SR 520 - I-5 to Lake Washington

Project news

  • The 2015 Legislature approved funding for SR 520's planned improvements from I-5 to Lake Washington - the "Rest of the West." These improvements include highway lids in Seattle's Montlake and Roanoke neighborhoods, the south half of a new west approach bridge, a new Portage Bay Bridge, and a second drawbridge over the Montlake Cut. WSDOT is preparing to begin the first phase of construction, known as the Montlake Phase, in late 2018.
  • More than 250 people attended our April 17 open house in Montlake to learn more about the next phase of SR 520 construction in Seattle. Miss the meeting? You'll find all of the open house's informational boards in our Resource Library. Also, we answer many of the questions we heard at the open house in this recent SR 520 blog article.
  • We receive a lot of questions about what's ahead for SR 520 reconstruction in Seattle. Read our latest FAQs (pdf 123kb), updated May 2, to learn the latest.
  • On April 26 we received a noise variance from the city of Seattle for the upcoming Montlake Phase of SR 520 construction. More information on the variance (document #3030792) is available on the city of Seattle's website. You also can read our Q&A (pdf 539 kb) on the variance.


Why is WSDOT pursuing this project?
This project, in phases, will complete all planned safety and mobility improvements on SR 520 from Lake Washington to I-5.

The End Result

  • A safer highway for motorists and transit riders from the replacement of structurally vulnerable bridges.
  • Improved regional mobility from the addition of dedicated HOV lanes across the entire SR 520 corridor, in both directions.
  • Greater transportation options with the completion of a regional, cross-lake bicycle/pedestrian path along the entire corridor.
  • A healthier environment from the creation of treatment systems for highway runoff and other mitigation projects.


Project Benefits

Future improvements to the highway’s western segment in Seattle include:

  • 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 to provide additional capacity and safer north-south travel on Montlake Boulevard.
  • A bicycle-pedestrian “land bridge” over SR 520 connecting the Arboretum and points northward.
  • Related mitigation and trail-improvement projects in Seattle parks, natural areas and communities.


What is the project timeline?

The 2015 Washington Legislature fully funded the remaining improvements to SR 520 between I-5 and the new floating bridge. The upcoming phases of construction, in order, are:

Montlake Phase

  • Elements: West Approach Bridge South, Montlake lid and interchange, and land bridge over the highway
  • Timeline: construction planned to begin in late 2018; estimated duration: 4-5 years

Portage Bay Phase

  • Elements: Portage Bay Bridge, Roanoke lid, and I-5 connections
  • Timeline: construction to begin as early as 2020; estimated duration: Multiple contracts

Montlake Cut Crossing Phase

  • Elements: second bascule bridge over the Montlake Cut
  • Timeline: construction to begin as early as 2024; estimated duration: 3 years

The first two phases are each planned to be delivered as design-build contracts. The type of contract for the final phase will be determined in the future. 

This graphic (pdf, 767 kb) shows the project phasing for the Rest of the West.


Financial Information

  • In the 2015 Connecting Washington transportation legislation, the state Legislature authorized $1.64 billion in funding to complete SR 520 improvements from Lake Washington to I-5 – the “Rest of the West.” For more information on SR 520 funding, visit the Budget and Performance page.


How can I get more information?