New 520 floating bridge taller, not just wider

WSDOT announced last week that the next-to-last batch of pontoons for the new SR 520 bridge have been completed in Aberdeen.
   That means 66 of the floating bridge’s 77 pontoons are finished, with 57 of them already anchored in Lake Washington. The new bridge is slated to open to traffic in spring 2016.
   People crossing the current Evergreen Point Bridge see a much different span under construction. Its eastern high-rise affords 70 feet of clearance for boats, 15 feet more than the current high-rise. The new bridge is wider, 116 feet versus 60 feet. It includes outside shoulders 10 feet wide and a 14-foot pedestrian and bike path, while the current bridge has almost no shoulders and no path.
   The inside lane for both eastbound and westbound traffic will be set aside for HOV. New HOV lanes already are in use east of the bridge through west Bellevue.
   What really caught my attention is the height of the new road surface. I expected to see support columns taper to nothing as the eastern high-rise dips to meet the midsection pontoons. Instead, the entire bridge’s midsection will remain about 20 feet above the lake surface, higher than the existing bridge’s midsection that sits just 13 feet above the lake.
   That’s a big deal. If you’ve ever crossed the lake in stiff winds on SR 520, you’ve likely been startled as a huge whitecap slams against the bridge and – SPLAT! – whacks your windshield, momentarily blinding you. You react by taking your foot off the gas, braking, or perhaps unwittingly veering to one side.
   While crossing 520 do you ever fret, “How can this concrete bridge float?” WSDOT says the weight of the water displaced by the concrete pontoons equals the weight of the bridge, including vehicles, and that allows the bridge to float.

by  Jon Osterberg



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