In January 2009 officials from the state, county, city, and port recommended a bored tunnel to replace the waterfront section of the viaduct - the only option that would allow the state highway to remain open during construction.
Foundations for the new side-by-side roadway were sunk up to 260 feet (79 meters) deep for added stability, and wider lanes and shoulders were provided. In 2007, officials decided to replace the southern end of the viaduct while continuing to consider options for replacing the waterfront section. The seawall was in disrepair, and the soil it supported around the viaduct’s foundations was subject to liquefaction. Repairs to the viaduct, well into its 75-year design life, cost more than $14 million. Engineers said the viaduct was within a few seconds of complete collapse. A similar viaduct in Oakland was destroyed by the 1989 Loma Prieta earthquake, and in 2001 the Nisqually earthquake damaged the viaduct and its supporting seawall. This double-decked elevated section of State Route 99 runs along Elliott Bay in Seattle’s downtown and Industrial District.įifty years later, the viaduct was carrying more than 100,000 vehicles per day - but its vulnerabilities had become obvious. One of two major north-south corridors through Seattle, the Alaskan Way Viaduct went into service in 1953.
