New Diverging Diamond Interchange at I-90SR 18 Now Open

The Washington State Department of Transportation (WSDOT) opened a diverging diamond interchange at the I-90/SR 18 junction on July 25, enhancing traffic flow and safety. This innovative design shifts traffic to the left side, allowing vehicles to travel beneath I-90 without making left turns across oncoming traffic. The new configuration followed an eight-day closure of SR 18 to complete construction. Key updates include synchronized traffic signals, fresh lane markings, and salmon-colored concrete islands that separate traffic. The interchange upgrade is part of a larger $188 million project to widen SR 18, expected to ease congestion and improve freight movement.

Upon completion in late 2025, this stretch will feature two lanes in each direction. Additionally, the project removes six fish barriers to support salmon migration and creates wildlife corridors for safe animal passage. Construction began in fall 2022, with full project completion anticipated by late 2025.