Mercer Corridor Improvements

Seattle, Washington


Clearing clogged streets, uniting neighborhoods


For more than 40 years, the Mercer Corridor was one of Seattle’s most significant transportation challenges. It divided neighborhoods, isolated destinations from nearby residences, clogged city streets, hindered economic development and created hazardous traffic backups on I-5. Every day the street grid made it difficult for more than 100,000 people — pedestrians, bicyclists, transit users, truck drivers and motorists — to connect to places where they live, work and socialize.

The Mercer Corridor Improvement project was a two-phase project initiated by the City of Seattle’s Department of Transportation to convert the former Mercer/Valley Street one-way couplet to a two-way operation between I-5 and Dexter Avenue South. 

The project improved mobility and safety by providing multimodal connections to and through the South Lake Union neighborhood. It widened Mercer Street to create a two-way boulevard, reconstructed Valley Street as a local access street, provided new and wider sidewalks, improved connections to transit and added bicycle lanes. The project replaced major utility infrastructure and integrated many environmentally friendly and sustainable design features.

HNTB served as construction manager on the project, providing field inspection services and a full suite of construction-management services, including pre-construction planning, project controls, office engineering, field inspection, post-construction services and public involvement.