The original purpose of Seattle one-way Mercer Street was to provide temporary access to Interstate 5 while the freeway was under construction. Forty years later, it was one of the city's most notorious bottlenecks — clogging city streets, hindering economic development and creating hazardous traffic backups, among other issues. The Seattle Department of Transportation looked for the two-phase Mercer Corridor Improvements project to open up east-west traffic between I-5 and the Port of Seattle, becoming a gateway that would support ongoing economic development and provide direct access to the waterfront via Seattle Center, a 74-acre park, arts and entertainment area.

HNTB served as construction manager on the Mercer Corridor Improvement project which converted the former Mercer/Valley Street one-way to a two-way operation between I-5 and Dexter Avenue South. The two-way corridor now provides pedestrians with access to the city’s streetcar, and bicyclists can travel a mile of new bike lanes and six blocks of multiuse trails. The project also replaced major utility infrastructure and integrated many environmentally friendly and sustainable design features.

As many as 15 other construction sites were active in the area during both phases of the Mercer Corridor construction. As construction manager, HNTB headed up clusters of stakeholders, worked with private developers, helped the city decide how to stage work and distributed information to the public to inform corridor users about street closings, detours and construction schedules.

The Mercer Corridor Improvements project was delivered to the city under budget and has enabled significant growth in the South Lake Union area. 

Location: Seattle, WA

Client: City of Seattle’s Department of Transportation

Services: Construction Management