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King Street Station Bridge Seismic Projects

Updated: 4/17/2011

Project/Construction Updates

  • The construction contract for the King Street Station Bridge Seismic Projects has been awarded and the construction work has started.  .

Project Description and Location

The King Street Bridges are located along heavily traveled arterials situated between two culturally diverse Seattle Downtown Neighborhoods, Pioneer Square and the International District, and immediately adjacent to the City’s intermodal terminal, the King Street Station. The seismic retrofit improvements constructed by the King Street Bridges Project will increase the seismic performance of these bridges in order to meet the City’s objective of maintaining service along these key transportation corridors after a design level earthquake.

Collectively referred to as the “King Street Bridges” they are specifically:

  • 2nd Ave Extension S from S Jackson St to 4th Ave S : Bridge supporting 2nd Ave Ext S over the BNSF railroad tracks adjacent to the King Street Station between 4th Ave S and S Jackson St.
  • 4th Ave S from S Jackson St to Airport Way S : Bridge supporting 4th Ave S between S Jackson St and Airport Way S. Adjacent to BNSF railroad tracks on the west and office building on the east. Currently the bottom portion of the bridge is utilized as a parking facility for the Union Station Plaza office buildings.
  • S Jackson St from 4th Ave S to 5th Ave S : Bridge supporting a portion of S Jackson St above the Sound Transit tunnel.
  • Airport Way S from 4th Ave S to 5th Ave S (aka Seattle Boulevard Bridge): Bridge supporting a portion of Airport Way S above the south portal of the Sound Transit tunnel.

Bridge History and Project Objectives

The program objectives are to devise, design and construct seismic retrofits for each project to enhance the existing seismic performance of the structures and thereby improving the probability of the structure of maintaining structural reliability, public safety, and traffic mobility after a seismic event. As part of the final design process, consideration will be given to the following factors:

  • Cost of constructing the seismic retrofits
  • Construction duration
  • Constructability issues
  • Utility coordination
  • Aesthetics
  • Innovation
  • Stakeholder impacts and awareness

All four bridges were constructed in circa 1911, a time when seismic events were acknowledged but not fully understood nor encapsulated in the design codes for bridges. As a result, structures of this age are not designed to perform or withstand earthquakes that bridges are currently designed for these days. In order to enhance the seismic performance of these four bridges and retain use of key transportation corridors after a post-seismic event, an assessment will be made of the bridge’s seismic vulnerability and seismic retrofit measures will be devised, designed and constructed that will adequately address the seismic deficiencies of the individual structures.

Project Schedule

The design was completed at the end of 2011 with construction starting in Spring of 2012; because of the complexity of the project and constraints in schedule requirements, the duration of construction is expected to last approximately two year. Almost all of the work anticipated will be done during the night due to conditions regarding access into the project site. It is expected that minimal disruption will be seen by traffic, bicycles, and or pedestrians. Should any work above ground need to be done traffic will be detoured accordingly.

This project is also coordinating with the continued work associated with rehabilitating the King Street Station and the start of the First Hill Street Car project.


Environmental Considerations

SDOT conducted an environmental review of the King Street Bridge Projects and determined the project will not have significant adverse environmental impacts. A State Environmental Policy Act (SEPA) Determination of Nonsignificance is expected to be issued. The environmental review considered potential impacts related to ground disturbance, air and water quality, plants and wildlife, hazardous materials, land use, transportation, and cultural and historic resources, among other things.

The project is currently being reviewed as a Categorical Exclusion under the National Environmental Policy Act (NEPA) by the Washington State Department of Transportation and the Federal Highway Administration. SDOT expects to receive approval under NEPA early this year.

If you have any questions regarding this process please feel free to contact: Mark Mazzola, SDOT environmental coordinator, at 206-733-9117 or

Public Outreach

We are working closely throughout the project with local government, institutions, community groups and businesses, as well as transportation agencies and nearby neighbors, to gather information and help ease construction impacts.

During construction we plan to continue to provide information about the project to the public and keep neighbors engaged through regular e-mail updates. To join our e-mail list, send an e-mail to

Questions or comments?

Contact the SDOT Project Team:

Kit Loo
Project Manager

Maribel Cruz
Outreach Coordinator

Project Funding

The project is funded by Bridging the Gap , a nine-year levy for transportation maintenance and improvements. The $365 million levy was passed by Seattle voters in November 2006. The goal of the program is to create a strong foundation for Seattle’s transportation future by reducing the infrastructure backlog and investing in major transportation projects. The King Street Bridges Project is currently budgeted to cost approximately $20.5 million.

fhwa_logo.jpgIn addition, SDOT proactively sought and secured additional funding for these four bridges through the Federal Highway Bridge Program (HBP). HBP provides funding for the replacement and rehabilitation of deficient bridges and large preventative maintenance projects.



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