Major Construction on Mercer West to Begin: Weekend closure of SR 99 and Mercer Street

Posted on May 13 2013 12:25 PM

The weekend of May 17-20, the Seattle Department of Transportation (SDOT) will begin major construction on Mercer West by preparing to demolish the eastern half of the SR 99 bridge over Mercer Street and widen Mercer Street between Fifth Avenue N and Dexter Avenue N.

When completed, the West Phase of the Mercer Corridor Project will provide a direct connection from I-5 and the new SR 99 Tunnel to Uptown, the Seattle Center, and neighborhoods to the west. In addition to widening Mercer Street for two-way traffic, the project includes improved pedestrian connections, a bike path between Dexter and Fifth avenues North, replacement of the SR 99 bridge over Mercer Street, and signal and channelization modifications to make Mercer and Roy streets two-way through the Uptown area.

In preparation for construction, SR 99 will be fully closed to traffic the weekend of May 17-20 to allow crews to complete traffic shifts on SR 99 and Mercer Street.

Weekend work on SR 99 and Mercer Street: Friday, May 17, through Monday, May 20

SR 99 will be fully closed to traffic beginning Friday, May 17 at 11 p.m. through Monday, May 20 at 5 a.m. During the closure:

  • SR 99 will be fully closed between Valley Street and the southern end of the Battery Street Tunnel. Traffic traveling through Seattle via SR 99 will be directed to I-5 north of Seattle at 85th Street or south of Seattle at E Marginal Way.
  • Mercer Street will be fully closed to traffic between Fifth Avenue N and Dexter Avenue N. Traffic heading east towards I-5 will be detoured to Denny Way at Fifth Avenue N and will reconnect to Mercer Street at Dexter Avenue N to continue east.
  • Sidewalks on both sides of SR 99 between Thomas and Valley streets and on the south side of Mercer Street between Fifth Avenue N and Dexter Avenue N will be closed.


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

Major Mercer and SR 99 impacts begin Monday, May 20

Following the full weekend closure of SR 99, lane restrictions on Mercer Street will remain in place between Fourth Avenue N and Ninth Avenue N as crews begin construction on the new SR 99 overpass and widening Mercer Street to the south. Roadway impacts will include:

  • Mercer Street will be reduced to two eastbound lanes between Fourth Avenue N and Ninth Avenue N.
  • SR 99 traffic will be shifted to the west side of the roadway between Valley and Harrison streets. Two lanes will remain open in each direction.
  • The northbound SR 99 off-ramp to Mercer Street will be permanently closed. A new signalized intersection at Republican Street and Dexter Avenue N will be available for northbound SR 99 traffic to reach South Lake Union.
  • Local access to Taylor Avenue N via Mercer Street will be maintained.
  • Sidewalks on Mercer Street will be impacted during this work. The sidewalk on the north side of Mercer Street will be closed between Fifth Avenue N and Dexter Avenue N. The sidewalk on the south side will remain open to pedestrian traffic.


To help alleviate traffic congestion during Mercer Street lane restrictions, Broad Street will be re-opened to eastbound traffic on Monday, May 20, as an alternate route to reach I-5.

Additionally, signal modifications will be made at the intersections of Fifth Avenue N and Harrison Street, and Harrison Street and Broad Street to allow for southbound Fifth Avenue N traffic to turn left onto Harrison Street and connect to eastbound Broad Street.

Lane reductions on Mercer Street will continue throughout the West Phase of the Mercer Corridor Project, which is anticipated to be completed in mid-2015. Construction of this $95 million project will take approximately 2.5 years.

Alternative route information available for Mercer Street lane restrictions

A map illustrating Mercer Street lane restrictions and alternative routes beginning May 20 is available online at:

If you have questions regarding this work, please contact the Mercer Corridor Project hotline 206-419-5818 or email the project at