The Seattle Department of Transportation (SDOT) advises travelers of the upcoming weekend closures of southbound state Route 99 and eastbound Mercer Street from Friday, March 21, through Sunday, March 23, for construction activities associated with the Mercer Corridor Project. 

These separate closures will accommodate completion of Mercer Street widening and SR 99 bridge replacement work.  

Southbound SR 99 and eastbound Mercer Street will fully close to traffic beginning Friday, March 21, at 11 p.m. for the setting of the SR 99 bridge girders over Mercer Street. 

During the closure:

•Southbound SR 99 will fully close to traffic between Valley Street and the southern end of the Battery Street Tunnel. Traffic traveling through Seattle via SR 99 will be directed to Interstate 5 in North Seattle at North 85th Street. More information about alternate routes during construction may be found at www.seattle.gov/transportation/mercercorridor.htm.

•Eastbound Mercer Street will fully close to traffic between Fifth and Dexter avenues North. Traffic heading east toward I-5 from Queen Anne will detour to Fifth Avenue to either Denny Way to access southbound I-5 at Yale Avenue or through downtown on Fifth Avenue to access northbound or southbound I-5.

•The sidewalk on Mercer Street will also close between Fifth and Dexter avenues. Pedestrians will detour to Broad Street.

Early warning signs will be available in advance of the SR 99 lane restrictions and Mercer Street detours. Travelers can expect significant traffic and delays and should plan ahead and use alternate routes.

Access to Seattle Center from I-5 via westbound Mercer and Broad streets and from southbound SR 99 at Valley Street will open through the weekend, but travelers should expect delays.

Southbound SR 99 will reopen midday Saturday, March 22; eastbound Mercer Street between Fifth and Dexter avenues will remain closed until about 6 p.m. on Saturday, March 22.

After crews complete the setting of the SR 99 bridge girders over Mercer Street, southbound SR 99 will reopen to traffic around noon on Saturday, March 22. Eastbound Mercer Street will remain closed between Fifth and Dexter avenues through about 6:00 p.m. on Saturday, March 22.

SR 99 will remain closed south of Denny Way for Alaskan Way Viaduct-related work from 4:30 a.m. to 7 p.m. on Saturday, March 22.