OLYMPIA, Wash – Washington State Department of Transportation crews move closer to another project milestone as the finishing touches are made to the fourth cycle of Tacoma-built pontoons for the new SR 520 floating bridge. These eight new pontoons are scheduled to be towed out of their casting basin into Commencement Bay over a period of four days. The pontoons will be floated out in pairs – the first two on Dec. 26, the last two on Dec. 30 – and then moored for later towing to Lake Washington.

The eight new supplemental pontoons will help provide stability and flotation when attached to much longer, longitudinal pontoons built in Aberdeen. The bridge’s supplemental pontoons each weigh 2,500 to 2,820 tons and measure 98 feet long, 50 to 60 feet wide, and about 28 feet tall.

Six more SR 520 pontoons wait for high tide in Tacoma
Six more SR 520 supplemental stability pontoons are towed out of their Tacoma casting basin in pairs each evening, as the high tides allow.

In all, 44 Tacoma-built pontoons and 33 pontoons built in Aberdeen will support the world’s longest floating bridge. With these eight newest pontoons, WSDOT so far has completed 46 of the bridge’s 77 pontoons. Thirty of these have already arrived at their final destination on Lake Washington.

Stay tuned for photos once the float-out process is complete, and check out our Pontoon Tracking Web page for the latest details about upcoming pontoon movements as they are made available.