SR 518 - SR 509 to I-5 - Corridor Planning Study

A map showing the scope of the SR 518 Corridor Study from I-5 to SR 509Study Report

Final Report (pdf 5 mb)

Study Appendices (pdf 38 mb)

Study Purpose

State Route 518 is an important east-west link for Burien and the surrounding communities to the I-5/I-405 interchange. It serves residents and businesses along the corridor, substantial commerce and freight, and heavy vehicle traffic into and out of Seattle-Tacoma International Airport via the North Airport Expressway (NAE).

In 2017, between 73,000 and 131,000 vehicles used SR 518 every day. Due to considerable growth in nearby communities and the airport, WSDOT expects increased demand and delays at peak travel times. For this reason, SR 518 is a candidate for potential near-term and long-term transportation improvements that will benefit all users of the highway.

Through this study, WSDOT:

  • Determined priorities for future highway work or transit service adjustments.
  • Developed practical, cost-effective concepts to help improve trip reliability and safety along the corridor

WSDOT study partners included: Burien, Des Moines, SeaTac, Tukwila, tribes, King County Metro, the Port of Seattle, and Sound Transit. Concepts identified in the study were submitted to the Legislature in May 2020.

Community Engagement

With the help of our partners, WSDOT gathered feedback and ideas about SR 518 from local stakeholders and community members via an online survey.

The End Result

The information gathered during this study will help WSDOT and its study partners prioritize practical concepts that will:

  • Improve travel reliability on the SR 518 corridor.
  • Provide more transportation options for corridor users.

Concepts were prioritized based on user feedback, data-driven safety benefits and cost effectiveness. This effort focused on finding smaller fixes and operational adjustments first so they can be implemented as funding becomes available. This may delay or remove the need for additional and more costly future improvements.

Study Timeline

Fall 2018

  • Engage with key stakeholders and nearby communities.
  • Gather corridor user feedback through an online survey.
  • Collect and analyze survey responses.

Winter - Summer 2019

  • Develop practical concepts based on community input.
  • Share developed concepts with public and gather additional feedback.

Fall - Winter 2019

  • Compiled and edited study report.

Summer 2020

  • Submitted study report to the Legislature.


The Washington State Motor Vehicle Account provided $500,000 and the Port of Seattle contributed an additional $400,000 for the corridor study. Funding for concepts identified in the study is not currently available.

Your feedback is important

Please contact us with questions or comments about this corridor study:

Thomas Noyes
Senior Transportation Planner