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

Simulated view of the new Montlake lid looking west. 

View an animated video of the project design:
- YouTube
- Streaming WMV
What are the key features of the project design?

What are the project features by area?

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

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 and a planted median.
  • A 1,400-foot-long Montlake lid with 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 capacity for buses, carpools, bicycles and pedestrians.
  • 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 are the key Preferred Alternative features by area?


Note: Click each image to expand as a PDF.

I-5 interchange
Portage Bay Bridge 
Note: Final bridge design aesthetics are still to be determined
Portage Bay Bridge
Montlake interchange  
Montlake interchange
West Approach and Floating Bridge



What will the new west side look like?

Note: Click each image to expand as a PDF.

Sketches of the Montlake vicinity 
Bus stops on the Montlake lid 24th Avenue/Montlake interchange Open space on the Montlake lid
Foster Island Lake Washington Boulevard Portage Bay Bridge

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.