Our Approach
Restoring ecological connectivity between the north and south Cascades though wildlife bridges, underpasses and habitat restoration along I-90.
For more than a century, I-90 has split the Cascades in half, isolating wildlife and disrupting ecological processes. Through long standing collaboration with WSDOT, Tribes, conservation partners, and local communities, we helped secure and shape the Snoqualmie Pass East Project, which now includes Washington’s first wildlife overpass and multiple large undercrossings. We continue to restore habitat, improve older crossings, and monitor wildlife use so species can move safely between the north and south Cascades.
Current Focus
Work We’re Doing to Achieve Interstate 90 - Central Cascades Goals
Wildlife Crossings
We helped catalyze one of the most significant wildlife crossing projects in the country by advocating for the inclusion of wildlife bridges, large underpasses, and improved culverts in WSDOT’s I-90 Snoqualmie Pass East Project.
Working alongside the U.S. Forest Service, Forterra, Sierra Club, The Nature Conservancy, Mountains to Sound Greenway Trust, American Rivers, The Summit at Snoqualmie, and many other partners, we pushed for infrastructure that reconnects habitat across the Cascade Crest while improving driver safety.
These crossings now serve as a national model for how transportation and conservation goals can align to restore ecological function across major highways.
Crossing Improvements
We also work to improve historic wildlife crossings along I-90, including Washington’s oldest undercrossing near Milepost 27.
In partnership with WSDOT, WDFW, the Rocky Mountain Elk Foundation, and the Ruffed Grouse Society, we removed an acre of blackberry and widened fencing to improve visual security for elk and other species moving through this high-conflict area. This combination of advocacy, restoration, and long-term partnership ensures that I-90 continues to evolve into a safer, more connected landscape for wildlife and people.
Our ongoing role is to support monitoring, maintenance, and future improvements that keep this critical corridor functioning as a lifeline across the Cascades.
Impact & Results
A History of Interstate 90 - Central Cascades
For more than two decades, partners have worked to reconnect habitat across I-90 at Snoqualmie Pass. Through sustained advocacy, infrastructure investment, and scientific monitoring, the corridor has become a leading example of wildlife connectivity and transportation planning in North America.
Advancing safe passage through long term partnerships and advocacy
Ongoing construction to expand connectivity across the Cascades
Documented success through scientific monitoring
Advancing safe passage through long term partnerships and advocacy
Through the historic I-90 Wildlife Corridor Campaign and the I-90 Wildlife Bridges Coalition, Conservation Northwest has worked with WSDOT, elected officials, and community partners to make the Snoqualmie Pass corridor safer for wildlife and people. Phases 1 and 2 of the Snoqualmie Pass East Project are complete, including Washington’s first wildlife overcrossing built in 2018.
Ongoing construction to expand connectivity across the Cascades
Phase 3 of the project is now underway, widening the highway, straightening curves, and replacing bridges and culverts. By 2031, this 15 mile, $1 billion phase will add 16 additional wildlife crossings, significantly expanding safe movement opportunities across the Cascade Crest.
Documented success through scientific monitoring
Central Washington University researchers have recorded more than 5,000 animals using the I-90 wildlife crossings each year. These numbers do not include many small mammals and low mobility species—such as northern flying squirrels, Pacific tree frogs, banana slugs, and coastal giant salamanders—that often go undetected by cameras, indicating the true usage is even higher.
Impact & Results
Our Key Accomplishments for Interstate 90 - Central Cascades
From protecting critical landscapes to advancing collaborative forest restoration, these efforts deliver lasting benefits for wildlife, habitat connectivity, and climate resilience.
Wildlife Bridge
Helping Build Washington’s First Dedicated Wildlife Overcrossing
In 2018, the program helped secure the political, social, and funding support needed to build Washington’s first dedicated wildlife bridge, reconnecting core habitat across the Cascade Crest at Snoqualmie Pass.
Habitat Restoration
Revegetating Crossing Structures to Improve Wildlife Movement
Since 2015, the program has supported revegetation around I-90 crossing structures, planting more than 80,000 native plants to create natural cover and improve wildlife use of the overpass and underpasses.
Undercrossing Improvements
Enhancing the Milepost 27 Crossing for Safer Wildlife Passage
The program has improved the historic Milepost 27 undercrossing, organizing volunteer work parties to clear blackberry and dense brush, restoring the open sight lines needed for elk and other species to safely move through.
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