West Marginal Way SW Safety Corridor Project

Updated March 24, 2023

What's Happening Now?

Construction to begin on West Marginal Way SW Safety Corridor Improvements Project in early April

Please see the Construction Notice for more details. 

Through collaboration with the community, we identified safety improvements on West Marginal Way SW as a priority for all travelers, especially people biking and walking, as a way to cross the Duwamish River during the West Seattle High-Rise Bridge closure. As we engaged local businesses and people who drive large trucks, we heard a strong interest in making driveway access movements safer and speeds slower.

The West Marginal Way SW Safety Corridor Improvement Project increases awareness of driveways crossing the Duwamish Trail. It also adds a nearly half-mile long on-street protected bike lane (PBL) between Marginal Pl SW and the existing Duwamish Trail signalized crossing near SW Idaho St, closing a crucial gap in the regional walking and biking network. When complete, West Marginal Way SW will be a more predictable space for all travelers. 

Project Background

West Marginal Way SW connects communities and industrial businesses along the western bank of the Duwamish Waterway. It is a Major Truck Street between bridges and connects to Port of Seattle facilities. The street also provides direct access to the Duwamish Longhouse and Cultural Center, parks, and residences as well as shipping, manufacturing, and industrial areas. The Duwamish Trail, a multi-use recreational path for people walking and biking, runs alongside West Marginal Way SW for several miles.

This project is designed to make the street safer, more convenient, and more comfortable for everyone, and encourage people walking and biking - our vulnerable users - to use West Marginal Way SW. Each of these improvements can bring us closer to our Vision Zero goals and help to provide alternatives for the traveling public that reduce demands on the road network.

Planned Street Redesign

Diagram illustrating the planned street redesign for West Marginal Way Southwest. It includes a 6-foot walking path protected from the street a 5-foot strip with trees, next to that is an 8-foot bike lane protected from traffic by a 3-foot wide concrete barrier, they the road includes a 12-foot driving lane, an 11-foot center turning lane, two more driving lanes, on 10-feet wide and one 12-feet wide with an 8-foot wide planting strip next to it.

Moving freight and goods remains the priority for this major truck street which serves port facilities, cargo yards, and major businesses. We carefully considered this distinction and the importance of maintaining freight reliability during the high bridge closure as we developed the new street design and implementation timeline.

The planned street redesign project will enhance safety for everyone by encouraging slower driving speeds, eliminating high-speed passing, improving visibility for people entering from side streets, and improving the predictability of all people using the West Marginal Way SW corridor. The project will further separate vulnerable people from faster-traveling traffic and trucks and will connect the Duwamish Trail with The West Seattle Bridge Trail.

This comes after months of engagement with key stakeholders, including our bicycle and freight advisory boards, transportation safety advocates, local businesses, community groups and members, the Port of Seattle and maritime industrial community, and the West Seattle Bridge Community Task Force. The feedback we received from these various groups was mixed. Some asked for the bike lane to be installed in 2021 while others requested installation after the West Seattle Bridge was open to traffic again. We also considered the Freight Master PlanBicycle Master Plan, our Vision Zero and mode shift goals and data to inform our decision.  

Protected Bike Lane 

The 0.6-mile two-way protected bike lane and parking lane will be built on the western side of the street in the southbound lane that begins south of the Chelan 5-way intersection and bridge structures that limit the capacity to West Marginal Way SW.  Redesigning the extra lane, that does not go all the way through the corridor, leads to a smoother and more predictable trip for people driving without unnecessary merging, eliminates high-speed passing, or the need to navigate around slower moving bicycles.

The new bike lane will complement the new sidewalk north of the Duwamish Longhouse and Cultural Center and the walking and biking crossing signal at the Duwamish Longhouse built in fall 2021.

