As part of an ambitious effort to improve a 15-mile stretch of Interstate 90 (I-90) east of Snoqualmie Pass, Washington, the Washington State Department of Transportation is planning to install more than 20 wildlife underpasses, 3 overpasses, and wildlife fencing. Crossing structures have been designed and located with a broad range of species in mind—from amphibians to wide-ranging mammals. A key component of the I-90 project is its commitment to extensive wildlife monitoring. The long-term and multi-phased nature of this project makes it possible to collect valuable baseline data prior to construction. Ultimately, wildlife monitoring data will help researchers evaluate whether the crossing structures provide an effective means for wildlife to cross I-90. The Western Transportation Institute is currently overseeing the wildlife monitoring program at Snoqualmie Pass East. The flying squirrel project in particular is evaluating the current barrier effects of I-90 on flying squirrels, including if and how often squirrels cross the highway, and to what extent the highway is a barrier to gene flow for this species. Future studies conducted after the construction of crossing structures will evaluate whether the structures have helped increase connectivity for flying squirrels.