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World’s Longest Floating Bridge: SR 520 Floating Bridge

Interesting Facts about SR-520,World's Longest Floating Bridge.


World's Longest Floating Bridge
Photo By pgsvensk

World’s Longest Floating Bridge

The Evergreen Point Floating Bridge or commonly known as the 520 Bridge stretching from Lake Washington, Seattle to Medina holds the title of the World Longest Floating Bridge. The Bridge, 7,500 feet long actually, should complete its rebuilding process by 2014 increasing its span to 7710. The World Longest Floating Bridge can take you as close as you could while driving over Lake Washington on a six lane, 116-foot wide deck section. The Evergreen Point Floating Bridge is one of the Projects that the Washington State Department of Transportation (WSDOT) is conducting. Because of the age of the bridge and its inability to withstand more than a 20-year storm, it is being replaced with another, more modern floating bridge.

World Longest Floating Bridge: The Pontoons

The World longest floating bride is being built over pontoons, just like temporary bridges or military crossings are built. A pontoon contains over 58 reinforced concrete anchors that will sink into loose materials on the bottom of the water body to hold the pontoons in place. The SR-520 bridge end anchors will be drilled directly into the ground, while keeping the roadway from swaying. A typical pontoon measures 360 feet long, 75 feet wide and 28 feet tall, however only six feet of the World Longest Floating Bridge will be above water.

These pontoons are so big that external vibrators were used to consolidate concrete instead of using internal vibrators. Furthermore, extra-fluid concrete was also used to produce better results while pouring concrete. The project is part of $367 million phase scheduled to be completed by 2012. However, the pontoons will be floated to the project site as part of a separate $586 million contract.

World Longest Floating Bridge: Engineering Design

The SR-520 Bridge, World’s longest floating bridge, has also been elevated 10 feet above the pontoons using concrete pier, providing extra space for utilities and it reduces the vehicles away from splashing water, water that actually gets over Route 520. The World’s longest floating bridge has also been designed to withstand over 90 miles per hour winds, due to a better engineering design by distributing its weight uniformly over a larger area.

Below the bridge you can expect to have a fire protection system, electrical piping, smart transportation communication system, fiber optic wiring, and a flood protection device to alert when pontoons are flooded. The bridge was also designed to accommodate a future light rail system with only minor improvements to the pontoons.

World Longest Floating Bridge: Key Facts

WSDOT will construct a six-lane SR 520 corridor from I-5 in Seattle to SR 202 in Redmond. The lane configuration across the new SR 520 Bridge includes:

  • Two 11-foot general-purpose lanes in each direction.
  • One 12-foot 3+ transit/HOV lane in each direction.
  • One 10-foot outside shoulder in each direction.
  • One 4-foot inside shoulder in each direction.
  • One 2-foot median barrier.
  • A 14-foot bicycle/pedestrian path on the north side.

Other key facts from the World longest floating bridge are:

  • Governor Albert D. Rossellini Bridge is the official name of the bridge.
  • The current floating bridge is 60 feet wide.
  • The floating section of the SR 520 Bridge is 7,497 feet long.
  • The bridge is supported by 33 bridge pontoons.
  • The SR 520 bridge pontoons standard anchor weighs 77 tons.
  • The deepest point in Lake Washington is 214 feet deep.
  • 115,000 vehicles use the SR 520 Bridge to cross Lake Washington on a daily basis.
  • The existing bridge was designed to withstand 50-70 mph winds, while the new bridge will hold up to 92 mph winds.
  • Pre-stressed concrete pontoons were part of the original bridge design, each pontoon measuring approximately 360 feet long, 60 feet wide and 14.9 feet deep.
  • Washington State is the floating bridge capital of the world with the four longest and heaviest floating bridges.
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