Marion Street Bridge overview

As part of the Waterfront Seattle Program, the City of Seattle, in cooperation with the Washington State Department of Transportation (WSDOT), will rebuild a portion of the Marion Street Bridge. The rebuild will happen as part of the removal of the Alaskan Way Viaduct and reconstruction of Alaskan Way. 

The bridge provides an essential pedestrian connection between the multimodal ferry terminal at Colman Dock and major destinations in downtown Seattle including employment and retail, a new transit hub on Columbia Street, and Seattle’s waterfront. The bridge is utilized by the majority of the more than 5 million foot passengers who use Colman Dock annually. The replacement of the Marion Street Bridge is funded by WSDOT as part of the Alaskan Way Viaduct Replacement Program.

Replacing the Marion Street Bridge

The Marion Street Bridge is comprised of three segments built between 1950 and 1970, starting with the western segment over Alaskan Way moving east towards Western Avenue. This project will replace the span across Alaskan Way, from Colman Dock to the east side of Alaskan Way. During Seawall construction, this span was replaced with a temporary structure, which must be removed as part of the removal of the viaduct. The segments east of Alaskan Way to Western Avenue will be replaced in a future phase by the City of Seattle. The segment from Western Avenue to 1st Avenue is in good condition and will be retained.

Goals

  • Provide grade separated connection for patrons of the Colman Dock facility that improves dock and street operations as well as pedestrian circulation.
  • Provide cost-effective, durable and context sensitive design that enhances the waterfront as a place for people.
  • Provide for effective pedestrian circulation within the Colman Dock hub between various modes including ferries, regional and local bus transit, Center City streetcar, private bus service, taxis and ride services and private vehicle pick up and drop off.

Technical Criteria

In addition to the above goals, the new Marion Street Bridge needs to meet technical criteria to accommodate pedestrians using bridge and vehicle traffic beneath the bridge and provide a safe and reliable pedestrian route. These criteria include:

  • Minimum width between railings: 16 feet
  • Minimum Alaskan Way Roadway clearance: 20 feet (to accommodate over-height truck loads)
  • Promenade clearance: 14 to 16 feet
  • Railing height: 36 to 42 inches

Design Process

Based on the goals and criteria, three design concepts have been developed. The City intends to advance a final concept, with design complete by 2018.  The City will work closely with WSDOT to ensure the Marion Street Bridge is cost effective, durable and fits with the context of the Colman Dock and the Waterfront. Construction will begin after the Alaskan Way Viaduct is removed, currently anticipated for 2019.

Concept 1

Concept 1 is a cast-in-place concrete structure. Key features include:

  • Cantilevered approaches (to Colman Dock and toward 1st Avenue)
  • Wide, short concrete pedestrian railings
  • Simple and functional concrete design 
  • Shallow bridge depth to maintain a 20’ vertical clearance above Alaskan Way

Benefits of Concept 1 are:

  • Relatively low construction cost
  • Minimal long-term maintenance

Concept 2

Concept 2 is a structure that combines a standard concrete girder bridge and a cable-stayed bridge. Features include:

  • Cable-stay columns (supported by concrete pylons which allow the bridge to be shorter than typical cable-stay bridges)
  • Narrower bridge cross-section
  • Open and transparent cable pedestrian railing

Benefits of Concept 2 include:

  • Minimal maintenance (due to concrete support)
  • Narrower footprint and height that typical cable-stay bridges
  • Minimally interrupted views from the bridge from cable railing

Concept 3

Concept 3 is a steel and concrete Fink Truss Bridge. Key features and benefits of concept 3 are its slender profile and shallow bridge depth. However, these design benefits are also a drawback, and construction costs and maintenance of this bridge design are much higher than concepts 1 and 2. Because of these challenges, the City plans to carry forward concepts 1 and 2 only.

Outreach

In April 2016, the Office of the Waterfront and Washington State Ferries conducted a series of outreach events sharing information on the multimodal ferry terminal at Colman Dock, the Marion Street Bridge and the overall Waterfront Seattle Program. Information shared during these events is available in the Related documents section, below.

Related documents