SR 520 Bridge Replacement and HOV Program projects

The SR 520 Bridge Replacement and HOV Program is rebuilding one of the Puget Sound region's busiest highway corridors to improve traffic safety, enhance regional mobility and mass transit, and give the public new and better options for nonmotorized travel.
Program construction, which began in 2011, is being done in phases under separate projects and contracts. Click on the links below to visit our individual project pages and learn more about the reconstruction of SR 520.


I-5 to Lake Washington Project

The 2015 Legislature authorized funding to complete the design and construction of SR 520’s west side improvements in Seattle. These include a new Portage Bay Bridge, a new west approach bridge for eastbound traffic, new highway lids in the Montlake and Roanoke neighborhoods, and extension of a new regional bicycle and pedestrian path from Montlake to I-5.

West Approach Bridge North Project

West Approach Bridge NorthSR 520's existing, four-lane west approach bridge is supported by hollow columns that could fail in a strong earthquake. We are replacing the structure with parallel, three-lane bridges that meet current seismic standards. In August 2017 we opened the new approach's north half, which carries westbound traffic from the new floating bridge to Seattle. The south half, not yet under construction, ultimately will carry eastbound traffic from Seattle to the new floating bridge.

Floating Bridge and Landings Project

The new floating bridgeWe replaced the world's longest floating bridge - a four-lane structure built more than a half century ago - with an even longer, safer, six-lane bridge designed to withstand strong windstorms and waves. The new bridge, which opened April 2016, also has shoulders for disabled vehicles and a separate, 14-foot-wide path for bicyclists, walkers and joggers.

Eastside Transit and HOV Project

New HOV lanes, median transit stops, and direct-access ramps for buses and carpools are among the many improvements we've completed on SR 520's Eastside corridor. This 2.3-mile stretch of rebuilt highway also features the first completed segment of a new, regional cross-lake bicycle and pedestrian path and three community-connecting highway lids.

Pontoon Construction Project

This project built 33 of the new floating bridge's 77 pontoons at a casting basin in Aberdeen, Wash. The final three Aberdeen-built pontoons were completed in March 2015. The 44 other pontoons needed to support the new bridge were built at a casting basin in Tacoma. Construction there wrapped up in late 2014.