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The Longest Floating Bridge in the World is Now Open!

Over 50,000 people visited the floating bridge at the grand opening.

At 7,710 feet long, the new State Route 520 (SR 520) bridge in Seattle, Washington, is the longest floating bridge in the world. In recognition of this incredible project achievement that involved the support of many design and construction firms, the Washington State Department of Transportation hosted a grand opening celebration for the public on 2 and 3 April.

The celebration kicked off with a 10K run/walk, proceeded by a myriad of interactive activities for visitors to enjoy. There were a variety of educational-based activities that highlighted the science, technology, engineering, and math that was used to design and construct the bridge. Visitors were also invited to participate in a city bike ride to showcase the new bicycle and pedestrian paths.

The event also included a ribbon-cutting ceremony with speeches from Governor Jay Inslee and other key speakers. Governor Inslee remarked: “This is not just the longest floating bridge in the world, this is a monument to the confidence we have in ourselves and in the future of the state of Washington. And it is yet another step forward in that long pattern of steps where we have gone from a past to a bright future.”

In addition to being a supporting donor for the opening celebration, BergerABAM served as colead designer for the design-build replacement project, responsible for design quality assurance, and for retaining wall and eastside site civil, pontoon interfaces, transition spans, Pier 36 (the westernmost pier), the east approach bridge, maintenance of traffic and roadway civil, and maintenance facility and maintenance pier designs.

The replacement bridge features six lanes, including two general-purpose lanes and one high-occupancy-vehicle lane in each direction, and a bicycle and pedestrian path on the north side. It has new detention systems for bridge runoff and pollutants to improve water quality and was also designed for the addition of one lane of high-capacity light rail transit in each direction for potential future development.

The new bridge improves safety as it was built with bigger and stronger pontoons, anchors, and anchor cables; it was designed to resist winds up to 89 miles per hour; and it has a taller roadway deck that prevents high waves from reaching the roadway. The completed floating bridge also significantly reduces travel times between Seattle and several neighborhoods to the east along SR 520 and has added several environmental and recreational enhancements that will bring value to the community for many years to come.