SR 520 - I-5 Express Lanes Connection Project

The SR 520 Bridge Replacement and HOV Program is moving forward, in phases, with construction of the remaining improvements to SR 520 in Seattle – what we call the “Rest of the West.” The SR 520/I-5 Express Lanes Connection Project is one of the major stages of the highway's west side reconstruction. This project will create a dedicated, reversible transit and carpool connection between SR 520 and the I-5 express lanes, along with a reversible transit/carpool ramp at the I-5/Mercer Street interchange. This brief video shows how this new connection will work.

Project news

  • Construction is underway on this new, reversible bus and carpool connection between SR 520 and I-5's Mercer Street interchange. You can learn more from this July blog article and video. Missed our July meeting about what to expect during construction? You can watch a recording or view the presentation (PDF 3.97MB).
  • WSDOT announced in May that Walsh Construction submitted the lowest bid for building this design-bid-build project. You can read more about the announcement in this news release. Subcontractors, including small firms owned by minorities, veterans or women, who are interested in potential contract opportunities on this project should contact Ethan Kaufman, Project Manager, Walsh Construction; work: 206-394-7300 / mobile: 206-579-3856; email:
  • The city of Seattle granted WSDOT a project-long nighttime noise variance for the SR 520/I-5 Project so that crews can do some of the work at night to avoid weekday traffic disruptions and enable a safer work zone. Visit the Seattle Services Portal, project number 6733975-NV, for information on the noise variance and to view WSDOT’s application.  Also, you can read this Q&A on our Major Public Projects Construction Noise Variance (PDF 228KB) to learn more.

Needs & Benefits

Seattle has experienced a population and employment boom, especially in the South Lake Union neighborhood. At the same time, the Eastside’s technology-driven cities continue to experience rapid growth. The region’s growth underscores the importance of a safe, reliable transit/HOV link between Seattle and the Eastside via SR 520. This project will extend SR 520’s new transit/HOV system onto the I-5 express lanes, creating a direct bus and carpool connection between SR 520, South Lake Union and downtown Seattle.

The end result

  • A new, reversible transit/HOV ramp between SR 520 and the I-5 express lanes
  • Restriped I-5 express lanes that retain the four existing lanes while adding a reversible transit/HOV lane between the I-5 / SR 520 interchange and Mercer Street
  • A modified, reversible ramp between the I-5 express lanes and Mercer Street

Project benefits

  • Safer, more reliable travel between the Eastside’s growing cities and Seattle’s booming South Lake Union neighborhood from a new, reversible transit/HOV lane connecting SR 520 and Seattle’s I-5 / Mercer Street interchange
  • Earlier-than-planned Eastside / South Lake Union transit service via the reversible I-5 express lanes connection; the connection could open as early as 2023 or 2024 for transit instead of the originally expected opening in 2029
  • A more efficient phasing of SR 520 construction that minimizes contractor overlap in the Montlake area while keeping regional and local traffic moving during construction


  • Summer 2021: start of construction
  • Estimated construction duration: 3 years*

* The reversible transit/HOV lane initially will open only to transit; carpools will use the reversible lane following completion of a new Portage Bay Bridge and Roanoke lid.


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.


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.