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Seattle City Light System Reliability Work to Affect Traffic on I-405

Seattle City Light fiberoptic work will cause rolling slowdowns late at night from September 18-22 on Interstate 405 southeast of Alderwood Mall.

Seattle City Light crews plan to enhance the reliability of the electrical system by pulling in new fiber-optic cables across Interstate 405 approximately two miles southeast of Alderwood Mall. To ensure safe work operations and passage for motorists, crews must intermittently conduct rolling slowdowns of traffic in both directions of I-405.

The work will take place at night beginning Monday, Sept. 18. Traffic will be intercepted and escorted at slow speeds for up to 15 minutes between just southeast of the I-5/I-405 interchange and NE 195th Street as crews install the new fiber-optic cable overhead across the highway. Traffic will return to normal speeds once past the work area. See the map below for details on the differing locations for north and southbound rolling slowdowns. Drivers should expect delays and consider using alternate routes during construction.

Rolling slowdown details:

Occurring nightly from 11:59 p.m. to 4 a.m. beginning Monday, Sept. 18 through the morning of Friday, Sept. 22:

  • Washington State Patrol troopers and contracted crews will intermittently intercept and escort southbound I-405 traffic through the work area beginning southeast of the I-5/I-405 interchange. The same will occur for northbound traffic beginning at NE 195th
  • Traffic using the following on-ramps to I-405 will also be affected: I-5 northbound to I-405 southbound, I-5 southbound to I-405 southbound, NE 195th Street to northbound I-405, State Route 527 northbound to northbound I-405, and State Route 522 to northbound I-405.
  • Should the crews finish in less than four nights, City Light plans to communicate via social media and at this Website:

Customers will benefit from increased electrical reliability. The new fiber-optic lines will provide redundant communication between facilities generating power at City Light’s Skagit hydropower sites, the Bonneville Power Administration, and City Light substations and its system control center.

Seattle City Light’s point of contact for the media is Scott Thomsen, Communications, (206) 615-0978 and Stakeholder (e.g. emergency services) questions can be directed to Mark VanOss, Sr. Public Relations Specialist, (206) 684-3279 and

Map showing affected area of northbound and southbound rolling slowdowns on I-405