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SR 520 Bridge Program: I-5 to Medina Project Design

Conceptual rendering of a multimodal hub on a new Montlake lid in Seattle. 

What are the key features of the project design?

What will the final project look like?
How was the project design developed?

The comment period for the January 2015 draft design report ended on Friday, Feb. 13 but we will continue to accept feedback and questions by:

  • Email:
  • Phone: 206-770-3500
  • Mail: SR 520 Bridge Replacement and HOV Program
    999 3rd Avenue, Suite 2200
    Seattle, WA 98104

January 2015 draft design report

Full draft report - 11 x 17 size

One file (pdf 22.5 mb)

Chapter 1 - Executive Summary (pdf 1.6 mb)
Chapter 2 - Design Progression Overview (pdf 856 kb)
Chapter 3 - West Side Final Concept Design (pdf 16.8 mb)
Chapter 4 - Next Steps (pdf 509 kb)
Chapter 5 - Glossary (pdf 158 kb)
Chapter 6 - Appendix (pdf 12 mb)

Full draft report - 8.5 x 11 size

One file (pdf 17.3 mb)

Chapter 1 - Executive Summary (pdf 1.2 mb)
Chapter 2 - Design Progression Overview (pdf 471 kb)
Chapter 3 - West Side Final Concept Design (pdf 13.5 mb)
Chapter 4 - Next Steps (pdf 220 kb)
Chapter 5 - Glossary (pdf 53 kb)
Chapter 6 - Appendix (pdf 9.1 mb)

View an animated video of the project conceptual design:

Read more about an updated cost estimate for the unfunded project elements in Seattle.

What are the key features of the Preferred Alternative project design?

  • A new six-lane corridor from I-5 to Medina that includes two general-purpose lanes and one transit/HOV lane in each direction.
  • A reversible transit/HOV ramp to the I-5 express lanes; headed from the Eastside to downtown Seattle in the morning and from downtown Seattle to the Eastside in the evening.
  • A six-lane Portage Bay Bridge with a westbound managed shoulder for peak traffic.
  • A Montlake lid with green space and bicycle and pedestrian paths that connect the Arboretum, the Bill Dawson Trail and McCurdy Park.
  • An urban interchange at Montlake Boulevard.
  • A second bascule bridge across the Montlake Cut that provides additional multi-modal capacity.
  • A space between the west approach bridge structures that could accommodate potential future light rail and connect to the University Link light rail station. 
  • A 14-foot-wide bicycle/pedestrian path across Lake Washington that connects local and regional trails to the University of Washington and downtown Seattle. 
  • Environmental improvements, including noise reduction features, stormwater treatment, removal of unused R.H. Thomson ramps to restore park land and habitats, and improvements for fish and wetlands. 
  • Priority for transit trips to destinations throughout the region, including downtown Seattle, the University of Washington, Capitol Hill and the Eastside. 


What will the new west side look like?

Note: Click each image to expand as a PDF.

Sketches of the SR 520 corridor 
SR 520 looking northwest SR 520 looking southwest SR 520 looking southeast New floating bridge


How was the project design developed?

1997-2000 Trans-Lake Washington Study

Evaluated multiple options to cross Lake Washington:
• Four-lane options
• Six-lane options
• Eight-lane options
• Alternative modes 
2000-2004 Trans-Lake Washington Project

Narrowed options to cross Lake Washington:
• Six-lane with high capacity transit options including light rail.
• Eight-lane with high capacity transit options including light rail.
• Established SR 520 as a tolled facility 
August 2006 Draft EIS

Draft EIS published and analyzed three alternatives:
• 4-Lane Alternative 
• 6-Lane Alternative 
   - Pacific Street Interchange option 
   - Second Montlake Bridge option 
   - No Montlake Freeway Transit Stop option 
• 8-Lane Alternative 
December 2006 Gov. Gregoire report: A Path Forward to Action

Identified the 6-Lane Alternative as the state’s preferred alternative 
Spring 2007 Legislature passed ESSB 6099

• Began mediation process
• Endorsed 4+2 configuration (four general-purpose lanes and two transit/HOV lanes)
• Began developing SR 520 High Capacity Transit Plan 
December 2008 Mediation ends
SR 520 High-Capacity Transit Plan completed

Mediation group identified three six-lane design options to analyze in Supplemental Draft EIS:
• Option A with suboptions (pdf 8 mb)
Option K with suboptions (pdf 8 mb) 
Option L with suboptions (pdf 8 mb)

WSDOT, King County Metro and Sound Transit released SR 520 High Capacity Transit Plan which defined bus rapid transit across the corridor 
Spring 2009 Legislature passed ESHB 2211

Authorized tolling on SR 520 and formed the SR 520 Legislative Workgroup 
January 2010 SR 520 Legislative Workgroup
Supplemental Draft EIS

SR 520 Legislative Workgroup recommended a six-lane design option with an interchange at Montlake Boulevard (Option A+)

Supplemental Draft EIS published and analyzed three 6-Lane Alternative design options:
• Option A with suboptions
• Option K with suboptions
• Option L with suboptions 
April 2010 Preferred alternative

State identified preferred alternative design option to be analyzed in the final environmental impact statement.
Summer to Fall 2010 ESSB 6392 process
In spring 2010 the Washington State Legislature passed and Gov. Gregoire signed Engrossed Substitute Senate Bill (ESSB) 6392.

ESSB 6392 directed WSDOT to work with regional agencies to refine components of the SR 520, I-5 to Medina preferred alternative, including design refinements and transit connections, and transit planning and financing.

The bill also directed WSDOT to develop a mitigation plan for the Washington Park Arboretum.

Final reports were submitted to the governor and Legislature at the end of 2010. These reports are available online.
June 2011         Final EIS Preferred Alternative
The June 2011 Final EIS analyzed the direct, indirect, and cumulative effects of the Preferred Alternative compared to the No Build Alternative and the three Supplemental Draft EIS 6-lane design options. WSDOT also incorporated the design refinements made during the ESSB 6392 Workgroup process.
Summer 2011 Record of Decision
In summer 2011, the Federal Highway Administration approved the Final EIS and confirmed that the Preferred Alternative could be considered the project’s Preliminary Concept Design with the federal Record of Decision. While WSDOT had adequate budget to complete Final Design of the SR 520 floating bridge and begin construction in 2012, most corridor elements in Seattle did not have funding to advance design or begin construction.
2011 - 2012 Seattle Community Design Process
This robust and collaborative effort between WSDOT, the city of Seattle, design professionals, and the broader public resulted in a refined corridor vision and conceptual design for unfunded portions of the SR 520 corridor in Seattle. While many well-supported design refinements were endorsed and incorporated into the Preliminary Concept Design, the city asked WSDOT to continue exploring the design of the Portage Bay Bridge, Montlake lid, and non-motorized connectivity through Resolution 31427, which was passed in February of 2013.
2014 West side design refinements
Per ESSB 6001, WSDOT and the city continued exploring design elements not resolved through the 2012 Seattle Community Design Process. A team of design professionals, working in collaboration with the Seattle Design Commission and supported by WSDOT and city staff, recommended design refinements for the Portage Bay Bridge, Montlake lid, and nonmotorized connections.