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

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 228 kb) to learn more.

Needs & Benefits

Seattle is experiencing 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 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

Timeline

2020: begin construction* (estimated)
2023: complete construction** (estimated)

* Following passage of I-976, Gov. Inslee directed WSDOT to postpone projects not yet underway. This provides the governor and the Legislature flexibility to determine how to adjust the funding gap in the 2019-21 transportation budget during the upcoming session. Learn more about the delay and related projects. (pdf 256 kb)

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

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.