West Marginal Way SW Safety Corridor Project

Updated June 28, 2023

What's Happening Now?

West Marginal Way SW Safety Corridor Improvements – A Data-Driven Safety Project

In May of 2023 we completed installation of a 0.4-mile two-way on-street protected bike lane (PBL) and striping on the western side of the corridor between SW Marginal Pl and Duwamish Longhouse and updated all 17 Duwamish Trail / driveway crossings on the east side of the corridor with signs and pavement markings.

Work on the 0.4 protected bike lane on SW Marginal Way

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 travelers from faster-traveling traffic and trucks and will connect the Duwamish Trail with The West Seattle Bridge Trail.

These improvements come after months of engagement with key stakeholders, including our Port of Seattle and maritime industrial community, bicycle and freight advisory boards, transportation safety advocates, local businesses, community groups and members, and the West Seattle Bridge Community Task Force. 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 

In July 2021, we announced the construction of a new bike lane when the West Seattle Bridge reopened. Our approach to designing this project is data-driven and incorporates the input of people who use West Marginal Way SW. We first collected data and completed an analysis of potential impacts in 2020. After the West Seattle Bridge reopened in September 2022, we updated the data.

For this project, we conducted data collection on West Marginal Way SW four times and closed the southbound curbside travel lane for 0.4-miles of the 2.5-mile corridor (from SW Marginal Pl to the Duwamish Longhouse) for 2 weeks in Fall 2022 to better understand the traffic impacts to people driving cars and trucks about our proposal to reuse one southbound travel lane for a Protected Bike Lane. 


  • Driver travel times increased by about 2 seconds per trip along the corridor
  • Driver speeds dropped from 43 to 37 mph (12% decrease – posted speed limit is 30 mph)
  • It varies seasonally, but on average there are between 100 to 200 people walking and biking per day

For more information on the data collection, please visit SDOT’s blog.

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.    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 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.

August/September 2022

  • Data collection and safety assessment for all driveways and intersection along the east side of the corridor where the Duwamish Trail crosses

September 2022

  • Reopened the West Seattle Bridge
  • Data collection and analysis

October - November 2022

  • Conducted data collection of driver volumes/speed and walking/biking counts on West Marginal Way SW from October 23 to November 6.

December 2022

  • Duwamish Trail vegetation overgrowth clearing

January 2023

  • Temporary Protected Bicycle Lane (PBL) installed for the Low Bridge detour route

February 2023

  • Conducted public engagement for the project

April-May 2023

  • Installation of a two-way protected bike lane and striping on the western side of the corridor between SW Marginal Pl and Duwamish Longhouse

Summer 2023

  • Monitor project area and evaluate performance

Fall 2023

  • Report back on data collection findings

Community Engagement  

We are committed to continue working with the community on enhancing safety along West Marginal Way SW and we will continue providing updates. 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.