SR 520 - Portage Bay Bridge and Roanoke Lid Project

Project overview

We are preparing to move forward, in phases, with construction of the remaining improvements to SR 520 in Seattle – what we call the “Rest of the West.” The Portage Bay Bridge and Roanoke Lid Project is one of the major phases in the SR 520 Bridge Replacement and HOV Program's reconstruction of the highway's west side corridor.

Needs and benefits

The 1960s-era Portage Bay Bridge is nearing the end of its functional life. Supported by hollow concrete columns, the four-lane bridge could fail in a severe earthquake. This project will replace the old bridge with a seismically stronger structure. The project also will extend SR 520’s transit/HOV system and cross-lake bicycle and pedestrian trail from Montlake to I-5.

The end result

  • Two new parallel, three-lane bridges across Portage Bay – one for eastbound traffic, the other for westbound traffic
  • Dedicated transit/HOV lanes across Portage Bay between Montlake and I-5
  • Extension from Montlake to I-5 of the regional SR 520 Trail
  • A landscaped Roanoke lid over SR 520, between 10th Avenue East and Delmar Drive East
  • A 30-foot-wide bicycle and pedestrian crossing over I-5
  • A system to capture and filter highway runoff before it enters local waterways

Project benefits

  • Safer travel from replacement of the old, structurally vulnerable Portage Bay Bridge with seismically stronger structures 
  • Improved regional mobility with completion of the final stretch of dedicated transit/HOV lanes, in each direction, between Redmond and I-5
  • Greater transportation options by completing the regional, cross-lake bicycle/pedestrian path along the entire SR 520 corridor, and a new, safer shared-use crossing over I-5
  • A community-connecting highway lid with landscaped open space
  • Improved water quality from a new system for treating SR 520 stormwater runoff
  • Fewer traffic backups thanks to wider highway shoulders that allow disabled vehicles to pull over without blocking traffic

Timeline

  • 2023: begin construction (estimated)
  • 2029: complete construction (estimated)

Project design

Our website’s planning-documents webpage contains extensive information about the Seattle Community Design Process and other project-design initiatives and reports. There will be additional design work for future Rest of the West projects, with more opportunities for public comment. Also, the Seattle Design Commission website contains a November 2019 WSDOT presentation (pdf 18 mb) that provides updated design information on the Portage Bay Bridge and Roanoke Lid Project.  

Conceptual illustration of a new Portage Bay Bridge, looking east, with marinas and boats in the foreground and distance

Conceptual illustration of a new Portage Bay Bridge, looking east toward Montlake.

Conceptual illustration of a new Portage Bay Bridge

Conceptual illustration of a new Portage Bay Bridge, looking southwest.

Conceptual illustration of the roadway on a new Portage Bay Bridge, looking east, with cars moving away and overhead highway signs

Conceptual illustration of the three-lane eastbound roadway on a new Portage Bay Bridge.

conceptual illustration of the bicycle and pedestrian SR 520 Trail on a new Portage Bay Bridge, with a man walking on the trail

Conceptual illustration of the shared-use SR 520 Trail on a new Portage Bay Bridge, looking west.

Conceptual illustration of a rebuilt Bill Dawson Trail as it passes under a reconstructed State Route 520, with bicyclists, dog walkers, joggers and pedestrian using the trail

Conceptual illustration of a rebuilt Bill Dawson Trail, looking south as it passes under SR 520.

conceptual illustration of a new shared-use path as it passes under 10th Avenue East and moves onto a new Roanoke lid over SR 520

Conceptual illustration of a new shared-use trail, looking west, as it passes under 10th Avenue East and moves onto a new Roanoke lid over SR 520.

Conceptual illustration of a new Roanoke lid over SR 520, with Portage Bay and a new Portage Bay Bridge in the distance

Conceptual illustration of a new Roanoke lid over SR 520, with 10th Avenue East in the foreground and a new Portage Bay Bridge in the distance.

Plan view of a new Roanoke lid over SR 520, with letters A, B and C showing the location of planned viewpoints on the lid.

Plan view of a new Roanoke lid over SR 520, with the circled letters indicating the location of public viewpoints (shown below).

Conceptual illustration of a viewpoint on a new Roanoke lid, looking southeast from near the corner of 10th Avenue East and Roanoke Street

Conceptual illustration of a viewpoint on a new Roanoke lid over SR 520, looking northeast from 10th Avenue East

conceptual illustration of a Federal Avenue viewpoint on a new Roanoke lid over SR 520, looking northwest

Plan view of a new bicycle and pedestrian crossing over Interstate 5 along the south side of Roanoke Street, with landscaping and a 14-foot-wide shared-use path

Plan view of a new, landscaped bicycle and pedestrian crossing over I-5 along the south side of East Roanoke Street.

Funding

This project is part of the remaining $1.6 billion in SR 520 improvements from Lake Washington to I-5 – the “Rest of the West.” These improvements are funded by the 2015 Connecting Washington transportation legislation. For more information on SR 520 funding, visit the Budget and Performance page.

Contact

Here are some resources you can use to stay informed about this project:

If your organization is interested in receiving a project briefing or presentation, please contact us.