Interstate 90 is the busiest highway through the Cascade Mountains in Washington State, with an average of 27,000 vehicles crossing the pass each day. The Mountains to Sound Greenway landscape follows I-90, and the Greenway portion of it is a federally-designated National Scenic Byway.

The Washington State Department of Transportation began construction in July 2009 on 5 miles of the I-90 Snoqualmie Pass East project, which is the first phase of a major 15-mile upgrade.

Cconstruction will expand this stretch of highway from 4 to 6 lanes, and will incorporate some of the most innovative highway-crossing facilities for wildlife in North America. A series of underpasses will allow water and wildlife to move under the highway, and two vegetated overpasses will assist wildlife in moving safely over the highway. Construction of this first phase is expected to continue until 2015.

Conservationists and Greenway Trust partners have worked for decades to preserve connecting sections of land in the Central Cascades, in the heart of the Greenway. I-90 has been a barrier for wildlife migration, but these improved highway crossings will create safer north-south wildlife crossings and at the same time improve safety for vehicles crossing the pass.

The Greenway Trust has worked with the Washington State Department of Transportation and the I-90 Wildlife Bridges Coalition in support of this project.