Seattle Tunnel

Category Roads and Bridges
Location Seattle, WA
Owner WSDOT

This $1 Billion project consists of 8,800 feet of bored tunnel to replace the existing Alaskan Way Viaduct. The Bored Tunnel will follow a large radius curve beginning just south of S. Washington Street, and then pass under Western Avenue to be parallel with First Avenue. The first 500 feet of the Project includes a depressed roadway that contains mainline SR 99 and southbound-off and northbound-on ramps. The roadway structure inside the Bored Tunnel will stack the roadways with two southbound lanes on the upper level and two northbound lanes on the lower level. A South Tunnel Operations Building, located east of SR 99 between S. Dearborn Street and S. King Street, will provide ventilation as well as maintenance and operation capabilities. There will be a North Tunnel Operations Building on the east side of Sixth Avenue N. between Thomas Street and Harrison Street. Inspections include soil density, sieve analysis, reinforced concrete, reinforcing steel, structural steel, welding and ultrasonic testing.