#worldslongestfloatingbridge SR 520 World Record measurement

The Evergreen Point Floating Bridge, commonly called the SR520 bridge, is the longest floating bridge in the world.

But not for long.

In April, 2016, the Washington State Department of Transportation will open the new SR520 bridge to traffic. This new bridge will, in theory, take over the title of longest floating bridge in the world.

Derek Cress, a surveyor with WSDOT's Northwest Region, sets up survey equipment to measure the length of the 520 floating bridge.

To find out for sure a team of surveyors from WSDOT met on the bridge on February 12, 2016, to measure the new floating span. They used a mix of high-tech and traditional measuring tools to calculate the distance.

A laser survey device measure the distance between reference points on Pontoons A and W. The distance calculated by the laser measurement is 7681.864 feet.

The floating span consists of giant concrete pontoons, with each end of the floating section connected to fixed approach bridges from the east and west.

To measure the length of the new span, engineers used a laser measuring device carefully placed directly over a bolt on the A and W pontoons to calculate most of the distance. However, since the pontoon edges drop off straight into water, it wasn't possible to use the survey equipment to calculate the full length.

How did engineers tackle this problem? With old-fashioned tape measures!

Engineers measure the distance from the edge of the pontoons to the known point used to position the laser measurement equipment.

With the tape measure and laser distances in-hand all that's left is basic addition!

Engineers note the distance from pontoon edges to known point, and the laser measured distance between Pontoons A and W.
An engineer uses a Windows Phone to verify the calculations.

After crunching the numbers the WSDOT engineering team confirms it: at 7,708.494 feet the new SR 520 floating span will be the new world's longest floating bridge!

Created By
Neil Enns


Neil Enns/Dane Creek Photography

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