A long-planned project, designed to reconnect two isolated habitats, is now visible to westbound I-90 travelers.

A large, half-built tunnel covers the interstate near Snoqualmie Pass. The tunnel, when complete, will allow animals to travel unimpeded over Washington’s busiest interstate.

The construction, which is part of the larger billion-dollar project, will connect two important animal habitats.

“You have a really limited bottleneck for wildlife to move from the north to south Cascades,” said Jen Watkins, Conservation Northwest’s I-90 Wildlife Bridges Coalition coordinator.

The overpass is in the Price Creek area near mile marker 62, just east of the summit.

Already there are two animal underpasses on that stretch of interstate. The animal overpass is a rare infrastructure feature in Washington, with only one other similar structure in the state. That structure is located in urban King County.

Overpass construction is slated to finish in fall 2019, said Meagan Lott, a spokeswoman for the Washington State Department of Transportation.

“We did a lot of animal monitoring,” she said. “And this kind of showed that this was a natural migration pattern for animals coming down from the mountain.”

The $6.2 million project is one of 20 planned I-90 animal crossings in Washington on I-90.

Larger animals, like elk, don’t like traveling underground. The overpass is designed to give the easiest and most natural path forward.

While the overpass is being completed, Lott said the underpasses are seeing substantial animal traffic.

“It’s astonishing to see how much wildlife is using the undercrossing,” she said.

Photos of animals using the underpasses are available online.

The underpasses also connect previously bifurcated waterways.

“What makes I-90 so unique … is it’s doing a remarkable job of reconnecting the waterways and the fish habitats,” Watkins said.

The mountainous project area poses its own challenges.

“When you’re dealing with a mountain pass you only get six months out of the year to do what you need to get done,” Lott said. “So there is a unique challenge with that.”

The animal crossings are the result of a partnership between WSDOT, Conservation Northwest and the Forest Service, Watkins said.

Conservation Northwest got involved in the project in 2004, after the conservation organization had finished purchasing about 40,000 acres south and north of I-90. That conservation effort morphed into the animal crossing project. Now, Conservation Northwest administers the I-90 Wildlife Bridges Coalition, which includes the Forest Service, WSDOT, businesses and other partners.

Conservation Northwest’s role is primarily advocating for continued funding of the animal crossings, marketing and explaining the project to the public and running a citizen wildlife monitoring program, Watkins said.

In January, the 30-minute documentary “Cascade Crossroads” was released by the I-90 Wildlife Bridges Coalition in an effort to educate the public, while simultaneously explaining the benefits of the project.

Watkins said the project may serve as a road map for future statewide projects. Because the interstate passes through national forest, like many highways and freeways in Washington, Watkins hopes the model used at Snoqualmie can be replicated.

“That’s a really cool synergy that we could repeat,” Watkins said.

The Washington project was initially modeled after an underpass and overpass in Banff National Park, which crosses over the Trans-Canada Highway.

Since that overpass opened 20 years ago, it’s estimated that 152,000 animals have crossed safely.

Freeways and roads have long disrupted natural animal migration paths, leading to increased mortality and fragmenting habitats.

The I-90 project is the first of its kind in Washington to try and balance human transportation needs with wildlife habitats, Lott said.

“You’re improving safety, you’re relieving congestion and you’re also looking at the environmental aspects,” she said.

Clarification: This story was updated to clarify the groups involved in the I-90 Wildlife Bridges Coalition.