Bike lane project area

Highland Park Way and West Marginal Way Intersection 

In fall 2021, we completed improvements to make the intersection accessible, efficient, and safe:

  • Removed existing raised traffic islands and created a new northbound lane.
  • Shifted the southbound left-turn lanes farther west, providing enough space in the intersection to allow the westbound right turning vehicles (of all sizes) to go at the same time. This improvement will help to reduce wait times at the intersection.  
  • Updated the traffic signal equipment for people of all abilities and installed the infrastructure to allow us to make signal adjustments in real-time remotely from our Transportation Operations Center.
  • Installed new wheelchair-accessible curb ramps in compliance with the Americans with Disabilities Act.
  • Relocated the westbound bus stop.
  • Improved turning movements for people driving through the intersection to shorten wait times.

Duwamish Longhouse: New walking and biking signal, new marked crosswalk, and new sidewalk

People driving fast and higher traffic volumes on West Marginal Way SW can create safety challenges for people trying to access the Duwamish Longhouse. In December 2021, we installed a new, interim crossing signal that stops traffic for people walking and biking who need to cross West Marginal Way SW. A permanent crossing signal is being designed and is scheduled to be installed after the reopening of the West Seattle Bridge.    Graphic showing the Duwamish Longhouse project on West Marginal Way

Pedestrian safety improvements at the Duwamish Longhouse include a new pedestrian signal, crosswalk, and sidewalk.

Traffic Mitigation 

We made recent improvements to clarify roadway operations as well as encourage good driving habits.   

  • Added a traffic island at West Marginal Way SW in front of SW Front St.  
  • Added white, flexible posts to divide the right turn lane at West Marginal Way SW leading to the on-ramp to the 1st Ave S. Bridge.   

Traffic island and white flexible posts on West Marginal Way SW

(Left) West Marginal Way SW traffic island just north of SW Front St​ and (right) white, flexible posts to divide travel lanes


We are committed to Vision Zero goals of reducing people speeding and injury and fatality crashes in Seattle. In 2020, we installed six speed radar signs along West Marginal Way SW to help reduce travel speeds from 40 mph to 30 mph. We found that the radar feedback signs corresponded with people reducing their vehicle speeds by up to 11% so far.  

Project Timeline 

Early 2021

  • Engaged with area businesses, community partners, and neighbors.
  • Conducted outreach with businesses along West Marginal Way via online business survey
  • Sent a mailer to West Seattle residents about how to give input.  
  • Held a virtual open house. 

Spring 2021

  • Compiled and analyzed feedback

Summer 2021

  • Shared preferred design option with the community.
  • Announced decision to build protected bike lane after the high bridge reopens.

Fall 2021

  • Completed improvements at the West Marginal Way SW and Highland Park Way SW intersection.
  • Built a new sidewalk and finished the Duwamish Longhouse interim crossing signal.  
  • Announced decision to build protected bike lane after the high bridge reopens.

September 2022

  • Reopened the West Seattle Bridge

October - November 2022

  • Conduct further data collection and analysis on West Marginal Way SW  

    Community Engagement  

    We are committed to working with the community to keep you informed of progress and milestones as we rehabilitate the bridge. We will seek your continued feedback on how to improve mobility and safety for West Seattle, as well as the South Park and Georgetown neighborhoods. Thank you to everyone who has helped us make this project better with your ongoing engagement. 

    Learn more, get involved, and tell us what you think:

    Watch our project video, available in multiple languages:

    Project Materials

    Update to community (May 2022)

    Bike lane decision blog announcement (7/14/21)

    Watch the open house on YouTube (2/18/21)

    Open House PowerPoint Presentation (2/18/21)

    Open House Summary (2/18/21)

    West Seattle Transportation Coalition Meeting Presentation (1/28/21)

    Project mailer (English - 1/21) 

    Translated project information

    West Marginal Way Business Survey (2/4/2021)

    Past Outreach Activities


    Greg Spotts, Director
    Address: 700 5th Ave, Suite 3800, Seattle, WA, 98104
    Mailing Address: PO Box 34996, Seattle, WA, 98124-4996
    Phone: (206) 684-7623

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    The Seattle Department of Transportation (SDOT) is on a mission to deliver a transportation system that provides safe and affordable access to places and opportunities for everyone as we work to achieve our vision of Seattle as a thriving, equitable community powered by dependable transportation.