and implement strategies to keep both people and wildlife species safe, thus protecting what is unique to Colorado.”

State departments of transportation in various parts of the country have been working on ways to improve wildlife mitigation tactics over the past several years.

In 2019, the Pew Trusts issued a report that highlighted the work states are doing to boost safe passage for wildlife around roadways, while at the same time improving motorist safety.

“Big-game animals in the American West today are increasingly squeezed by growing suburban areas, energy development, climate change, and an expanding road network,” noted Matt Skroch, a manager with the Pew Charitable Trusts’ U.S. public lands and rivers conservation team and author of the report, at the time.

“[Those] factors are threatening the landscape connections that wildlife needs to move to and from their seasonal feeding and breeding grounds,” he added. “To conserve wildlife corridors while reducing wildlife-vehicle collisions in the West, state and local governments need to take the lead on these issues and guide their agencies to effectively link science with policy. Fortunately, this is beginning to happen. From Montana to New Mexico, states are identifying hot spots where collisions occur and linking those areas with the larger habitat conservation needs on either side of the road.”

For example, in April, the construction of the new Rock Creek Bridge to replace a culvert on US-20 recently won an engineering excellence award from the American Civil Engineers Council of Idaho – an award shared by the Idaho Transportation Department (ITD) and Jacobs Engineering. That new bridge now allows wildlife to pass under the highway, reducing the risk of possible collisions involving wildlife and vehicles on the roadway.

The ITD added in a statement that this particular section of US-20 witnessed 64 vehicle-wildlife collisions over the last five years, which totals a “societal cost” of approximately $2 million when adding together the cost of vehicle repair or replacement, medical bills, and increased insurance rates – not to mention the cost to wildlife.

If culverts under a busy state road are clogging a creek and preventing fish from migrating, how do you simultaneously replace the culverts, maintain traffic on the road, and protect the fish during construction?

[Above photo by WSDOT]

This riddle proved a real-life challenge for the Washington State Department of Transportation, which came up with an innovative answer – leave the culverts in place, build a new bridge somewhere else, and move the creek under it.

More than 50 years ago, the agency installed two 8-foot box culverts on State Route 3 over Chico Creek, home to the biggest chum salmon population in Kitsap County. In 2013, a federal court ruled that the abutting culverts were among 1,002 fish barriers in western Washington and ordered their removal by 2030.

The reason is that culverts create a “choke point” for fish – accumulating debris, narrowing the creek, and preventing thousands of salmon from making the annual spawning trek through the creek to the freshwater bay to lay their eggs. Above the creek, about 50,000 vehicles a day drive on SR 3, so a construction plan had to consider travel patterns of fish and motorists.

The WSDOT solution is a $58.3 million design-build project that features new bridges on SR 3 and nearby Chico Way, two realigned ramps, and two engineered creeks beneath the new bridges. The project will keep traffic and fish moving during and after construction.

Crews building a new SR 3 bridge just east of the culverts are simultaneously maintaining traffic volumes by shifting lanes toward the outside shoulders while the center portion of the bridge is constructed. Then traffic will shift again, to the inside shoulders, while the rest of the bridge is finished. Once SR 3 bridge construction is completed, crews will realign traffic lanes with the new bridge.

Meanwhile, crews are building an “engineered creek” that will realign Chico Creek to bypass the old culverts to pass under the new bridge. Construction work to redirect Chico Creek to the new channel will take place during “fish windows,” when construction work will do minimal damage to fish.

The engineered creek includes native vegetation, strategic bends, and elevation changes designed to support “every life cycle of fish,” said Doug Adamson, a WSDOT spokesman. It will feature places for fish to lay eggs and hide from predators, allowing the salmon to “naturally move” from fresh water to saltwater habitats and back again, Adamson said.

The project also includes a new bridge, two realigned ramps, and a second engineered creek at nearby Chico Way. This work will eliminate fish barriers to an unnamed tributary that feeds into Chico Creek by realigning the tributary and giving it a much wider channel under the new Chico Way Bridge.

The entire project, which will improve access to 21 miles of potential habitat, is regarded as one of the most significant fish barrier removal projects in western Washington due to the number of fish involved and because of the cultural impact to the Suquamish Tribe, whose ancestors have inhabited the area for thousands of years.

The project comes 30 years after WSDOT first created a dedicated program to remove barriers to fish under state highways. Since 1991, the agency has fixed 344 barriers, opening a total of 1,161 miles of fish habitat. “We are opening up dozens and dozens of miles for habitat for fish who couldn’t reach these areas since the highways were first built,” Adamson said. “We are making up for mistakes made in the past. We are working to rectify those mistakes to improve the habitat for native fish.”