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Photo of world's longest floating bridge in Seattle and Bellevue, Washington.


Geotechnical ingenuity and site-specific anchor design overcome challenges to build world’s longest floating bridge

7,710 feet long

floating span, certified the longest in the world when the bridge opened

89 miles per hour

sustained wind speed it is designed to resist, 32 mph faster than original bridge

74,000 motorists

cross bridge each day, on average


  • The Washington State Department of Transportation (WSDOT) needed a replacement for the Evergreen Point Floating Bridge, a stretch of State Route 520 that spans Lake Washington to connect Seattle with communities to the east.
  • The new bridge needed to handle more traffic, accommodate mass transit, and hold up under high winds, waves, seismic seiches, and other environmental forces.
  • But meeting these goals would be challenging, given the difficulty of testing the very soft site soil under the lake, the extreme weather possible in the Pacific Northwest, and the need to withstand seismic activity.
  • The WSDOT and the design/build contractor, Kiewit, trusted Haley & Aldrich to design anchors for a new floating bridge, given our familiarity with the area’s risk factors and our proven track record of designing for resilience.
  • Collaborating closely with other project partners, we took a site-specific approach to anchor design. We used three different types of anchor tailored to specific conditions along the bridge’s path, an approach that enabled us to match anchor design and materials to the exact soil conditions, water depth, environmental constraints, and navigation requirements of each site.
  • This tailored solution helped deliver a bridge with an expected 75-year life span while also saving the WSDOT money and minimizing environmental impact to the lake during construction.

For more information, contact:

Headshot of male, Gary Horvitz
Garry R. Horvitz

Senior Principal Geotechnical Engineer