West Marginal Way SW Improvements

Updated July 14, 2021

What's Happening Now?

We'll build a new bike lane on West Marginal Way SW after the West Seattle Bridge reopens to traffic in mid-2022.

  • The new bike lane will complete the all-ages-and-abilities network between South Park and the West Seattle Bridge Trail and beyond, including Alki, the Junction, downtown Seattle, and SODO. It will also enhance safety for everyone along West Marginal Way SW.
  • Starting this weekend, people traveling the detour route at West Marginal Way SW and Highland Park Way will see us improving the intersection to make it more accessible. This includes a new northbound lane.
  • This announcement also comes after comprehensive traffic data analysis, which predicts that adding the new bike lane will have minimal effects on the number of trucks that can use the street and how long it takes to drive in the area.
  • Today, West Marginal Way SW has 3 travel lanes (2 northbound and 1 southbound) and a center turn lane that extend through the full length of the corridor. All three continuous lanes, as well as a center turn lane, will remain open to through traffic until project implementation in 2022.

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 maintenance centers. The Duwamish Trail, a multi-use recreational path for people walking and biking, runs alongside West Marginal Way SW for several miles.

Since the closure of the West Seattle High-Rise Bridge in March 2020, we have seen an increase in the number and speed of people driving on this busy corridor. Due to this detour, average weekday traffic volumes on West Marginal Way SW have increased by over 150%, from 9,760 vehicles to 24,880 vehicles on an average weekday. 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. 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

Graphic showing the lanes on West Marginal Way

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 will further separate vulnerable people from faster-traveling traffic and trucks. This project will also enhance safety for everyone driving 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 West Marginal Way SW.

This announcement 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 this year while others requested installation after the high bridge reopens to traffic in mid-2022. We also considered the Freight Master PlanBicycle Master Plan, our Vision Zero and mode shift goals and data to inform our decision.  

We anticipate installation of the new street design by mid-2022. Work can occur on weekends, reducing impacts to freight and general traffic. We expect to maintain one lane of travel in each direction, and to keep nearby driveways open during most of the installation.

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 complements the new sidewalk north of the Duwamish Longhouse and Cultural Center and the walking/ and biking crossing signal at the Duwamish Longhouse scheduled to be installed this year.

Bike lane project area

Highland Park Way and West Marginal Way Intersection 

Starting the weekend of July 17-18, 2021, people traveling through the intersection of West Marginal Way SW and Highland Park Way will see us building improvements to make it more accessible, efficient, and safe. This includes a new northbound lane. We have a few plans for the intersection. We will:

  • Remove existing raised traffic islands to create a new northbound lane and shift the southbound left turn lanes farther west to reduce wait times.
  • Update the traffic signal equipment for people of all abilities, which will allow us to make signal adjustments in real-time remotely from our traffic operations center based on what cameras show
  • Install new accessible curb ramps
  • Relocate the bus stop
  • Improve turning movements for vehicles traveling through the intersection to shorten wait times

Our construction will minimize impacts to the traveling public as much as possible. 

Graphic showing the intersection improvements

Duwamish Longhouse: New pedestrian signal, new crosswalk, and new sidewalk

Speeding vehicles and higher traffic volumes on West Marginal Way SW can create access and safety challenges for people trying to access the Duwamish Longhouse. In 2021, SDOT will build an interim pedestrian signal and painted crosswalk at the Duwamish Longhouse (4705 West Marginal Way SW). This interim signal will stop traffic for people crossing West Marginal Way SW. SDOT will plan and design a permanent signal for this same location in as soon as 2022.

Additionally, SDOT will installed a sidewalk in 2021 on the west side of West Marginal Way SW between the Duwamish Longhouse and SW Idaho St to upgrade the dirt path. The new sidewalk will provide direct access for people in wheelchairs and rolling to the Duwamish Longhouse from the parking lots on the east side of West Marginal Way SW and meet Americans with Disabilities standards.  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.


We are committed to Vision Zero goals of reducing motorist speeding, crashing, and fatalities. In 2020, we installed six speed radar signs along West Marginal Way SW to help reduce travel speeds from 40 mph to 30mph. We found that the radar feedback signs reduced vehicle speeds by up to 11% so far. 

Project Timeline 

Winter 2021

  • Engage area businesses, community partners, and neighbors.

  • Outreach to businesses along West Marginal Way via online business survey 

  • Mailer to West Seattle residents 

  • Virtual Open House on February 18, 2021

Spring 2021

  • Compile and analyze feedback

  • Select preferred design option Summer-Fall 2021

  • Project construction and completion

Spring 2022

  • West Seattle High Bridge reopens

  • Begin West Marginal Way SW improvements 

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:

Engagement activities as of May 2021

Project Materials

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