SR 99 - NB Duwamish River Bridge - Select Grid Deck Replacement

Project news

  • Construction started July 26, 2020. Expect northbound nightly lanes reductions Sundays through Thursdays on northbound SR 99 through September and plan for detours.
  • The next overnight northbound SR 99 full closures are scheduled for Sept. 8-10.
  • While the northbound SR 99 Duwamish River Bridge is closed at night, the Spokane Street (lower) Bridge is open to all traffic overnight only.
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Needs and benefits

Several of the panels that make up the deck of the northbound SR 99 Duwamish River Bridge, commonly known as the 1st Avenue South bridge, need to be replaced to keep the bridge in a state of good repair. This highway is a critical route between cities like Burien, Normandy Park and SeaTac, and Sea-Tac Airport toSeattle, carrying about 62,000 vehicles each day.

During summer 2020, WSDOT contractor crews will replace 14 grid deck panels on the northbound SR 99 Duwamish River Bridge. This will help increase traction on the bridge and provide a smoother, safer ride for travelers. Also, replacing the grid deck panels helps preserve the bridge structure and reduces the need for costly emergency repairs.


  • December 2019: Project was advertised for competitive bidding.
  • January 2020: Project awarded to C.A. Carey Construction.
  • July 26, 2020: Construction began.
  • Fall 2020: Construction is scheduled to be complete.


Financial Data for PIN 109926Y
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $1,257
CWA $0
Total $1,257


Tom Pearce
WSDOT Communications

A small map showing the location of the SR 99 Duwamish River Bridge select grid deck replacement project.