From the Washington State Department of Transportation:
From Friday, May 13 until the morning of Monday, May 16
Both directions of SR 99 between the West Seattle Bridge and Battery Street Tunnel will be closed from 11 p.m. Friday, May 13 to 5 a.m. Monday, May 16. Northbound SR 99 will reopen between S. Royal Brougham and the Battery Street Tunnel at noon on Saturday, May 14.
From Monday, May 16 until 2013
Both directions of the southern mile of the viaduct corridor will be reduced from three to two lanes between the West Seattle Bridge and Seattle’s sports stadiums. This lane configuration will remain in each direction through 2013 and possibly longer, until the central waterfront section of the viaduct is replaced.
See WSDOT’s construction Web site.