SR 520 - Floating Bridge and Landings Project - Complete August 2017


The SR 520 Floating Bridge and Landings project replaced the original, 53-year-old SR 520 floating bridge as the “world’s longest floating bridge.” The new span across Lake Washington opened to traffic in April 2016. To learn about how the bridge was constructed, check out our SR 520 floating bridge booklet (pdf 6.8 mb).

Project timeline

  • August 2011 – Floating bridge and landings contract awarded to Kiewit/General/Manson, a Joint Venture.
  • Late 2011 - Pontoon construction begins in Tacoma.
  • Early 2012 - Anchor construction begins in Kenmore.
  • Spring 2012 - Bridge construction begins on eastern shore of Lake Washington.
  • Spring 2016 - New floating bridge opens to drivers.
  • Early 2017 - Removal of the old floating bridge complete.
  • Summer 2017 – All final, remaining work on the new floating bridge project complete.

How you benefit

Improves safety
After over a half century of use, the old SR 520 floating bridge was showing its age. The bridge's pontoons were vulnerable to windstorms and its hollow support columns were vulnerable to earthquakes. The new floating bridge is designed to withstand a 100-year windstorm, and the bridge’s fixed supports on either end have been designed to modern earthquake standards.

Relieves congestion
The old bridge had only two lanes in each direction, no shoulders and no HOV lanes. The new bridge features two general-purpose lanes and one transit/HOV lane in each direction, and wider, safer shoulders that allow vehicles to pull over in the case of a breakdown.|

Provides multimodal options
The 14-foot-wide bicycle/pedestrian path on the north side of the new bridge connects to regional trails on either side of Lake Washington, creating additional recreation opportunities and commuter options

Adding transit/HOV lanes, shoulders and a bicycle/pedestrian path provides greater reliability and more options to accommodate growth in the region. The new bridge also has the ability to accommodate light rail if the region chooses to fund it in the future.

Protects environment
The new floating bridge is designed to capture and filter roadway runoff, which previously drained undiluted off the old floating bridge and into Lake Washington.

The SR 520 Program has also participated in numerous mitigation projects to protect the natural environment of the greater Lake Washington watershed. Learn more about these projects and other environmental benefits on our SR 520 – Environmental Stewardship page.

Partnerships & cooperation
WSDOT and its contractors worked closely with local, state and federal officials, Native American tribes, regulatory agencies, environmental groups, community organizations, transit agencies and many others during the planning, design and construction of the new SR 520 floating bridge.


The project was funded by a variety of state and federal sources, including SR 520 tolling that began in December 2011. The final cost of the Floating Bridge and Landings Project, including preliminary engineering and right of way, was approximately $848 million.

Visit the SR 520 Budget and Performance page for additional information.

This project had a construction change order of more than $500,000. View all change orders.

Noise from new bridge

After the new SR 520 floating bridge opened to traffic in April 2016, some lakeside residents complained about the noise from vehicles crossing the expansion joints on the highway's east high-rise. In response, WSDOT committed to working with the city of Medina and the expansion joint manufacturer to explore options for reducing the noise. Noise studies by WSDOT and later by a University of Washington team found that noise levels from the new bridge's joints were lower than on the old SR 520 bridge, the I-90 floating bridge and the Tacoma Narrows Bridge. Their conclusion was that quieter, specially grooved pavement on the new bridge made the noise of cars running over the new joints more pronounced.

In a January 2019 report to the Legislature, the UW team recommended additional study, in a lab setting, of potential noise-reducing methods. The state House of Representatives approved $555,000 for the pilot project, but the Legislature's final 2019-2021 transportation budget did not fund the study. 


Contact us
Info line: 206-770-3554
Twitter: @WSDOT_520

SR 520 Bridge Replacement and HOV Program
999 3rd Avenue, Suite 2200
Seattle, WA 98104

Map of SR 520 floating bridge
View larger map

SR 520 floating bridge at night

SR 520 floating bridge
To view more project photos, visit our SR 520 Floating Bridge Flickr Collection