Snoqualmie Pass Wildlife Crossing Structures: A Bridge to Safety for Washington Animals Big and Small

Five and a half years ago, I wrote about a new Wildlife Crossing Structure being built east of Snoqualmie Pass near Lake Keechelus.

Animal crossings, also known as ecoducts or wildlife bridges, are quite common in Europe. Countries like the Netherlands, Switzerland, France, Canada and Germany have been using various structures to reduce human-wildlife conflict since the 1950s.

Washington State joined those countries with efforts to allow animals to cross human structures safely, reduce animal-car collisions and habitat fragmentation. This first wildlife overcrossing on I-90 cost approximately 6 million dollars and was part of a $2.4 billion highway improvement project.

Over the years, I’ve kept up with the project by following the I90 Wildlife Watch Facebook page and, from what I saw, considered the project to be a resounding success.

Still, every time the crossings project is brought up on various social media threads, many naysayers complain about the structure’s cost, questioning if these crossings work and doubting the need for their existence.

Since 2000, through The Cascades Conservation Partnership and the I-90 Wildlife Bridges Coalition, Conservation NW has led efforts to reconnect Washington’s north and the south Cascades by protecting and restoring habitat and establishing safe wildlife crossings under and over I-90.

So, I decided to ask Andrea Wolf-Buck, the communications director for Conservation NW, for an update on how the Snoqualmie Pass bridge has helped improve the situation for animals and humans along that stretch of I90.

According to Wolf-Buck, eleven large wildlife crossing structures are currently completed, with a planned total of twenty-six large ones and many smaller ones. The Snoqualmie overpass was technically done in 2018, but fencing wasn’t added until 2019.

The Washington State Department of Transportation (WSDOT) is about halfway through the 15-mile massive, multi-year expansion of I-90 between Hyak and Easton that redesigns and adds two additional lanes to the heavily traveled east-west connector route. 

I asked for statistics on how many animals have crossed the structure since its completion. Wolf Buck said that typically, in other locations, The usually wary elk take up to five years before they begin using new structures on the landscape.

In this case, elk used the overpass and nearby underpasses within months of completion, much faster than expected. She added, “As they adapt to the structure, they will use it more. We saw about twice as many elk overpass crossings in 2021 as 2020, and that will likely continue to increase.”

Structure preference is an ongoing debate, and Snoqualmie Pass East is a living classroom that will provide decades of new information. Since there are big underpasses within a couple of 100 ft of the overpass, they can directly assess species preference. The best news is that the animals don’t have to move far to find a suitable structure because so many varied types are available.

For instance, while not statistically validated, Conservation NW sees a preference for overpasses by coyotes. Early data shows coyotes prefer the overpass nearly 10 to 1 compared to the nearby underpasses.

All the other species seem happy to use either structure type. The only documented cougar crossing in the project area was at an underpass; the same goes for black bears. Deer seem happy with anything; otters like the structures with streams through them, and while the elk love hanging out on the overpass, they also seem happy to cross using the underpasses, often bedding down beneath them.

Wildlife-vehicle collisions in the fenced project area, about the first 7.5 miles, are now non-existent. Considering the average cost of a deer-vehicle collision in Washington is $6,500, wildlife crossings are a worthy investment and less expensive than many other infrastructure projects.

In 2020, across all completed structures, the group detected 4286 wildlife crossings. In 2021, 4400 wildlife crossings. Says, Wolf-Buck, “they are working very well!”

They hope to develop a long-term legislative support package to allow funds to be used on the highest priority highways and corridors to allow species movements. The most recent projects are on Highway 97 and Interstate 5 with Conservation NW’s “Cascades to Olympics” program. The work also continues on the I-5 Cascades to Olympics corridor and will add 11 more miles on HWY 97. Funding has yet to be secured for these locations, but they hope that changes soon.

For more about the story of partnerships between WSDOT, conservation groups, and other state agencies to make improvements to I-90 east of Snoqualmie Pass for both drivers and wildlife, you can watch this YouTube Video.

Thanks for all you do for Washington State’s Wildlife Conservation Northwest!