A major highway can function like a wall through an ecosystem.
Animals trying to reach food, mates or seasonal habitat face traffic, while drivers face the danger of collisions. Populations on opposite sides can become increasingly isolated.
Washington's Snoqualmie Pass East project has treated that ecological problem as part of the interstate itself.
Across a 15-mile section of I-90 between Hyak and Easton, the state has combined highway reconstruction with wildlife overpasses, underpasses, culverts and continuous fencing that guides animals toward safer routes.
WSDOT and its partners built 11 large crossing structures in the completed first two phases.
The most important evidence is not that the structures look promising. It is that animals repeatedly use them.
At the end of 2023, motion-activated cameras recorded the 25,000th safe crossing at completed project structures since monitoring began in 2014.
The documented crossings included 7,967 elk, 13,525 deer and 3,216 coyotes. Six cougar crossings had been recorded, five of them during 2023, alongside use by rarer species and smaller animals documented through additional monitoring.
The eventual corridor plan includes more than 20 large wildlife crossing structures. Phase 3 remained under construction in 2026, so the network is still growing.
The progress here is implemented infrastructure producing observable behavior: the crossing structures are reconnecting habitat in a place where a busy interstate had divided it.