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SR 520 Bridge Replacement and HOV Program - Design documents

The designs for SR 520 improvements between I-5 and I-405 have undergone many iterations of planning, analysis and stakeholder involvement. This page contains documents that informed the design of the individual projects that make up the SR 520 Bridge Replacement and HOV Program. The documents include community design details, technical analyses, and legislation directing WSDOT to complete these design processes. 

This SR 520 "Rest of the West" webpage contains a listing of key design processes specific to SR 520 reconstruction between Lake Washington and I-5.

Portage Bay Bridge and Roanoke Lid Project design outreach

January 2020 | Summary of 2019 community and stakeholder engagement (pdf 2 mb)

January 2020 | Public comment appendices (pdf 3.2 mb)

SR 520/I-5 Express Lanes Connection Project

October 2019 |  NEPA/SEPA Environmental Reevaluation: I-5 Design Refinements (pdf 398 kb)

2014-2016 West Side Design Refinements

February 2016 | Final concept design report 

2015 Portage Bay Bridge Area Crime Prevention Through Environmental Design

August 2015  | Portage Bay Bridge CPTED final report (pdf 19 mb) 

2011-2012 Seattle Community Design Process

Dec. 20, 2012 | Seattle Community Design Process final report (pdf 31 mb)

Final report broken down in sections

Report in 8.5 x 11 letter format

Public comment summaries

Sept. 14, 2012 | SCDP draft design report

Dec. 2011 | SCDP progress update

Seattle Community Design Process - 2011 Progress Update (pdf 1.3 mb)

Public comment summaries

2011 Record of Decision

  • In August 2011, the Federal Highway Administration published the Record of Decision, which described the project’s course of action and specific mitigation measures. The 2011 Record of Decision can be viewed on the Environmental Documents webpage within the Resource Library.

2011 - Final EIS Preferred Alternative

  • In January 2011, we published the final EIS, which evaluated the "Preferred Alternative" design and included a response to comments received on both the draft and supplemental draft EIS documents. The final EIS Preferred Alternative document can be viewed on the Environmental Documents page within the Resource Library.

2010 – ESSB 6392 Workgroup Design Refinements and Transit Connections

Final report (pdf 4 mb)

ESSB 6392 Workgroup Meeting materials

Dec. 13, 2010 - Seattle City Council presentation materials

Dec. 1, 2010 - ESSB 6392 Workgroup meeting

Sept. 13, 2010 - Seattle City Council presentation materials

Sept. 9, 2010 - ESSB 6392 Workgroup meeting #3 materials

Aug. 19, 2010 - ESSB 6392 Workgroup meeting #2 materials

ESSB 6392 Workgroup meeting #2 materials

Aug. 3, 2010 - Seattle City Council presentation materials

July 22, 2010 - ESSB 6392 Workgroup meeting #1 materials

July 19, 2010

2008-2011 – Miscellaneous design documents

2007-2008 Mediation and ESSB 6099

December 2008 | Westside Project Impact Plan (pdf 6.5 mb)

March 2008 | Proposal K - Tunnels at East Montlake and the Arboretum Conceptual Design and Cost Estimate

April 2006 – I-5 to Floating Bridge Tunnel Concept Review

Transportation reports

Catastrophic Failure Plan

Legislation related to the SR 520 corridor

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