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

Project news

  • WSDOT provided the preliminary preferred alternative to the State Legislature during its 2021 session. During the session, the design was revised to lower total costs and reach specified funding targets.
  • The technical advisory committee met for the fifth time in August to discuss the revised preliminary preferred alternative, ask questions about the updated design, and discuss the next steps.
  • Sign up for the WSDOT newsletter to receive weekly email updates about state highway projects in King County. 

Needs & benefits

SR 18 is a crucial highway that moves thousands of people and serves as an important truck and commuter 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. Cities and businesses on either end of SR 18 have also 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, plus alternating truck climbing lanes. When funded for construction, WSDOT will widen this section of the highway to provide two lanes in each direction with a center median or barrier. Widening of 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, which will provide better habitat for fish and safer movement for wildlife.

As part of a separately funded project extending from Deep Creek to I-90, WSDOT is also improving this eastern end of the highway corridor to provide additional capacity, improve safety and reduce existing congestion. Construction for that project is expected to begin in 2022 and be open to the public in 2024. To learn more, you can visit the project webpage at:


  • Design work and community engagement completed to date.
    • June 11, 2020: Technical Advisory Committee (TAC) meeting number one
    • July 9, 2020: TAC meeting number two
    • July 16, 2020: Practical design and alternatives identification workshop
    • Aug. 20, 2020: TAC meeting number three
    • Sept. 17, 2020: Performance rating workshop
    • Sept. 24, 2020: TAC meeting number four
    • Nov. 19, 2020: Announcement of the preliminary preferred alternative
    • Nov. 19, 2020: Executive Advisory Group (EAG) meeting number one
    • Aug. 25, 2021: TAC meeting number five
    • Oct. 13, 2021: EAG meeting number two
  • Design work and community engagement to be completed:
    • Conceptual engineering and plan development
    • TAC meeting number six: date TBD (optional)
    • EAG meetings three and four: dates TBD (optional)
  • Winter 2020 through winter 2021: Conceptual design and plan development, and community engagement.
  • Winter 2021/2022: Contracted 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