12th Ave NW & SR-900

12th and SR-900

Project Overview 

This project will widen the northbound SR 900/17 Avenue NW approach to 12th Avenue NW to construct an exclusive right-turn lane and widen 12th Avenue NW approach at SR 900/NW Sammamish Road to provide an additional left-turn lane for added capacity.

Improvements will also include new protected bike lanes, wider sidewalks, landscaping, trees, and illumination on both sides of 12th Avenue NW. 


Roadway network updates are necessary to improve overall traffic circulation north of I-90. These improvements help reduce the number of intersection accidents by providing the dedicated right-turn lane from SR 900/17th Avenue to 12th Avenue. The project will also help reduce the number of vehicles waiting to turn left from 12th Avenue at any given time by providing and additional left-turn lane.

The project is also a corridor identified in the City’s Walk and Roll Plan to increase accessibility for pedestrian and bicycle traffic and connect existing non-motorized facilities throughout the City. This project is included in the Central Issaquah Area Plan, the City's Concurrency Capacity Projects list and is part of the Costco Development agreement. The project is partly funded by a Transportation Improvement Board (TIB) grant.

Traffic Changes

During the project, traffic on 12th Ave NW will be restricted to one way and one lane of traffic coming from 17th Ave NW/SR-900. A detour will be in place that utilizes Lake Drive, 11th Ave NW and NW Sammamish Road. Large delivery vehicles may want to avoid 12th Ave NW during construction as it will be more difficult to access with the roadway being limited to one lane of traffic

Parking lot entrances to businesses will remain open throughout the project.

Be sure to use extra caution when driving through the construction zone.

Project Timeline

  • Fall 2021: Design completion and permitting
  • Early 2022: Project bid and award
  • April 2023: Construction begins
    • April-August 2023: Stage 1 Construction – work on south and west side of 12th Ave
    • August-November 2023: Stage 2 Construction – work on north and east side of 12th Ave
  • November 2023: Anticipated construction completion

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