Using an Interstate Highway Expansion Project to Improve Ecosystem Connectivity and Fish Passage in the Pacific Northwest

A major highway project to expand Interstate 90 over Snoqualmie Pass, WA was recently initiated by the Washington State Department of Transportation. The construction project includes wildlife overcrossings, bridges to replace culverts, and the construction of new stream channels to improve fish passage. A diverse group of agencies and private conservation groups have collaborated to ensure that the project will improve ecological connectivity in the Cascade Mountains ecosystem. The collaborative efforts between design engineers, biologists, and conservation groups have resulted in a new roadway that will meet current and future transportation needs as well as allow for ecological connectivity by providing a variety of different animal crossing structures and hydrologic connections that are often overlooked or ignored in many highway construction projects. A unique aspect of this project was the funding for pre-construction monitoring of target species, both terrestrial and aquatic, to gather baseline information on animal populations on both sides of the highway. The data from animal movements and habitat use were used to inform the design of animal and stream crossing structures to ensure that the structures would serve as suitable ecological corridors.