As drivers eagerly await the lane expansion in the “Gap” on Interstate 25, so, too, might local and migrating wildlife searching for a safe crossing amid high-speed traffic.
“As we create barriers to wildlife movement like roads, wildlife are more likely to get stuck or hit,” said Chuck Attardo, the I-25 South Program’s environmental manager. “What’s been going on in the past 30 to 40 years is that people are trying to figure out a way to create permeability in these barriers, and the best way is to create underpasses, dig a tunnel or create an overpass.”
Between 2005 and 2017, 785 animals were killed on I-25 between mile markers 160 and 180, according to data provided by CDOT. These crashes have amounted to more than $4 million in human injury and more than $3 million in property damage costs.
“The numbers were alarming enough to CDOT engineers that they mentioned them in a safety assessment report that we compiled for I-25 about a year and a half ago,” Attardo said. “In May-June and October-November, about one to two animals were hit a day.”
On I-25, new underpasses will be built just north and south of County Line Road and near mile markers 167 and 172. The culvert just north of the bend in the road at mile marker 172 will be doubled in size.
Each will cost about $6 million of the $350 million project budget and will be constructed during Phase II and III, though no official date has been set, Attardo said.
The pathways are designed with large mammals in mind in terms of size and shape. Prey species — mule deer and elk — search for a route of travel with a clear line of sight to protect themselves from a lurking predator, said Karen Voltura, Colorado Parks and Wildlife Southeast Region’s energy liaison and land-use specialist.
“Prey species are hypervigilant,” she said. “They won’t go into a blind, dark tunnel with turns they can’t see beyond. They want to see daylight and attractive habitat on the other side.”
Underpass design is only one way of encouraging wildlife to use the crossings. CDOT will also install 8-foot-tall fencing to funnel animals toward the openings.
Projects like this are scattered across Colorado.
CDOT points to the two overpasses and five underpasses constructed on 11 miles of Colorado 9 between Kremmling and Steamboat Springs, finished in December 2016, as a model for success. In a study published in March, CDOT found that the number of mule deer and elk carcasses found on the highway decreased by 86 percent from a five-year average of 56.4 to a total of eight between the completion of construction and April 2017.
The study also found that wildlife used the seven crossings 83 to 99 percent of the time.
Wildlife-vehicle collisions reported to law enforcement decreased by 70 percent to three crashes between 2015 and 2016, before three of the crossings constructed during the second phase of the project were finished.
Funding was recently secured for a project on I-70 on Vail Pass. There, the area surrounding the pass is “largely an intact landscape,” said Paige Singer of Rocky Mountain Wild, an advocate for wildlife crossings and landscape connectivity.
“Increasing connectivity up there is a no-brainer,” she said. “In our four years of monitoring up there, we’ve seen bear, mountain lion, the only known breeding population of Canada lynx outside southwest Colorado, mule deer and elk. Those crossings will help a lot of species up there.”
Officials hope five culverts slated for I-25 won’t be the last of the constructed wildlife crossings. Voltura and Attardo hope for an overpass and the expansion of more culverts.
“We acknowledge that (what is in the plan) is minimal,” Voltura said. “So when we come back to long-term planning, we can think of possibilities like an overpass, or if we are replacing a culvert, can we size it up?”
“Little things like that make a difference,” she said.
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