INFRASTRUCTURE
Floating bridges link coasts where deep water blocks fixed spans
Modular pontoons carry highways across fjords, lakes, and bays across the floating economy
I-90 Floating Bridge. Photograph by Rachelle Cunningham.
When deep waters or soft seabeds make traditional bridges impossible, engineers build floating bridges instead. These structures rely on large, airtight pontoons anchored in place to support roadways. They create essential links in challenging landscapes—often faster and more cost-effective than tunnels or suspension bridges.
Key engineering highlights include:
Pontoon design: Floating bridges use massive precast concrete pontoons that provide buoyancy and durability. Seattle’s Evergreen Point Floating Bridge uses 77 such pontoons to span Lake Washington. It reached completion in 2016 and remains the longest floating bridge in the world, stretching 7,710 ft.
Anchoring systems: Pontoons are anchored with cables, piles, or gravity systems to withstand currents, winds, and waves.
Historical foundations: Floating bridges aren’t new. The concept stretches back thousands of years, and modern systems evolved to meet new technical standards and environmental conditions.
Floating Bridge Concept. Image by GlobalMaritime.
Notable floating bridges in action today:
Evergreen Point Floating Bridge (SR 520) spans Lake Washington in Seattle—it opened in 2016 with a replacement capacity for future light rail, and a lifespan estimated at 75 years.
Hood Canal Bridge (William A. Bugge Bridge) in Washington State carries State Route 104 across the Hood Canal inlet. At 7,869 ft, it’s the longest floating bridge in a saltwater environment. Opened in 1961, it remains key regional infrastructure.
Bjørnafjorden Floating Bridge in Norway is set to become the world’s longest. Planned to span over 5 km—more than four times longer than Evergreen Point—it’s part of the E39 highway expansion between Bergen and Stavanger. Design includes floating pontoons and a cable-stayed section for ship clearance.
That’s not all: Floating bridges are also being explored for temporary or emergency use. Modular pontoon systems offer rapid assembly for disaster relief or short-term crossings—though limited in scale or load capacity.
Floating bridges are a clever, flexible solution for linking communities across deep or soft-water bodies. By combining robust engineering with adaptable construction, they help keep transportation flowing where conventional bridges can’t.
- TFI
The Floating Institute is all about advancing knowledge of the global floating economy.