New SR 520 floating bridge named America’s top engineering feat

520 Floating Bridge video and booklet
From WSDOT

Precisely one year after opening to traffic, the new State Route 520 floating bridge on Tuesday, April 25, received one of the country’s highest engineering awards: the 2017 Grand Conceptor Award from the American Council of Engineering Companies (ACEC).

The annual award was presented the Washington State Department of Transportation during ACEC’s conference in Washington, D.C. to honor the nation’s best overall engineering achievement.

“This is an incredible honor for a remarkable project,” said Julie Meredith, Administrator of the SR 520 Bridge Replacement and HOV Program for the Washington State Department of Transportation. “An amazing, collaborative group of people deserve credit for this.”

Meredith made special note of HDR, the general engineering consultant on SR 520 reconstruction program; Kiewit/General/Manson, the new floating bridge’s design-builder; and KPFF, the bridge’s lead design consultant.

The floating bridge was one of 162 projects throughout the world vying for ACEC’s top engineering award. The new bridge opened to traffic on April 25, 2016, and is the longest floating span of highway in the world, at 7,708 feet. Its predecessor on Lake Washington – opened in 1963 – measured 130 feet shorter.

“This is one of the great engineering feats of our time,” said Secretary of Transportation Roger Millar. “The new bridge is an example of how our state is working to build a resilient, world-class, multimodal transportation system that will serve generations to come.”

Lake Washington’s extreme depth and soft lakebed required the construction of a floating bridge rather than a conventional fixed bridge.

Online booklet, page 10

The new floating bridge, supported by more, bigger and stronger pontoons than the old bridge, is designed to withstand much stronger windstorms and waves. Moreover, the new bridge provides greater transportation mobility for the region, with bus/carpool lanes in both directions and a cross-lake bicycle-pedestrian path. Its design also allows it to be retrofitted for light rail if the region pursues that option in the future.

When reconstruction of the entire SR 520 corridor is complete, the bridge and connecting highway will carry about 10 percent more vehicles and 17 percent more people during peak traffic hours, while reducing rush-hour, cross-lake commutes between Seattle and Bellevue by about a half hour.

Recent past winners of ACEC’s Grand Conceptor Award are the San Francisco Air Traffic Control Tower (2016); the San Francisco-Oakland Bay Bridge East Span (2015); Wacker Drive/Congress Parkway Reconstruction (Chicago 2014); Kauffman Center for the Performing Arts, (Kansas City, 2013); Lake Borgne Storm Surge Barrier (New Orleans, 2012); and the Hoover Dam Bypass (2011).

A brief video documentary and online booklet – both posted on the new bridge’s April 25 one-year anniversary – provide more information about the structure’s design and construction. You can also follow the SR 520 project on Twitter.

Steve Peer, WSDOT communications