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

Overall project vision – "Nature meets City"

Montlake lid rendering

The SR 520 corridor is a critical regional highway that is being rebuilt to support many modes of travel. The improved corridor in Seattle will:

  • Create infrastructure that embraces Seattle’s unique natural setting and promotes a vibrant urban environment.
  • Support regional and local connectivity and enhance the environment, with a special focus on shoreline habitat and the use of low-carbon materials.
  • Provide a positive experience for all users, including motorists, pedestrians, bicyclists, transit users, recreationists and residents of adjacent neighborhoods.

Key design elements

Below are the four main stages of SR 520 construction ahead between Lake Washington and I-5 - the Rest of the West:

Montlake Project

Key elements:

  • A new, seismically stronger West Approach Bridge South to carry three lanes of eastbound traffic past Montlake Boulevard to the new floating bridge
  • A landscaped, community-connecting highway lid and transit hub, and improved interchange at Montlake Boulevard
  • A bicycle/pedestrian land bridge over SR 520, east of the lid

Timeline: construction planned to begin in early 2019; estimated duration: 4-5 years

SR 520 / I-5 Express Lanes Connection Project

Key elements:

  • A new, reversible transit/HOV connection between SR 520 and Seattle’s South Lake Union neighborhood, via the I-5 express lanes, to provide safer, more reliable bus and carpool travel between the Eastside, South Lake Union and downtown Seattle

Timeline: construction planned to begin in 2020; estimated duration: 3 years

Montlake Cut Bascule Bridge Project

Key elements:

  • A new, second bascule bridge across the Montlake Cut to provide additional capacity and safer north-south travel through the Montlake area

Timeline: WSDOT will conduct additional coordination with community stakeholders and agency partners regarding the scope of the Montlake Cut Bascule Bridge Project.

Portage Bay Bridge and Roanoke Lid Project

Key elements:

  • A seismically stronger Portage Bay Bridge to replace the existing bridge, which is vulnerable to earthquakes
  • A landscaped, community-connecting highway lid at 10th Avenue East and Delmar Drive East
  • A 30-foot-wide bicycle and pedestrian shared-use crossing over I-5

Timeline: construction planned to begin in 2023; estimated duration: 6 years

Additional design resources:

Public engagement

WSDOT has worked since the late 1990s with the city of Seattle, agency partners, stakeholders and the public to develop, analyze and refine SR 520 designs and solutions.

In 2006, the draft environmental impact statement considered three choices for the project: a four-lane highway, a six-lane highway, and a not-building-anything option. Analysis and public feedback led WSDOT to drop the four-lane alternative and study further the no-build and six-lane alternatives. In 2010, following additional public review and feedback, a six-lane "Preferred Alternative" design was endorsed.

The Preferred Alternative went through more rounds of analysis and refinement, most notably the Seattle Community Design Process in 2011-2012. 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.

From 2014 through 2016, a team of design professionals, working in collaboration with the Seattle Design Commission and supported by WSDOT and city staff, recommended design refinements. Check out our final concept design report for more details.

Visit our Montlake Project page to learn about ways to stay engaged as we prepare for construction.