Friday, July 22, 2016

Heading out: History in motion as old SR 520 floating bridge pontoons set sail

By Haylee Morse-Miller

We're waving a fond farewell to the old SR 520 floating bridge after 53 years of stalwart service.

Vulnerable to wind and waves, the old bridge is now a relic, replaced by a bigger, stronger and safer floating highway. Our next step: take apart and remove the old span from Lake Washington, a process that will continue through the end of the year.

Pontoon E from the old SR 520 bridge floats through the Lake Washington Ship Canal on its way to the locks.

One of the most exciting parts of this process happened Wednesday, July 20, when we towed the first of 31 old floating bridge pontoons from Lake Washington and through the Hiram M. Chittenden Locks in Ballard on its way to new endeavors. Powerful tugboats guided the massive floating piece of concrete along Seattle's waterways.

Like most of the old bridge's 30 other pontoons, Pontoon E is 360 feet long and weighs about 4,725 tons– the equivalent of around 500 adult Orca whales. Towing these enormous boxes of concrete from Lake Washington is a major step in the old floating bridge decommissioning process.

Pontoon E as it passes through the Hiram M. Chittenden Locks in Ballard July 20. The old floating bridge
pontoons are following the same route as the new floating bridge pontoons, but in reverse.

That process is moving along. We removed both the east and west high-rise trusses from Lake Washington in June. In preparation for removing their columns, girders and other concrete superstructures before they are floated out, we also separated four pontoons from the west end (A through D) of the old structure.

What's going to happen to the old bridge?
All 31 massive pontoons make up approximately 75 percent of the old bridge's mass. We will dismantle the old floating bridge's remaining components onsite, then haul them away to concrete-recycling facilities. We'll process most of these materials for reuse on other paving projects throughout the region. So while the old SR 520 bridge will soon be gone, the traveling public will benefit from its recycled components for years to come.

Once traffic shifted onto the new floating bridge, WSDOT' contractor on the project—Kiewit/General/Manson, A Joint Venture (KGM)—took ownership of the old bridge. They now have responsibility for decommissioning the old bridge, including removing the old pontoons from the lake.

We've sold all 31 pontoons to TrueNorth Operations Group, which in the past has resold old pontoons for use as wharfs, docks, storage facilities and artificial reefs. Although we don't know the final destination of the pontoons, we know they will be put to good use wherever they end up in the world.

Want to see the next float out?
If you missed this float out, check out our Facebook Live video report as Pontoon E enters the locks. You can also follow the movement of the 30 other pontoons, which will be floated out of Lake Washington in coming weeks, by following SR 520 on Twitter. If you are interested in watching in person, check out our graphic of suggested viewing locations and join us in commemorating the end of an era.