With the moniker of world’s longest floating bridge hovering around nearly every word written and spoken about the new State Route 520 bridge in Seattle, bridge owner Washington State Dept of Transportation has grown accustomed to the superlatives used when describing its now 1-year-old construction project.
The bridge earned intense coverage from Engineering News-Record magazine’s print pages, this very blog and even ENR’s prestigious 25 Newsmakers award. And on the bridge’s first birthday on April 25, it garnered one more accolade, grabbing the 2017 Grand Conceptor Award from the American Council of Engineering Companies.
“This is an incredible honor for a remarkable project,” Julie Meredith, administrator of the SR 520 Bridge Replacement and HOV Program for WSDOT, said in a statement. “An amazing, collaborative group of people deserve credit for this.”
She made special note of HDR, the general engineering consultant on the reconstruction program; Kiewit/General/Manson, the new floating bridge’s design-builder team; 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, which opened in 1963, measured 130 feet shorter. That span has since been removed from the lake.
“This is one of the great engineering feats or our time,” said Washington state 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. The new floating bridge went bigger than the old in terms of quantity, size and strength of the concrete pontoons meant to withstand the windstorms and waves. The new bridge also elevated over the pontoons 20 ft for an ease of maintenance and so that high waves wouldn’t close the bridge. With the addition of bus and carpool lanes, a cross-lake bicycle-pedestrian path and the opportunity for a light rail retrofit, the new bridge includes more transportation options for commuters between Seattle and points east.
When reconstruction of the entire SR 520 corridor completes, 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 half an hour, according to WSDOT officials.
Follow Tim Newcomb on Twitter at @tdnewcomb.