SR 520 - I-5 to Lake Washington - Rest of the West

Project news

  • We’ve created a new set of webpages, called the SR 520 Construction Corner, to help keep the public informed on what to expect from SR 520's reconstruction and how the work will affect travel in and around the corridor. To get the latest on SR 520 construction, including planned highway closures, we recommend bookmarking the Construction Corner or saving it in your web browser's "favorites" folder.


Now that we’ve completed reconstruction of SR 520’s Eastside corridor, built a new floating bridge on Lake Washington and completed the first of two parallel bridges across Union Bay, we are focused on completing the remaining SR 520 improvements from Lake Washington to I-5. These phased improvements, which we call the "Rest of the West," include:

  • the second of two, parallel west approach bridges.
  • landscaped highway lids in Seattle's Montlake and Roanoke neighborhoods.
  • a new bicycle and pedestrian land bridge over SR 520.
  • a new, reversible bus/carpool connection between SR 520 and Seattle’s South Lake Union area.
  • a new Portage Bay Bridge.
  • a second bascule bridge over the Montlake Cut.

Why is WSDOT pursuing these projects?

SR 520’s 1960s-era bridges are structurally vulnerable and at risk of failure in a severe storm or earthquake. In addition, the highway’s old, four-lane segment is typically at capacity during peak periods. The projects we'll construct, in phases, for the Rest of the West will complete all planned safety and mobility improvements on SR 520 from Lake Washington to I-5.

The end result

  • A new, seismically stronger West Approach Bridge South to carry three lanes of eastbound traffic past Montlake Boulevard to the new floating bridge
  • Community-connecting highway lids in Seattle’s Montlake and Roanoke neighborhoods
  • A new, seismically stronger Portage Bay Bridge
  • A landscaped, 30-foot-wide bicycle and pedestrian crossing over I-5
  • A second bascule bridge across the Montlake Cut
  • A bicycle-pedestrian “land bridge” over SR 520 connecting the Arboretum and points northward, including the University District
  • Mitigation and trail-improvement projects in Seattle parks, natural areas and neighborhoods

Project benefits

  • A safer highway for motorists and transit riders by replacing structurally vulnerable bridges
  • Improved regional mobility by adding dedicated transit/HOV lanes across the entire SR 520 corridor, in both directions, and direct-access ramps to and from a regional transit hub on the Montlake lid
  • Greater transportation options by completing a regional, cross-lake bicycle/pedestrian path along the entire corridor, with connections to local trails on both sides of Lake Washington
  • Safer, more efficient north-south travel through Montlake from a second bascule bridge across the Montlake Cut
  • Quicker, safer travel between the Eastside and Seattle’s South Lake Union neighborhood from a new SR 520 transit/HOV connection via the I-5 express lanes  
  • A healthier environment by creating treatment systems for highway runoff, along with other mitigation project

Timeline for Rest of the West projects

We are constructing the remaining SR 520 improvements in phases between the new floating bridge and I-5. The phased projects are:

Montlake Project

  • Elements: New eastbound bridge over Union Bay, Montlake lid and interchange, bicycle/pedestrian land bridge over the highway
  • Timeline: construction began in summer 2019; estimated duration: 4-5 years

SR 520 / I-5 Express Lanes Connection Project

  • Elements: new, reversible transit/HOV connection between SR 520 and Seattle’s South Lake Union neighborhood, running on the I-5 express lanes
  • Timeline: construction began in summer 2021; estimated duration: 3 years.

Montlake Cut Bascule Bridge Project

  • Elements: second bascule bridge over the Montlake Cut
  • Timeline: WSDOT will conduct additional coordination with community stakeholders and agency partners regarding the scope and timing of this project

Portage Bay Bridge and Roanoke Lid Project

  • Elements: Portage Bay Bridge, Roanoke lid, I-5 bicycle and pedestrian crossing
  • Timeline: construction estimated to begin in 2024; estimated duration: 6 years

Project design

  • Our website’s design documents webpage contains extensive information about the Seattle Community Design Process and other project-design initiatives and reports for the Rest of the West projects.


  • The state Legislature's 2015 Connecting Washington transportation legislation authorized $1.64 billion in funding to complete SR 520 improvements from Lake Washington to I-5. For more information on SR 520 funding, visit the Budget and Performance page.


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.

Thumbnail map of the Montlake area. State Route 520 is highlighted in orange

A thumbnail view of the rest of the west project map for the state route 520 program, showing the western end of 520 outlined for various projects.
Rest of the West timeline
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