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Mercer Corridor Project

If you need this information translated, please call (206) 733-9990.
Si necesita traducir esta información al español, llame al (206) 733-9990.

The Mercer Corridor stretches from Interstate 5 to 5th Ave. W, and has been one of the City of Seattle’s most significant transportation challenges for over 40 years. SDOT is committed to improving the Mercer Street Corridor by 2016.

Learn more about the Mercer Corridor Project or subscribe to email alerts.

Last updated  08/18/2015

Signal improvements at 5th Ave. N, Broad St., and Thomas St. are complete!

Please be mindful of the following:

  • Thomas St. now open at 5th Ave. N.
    • Drivers traveling west on Thomas St. have the option to turn right or left onto 5th Ave. N.
    • Drivers turning left from Thomas St. may also access Broad St. toward the Elliott Bay Waterfront.
    • The relocated driveway on the west side of 5th Ave. N at Thomas St. is open for deliveries to the Seattle Center Campus.
  • All pedestrian crosswalks in this area are open.
  • Pedestrians crossing the Seattle Center driveway at Thomas St. should watch for the signal and only cross the driveway when the walk sign is on.  
  • Eastbound Broad St. will continue to operate with two left-turn lanes at 5th Ave. N (no right turns allowed).
  • Please be mindful of changes and send any questions to

What's next?

  • The Mercer West Project will install a large stormwater detention pipe in Roy St. between 4th Ave. N and 5th Ave. N in September and October. This is recently added work that provides stormwater detention for the area including the Washington State Department of Transportation's (WSDOT's) construction at the future SR 99 tunnel north portal.

Roy St. will be fully closed to vehicles and cyclists between 4th Ave. N and 5th Ave. N as crews install a stormwater detention system. Crews will work weekdays from 7 a.m. to 4 p.m. Construction is expected to last between 6 and 8 weeks. Anticipated impacts include:

  • Vehicles and cyclists traveling on Roy St. will be detoured south to Mercer St. between 4th and 5th avenues.
  • Local access will be maintained to the alley on the south side of Roy St. between 4th and 5th avenues via eastbound Roy St. The alley will be southbound only during this closure. Please obey all closure and detour signage.
  • Street parking will be restricted on this block while work is completed. 
  • Pedestrian access will be maintained on the south sidewalk along Roy St.

Map of Roy St. closure

Looking ahead

  • Intermittent lane closures will continue through fall as crews complete miscellaneous improvements throughout the project area. Closures will be temporary, localized, and occur during non-peak hours, Monday through Friday.
  • Adaptive signal control is under design and expected to be installed on Mercer Street in 2016. The new system will be more responsive to traffic conditions, but will still be limited by the capacity at the I-5 on-ramps during the peak periods.

Look at what we’ve accomplished so far! Read more here.


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