The Alaskan Way/SR 99 Viaduct was built in the early 1950's. It serves as an important bypass for downtown Seattle and takes some of the load off of Interstate 5. As it also cross-connects with the West Seattle Freeway it is an important connector to West Seattle.
The viaduct became a cause for concern after the collapse of the Cypress viaduct in the 1989 San Francisco earthquake. These concerns increased after the 2001 Nisqually Earthquake damaged the viaduct further.
Current plans focus on either rebuilding or replacing the viaduct with a boulevard or tunnel. Along with this project the city seawall will need to be rebuilt as well. What will happen remains in the air: the preferred replacement is a tunnel but the cost-up to 4 billion is hard to account for in the current political and economic climate.
Viaduct in March, 2006