SR 18 - Issaquah/Hobart Rd to Raging River Br - Widening

Project news

  • WSDOT held a project team workshop to brainstorm initial design alternatives on July 16, 2020. The project team identified multiple concepts for roadway alignment, median treatments, stream-crossing structures and wall types, and Tiger Mountain summit treatments, among others. The team will use this information to develop preliminary design concepts.
  • In spring 2019, the Legislature approved funding to begin design work on widening SR 18 between Issaquah-Hobart Road and Deep Creek. There is no funding for construction.
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Needs & benefits

SR 18 is a crucial highway that moves thousands of people and serves as an important truck route between western and eastern Washington. Although most of SR 18 from Issaquah-Hobart Road to Interstate 90 is within protected forestlands, the number of vehicles using the highway has increased with more people accessing adjacent recreational areas and as cities and businesses on either end of SR 18 have grown significantly. This has resulted in more frequent congestion and an increase in collisions.

The 5-mile section between Issaquah-Hobart Road and Deep Creek has one lane in each direction, except for alternating truck-climbing lanes. When funded for construction, we will widen this section of the highway to provide two lanes in each direction with a center median or barrier.

Widening the highway presents several challenges. There are up to 17 fish-bearing streams under the roadway and many contain fish barriers that must be eliminated. The corridor has also been subject to historic landslides, contains unstable soils, and other natural resources that must be assessed and considered throughout the design process

Benefits of improving the highway include:

  • Reduced congestion and better travel times.
  • Reduced risk of collisions following installation of a center median or barrier.
  • Upgraded fish passages and wildlife crossings that will provide better habitat for fish and safer movement for wildlife.

As part of a separately funded project extending from Deep Creek to Interstate 90, WSDOT is also improving the highway to provide additional capacity, improve safety and reduce existing congestion. Construction for that project is expected to begin in 2021 and be open to the public in 2023. To learn more, you can visit the project webpage at


  • Spring and summer 2020: Design work and community engagement completed to date:
    • June 11, 2020: TAC meeting No. 1
    • July 9, 2020: TAC meeting No. 2
    • July 16, 2020: Practical design and alternatives identification workshop
  • Design work and community engagement to be completed:
    • TAC meeting No. 3 August 20, 2020
    • TAC meetings 4, 5 and 6 dates TBD
    • EAG meetings 1, 2, 3 and 4 dates TBD
  • Fall 2020: Deliver widening report and cost estimate to State Legislature.
  • Winter 2020 through winter 2021: Ongoing design refinement and community engagement
  • Winter 2021/2022: Funded design work complete.


The Washington State Legislature provided WSDOT with $26 million beginning in the 2019-2021 biennium for SR 18 design work.

This money will be used for:

  • Designing highway improvements. 
  • Completing a cost estimate for widening SR 18 from Issaquah-Hobart Road to Deep Creek. 
  • Acquiring right-of-way. 

There is no funding allocated for construction at this time.

A small map showing the section of SR 18 between Issaquah-Hobart Road and Raging River Bridge in King County, Washington.
Project map area

 A small photo looking east on SR 18 that shows one lane in each direction at the bridge over Issaquah-Hobart Road
Looking east on SR 18 near Issaquah-Hobart Road