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Crews installing ground monitors for SR 99 Tunnel Project

As the Washington State Department of Transportation (WSDOT) reported last week, crews started installation of underground monitors along the State Route 99 tunnel route. The underground monitors are part of a comprehensive program to help mitigate potential ground movement and protect structures during tunneling, which is scheduled to begin this summer.

While most of the tunneling will take place deep beneath downtown Seattle in terrain that is very dense and stable, WSDOT will install more than 700 instruments under streets and sidewalks to track ground movement that may occur during tunneling. You can find more information about the monitoring equipment in this WSDOT folio published in September 2012.

This week, southbound First Avenue has been reduced to one lane between Union and University streets to give crews the space they need to install several ground monitoring devices. Additionally, parkingwill be restricted as needed. Signs will direct drivers around the closures. The work will not affect access to parking lots, buildings and driveways.

Drivers can expect similar lane closures on First Avenue between University and Virginia streets through February. Traffic control will be maintained 24/7 until the work is completed in late February.

Travel impacts

  • Wednesday, Jan. 30 – Saturday, Feb. 2 – Southbound First Avenue between Union and University streets reduced to one lane 7 a.m. Monday to 10 p.m. Saturday.
  • Two northbound First Avenue travel lanes will be open at all times.

Parking impacts

  • Wednesday, Jan. 30 Saturday, Feb. 2 – Parking on the east side of the street will be closed from 7 a.m. Tuesday to 10 p.m. Saturday.

Plan before you go; visit the following website for updated traffic conditions and potential impacts:

SR99 / Alaskan Way Viaduct Replacement Project advisories and updates are available at