BRIDGE CONSTRUCTION: First new S.R. 520 pontoon en route to floating bridge site

The new S.R. 520 floating bridge will require 77 total pontoons

Bridges News WSDOT August 10, 2012
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The first new State Rte. 520 bridge pontoon is on its way to Lake Washington. Crews began towing the pontoon from Grays Harbor at 9 a.m. Aug. 8 and expect to complete the journey to the Hiram M. Chittenden Locks in Seattle on Saturday, Aug. 11. The pontoon is expected to enter the locks late Saturday night or early Sunday morning.


The tugboat towing the pontoon can be tracked online by searching for vessel “Peter M.” The total distance from Grays Harbor to Shilshole Bay is approximately 260 nautical miles.


Contractor crews working for the Washington State Department of Transportation (WSDOT) built six pontoons in the first construction cycle in Aberdeen. This pontoon is one of three longitudinal pontoons built in the first cycle and measures 360 ft long, 75 ft wide and 29 ft tall and weighs approximately 11,000 tons. The next pontoon is expected to be towed from Aberdeen later this week.


The new S.R. 520 floating bridge will require 77 total pontoons, including 33 being built in Aberdeen and 44 in Tacoma. Twelve pontoons were successfully floated out of casting basins in Tacoma and Aberdeen between July 23 and July 30. WSDOT and contractors Kiewit-General and Kiewit/General/Manson, A Joint Venture continue to inspect and prepare the remaining pontoons for towing.


Project information is available at

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