12th Ave NW & SR-900

12th Ave and SR900

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 protected bike lanes, sidewalks, and illumination along 12th Avenue NW. 


This project is required as part of the Costco Development agreement and is included in the Central Issaquah Area Plan and the City's Concurrency Capacity Projects list. Roadway network improvements are necessary to support the non-residential property and improve overall traffic circulation north of I-90. These improvements also help reducing the number of intersection accidents and the number of vehicles waiting to turn left from 12th Avenue at any given time, helping reducing fuel emissions.

As a requirement of the Costco Development agreement, the City is responsible for 52% of the project costs and Costco is responsible for 48% of the project costs. State grant funding has been secured for design and Right of Way acquisition. The City will also apply for Transportation Improvement Board (TIB) grant funding and if successful use the grant funds towards construction. 

Project Timeline

  • May 2020: Design work begins
  • January 2021: 30 % Design
  • June 2021: 60 % Design
  • September 2021: 90 % Design
  • Fall 2021: Right of Way acquisition and permitting
  • Early 2022: Project advertisement and award
  • TBD: Construction

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