How Floating Bridges Work

A Global Gathering of Pontoons

Although Washington State is ground zero for the most numerous and biggest floating bridges, it's by no means the only place you'll find them. Countries around the world maintain their own permanent, pontoon-based constructions.

As with the Seattle area, in Georgetown, Guyana, water (in the form of the Demerara River) was making it hard for the city to grow economically. So in 1978, Guyana built the Demerara Harbor bridge to connect communities and allow for more commercial expansion.

At 1.2 miles (2 kilometers) long, it's the fourth-longest pontoon bridge in the world. It supports a two-lane road and incorporates 122 steel pontoons. Like its Washington cousins, this bridge has suffered its share of problems: deterioration due to lack of maintenance, ship collisions and the sinking of sections due to heavy tides.

As in Washington, Norway has its share of water near population centers. That fact helped spawn a need for the Nordhordland Bridge, which has a floating section that's 4,088 feet (1,246 meters) long. There are 10 pontoons under the bridge of varying sizes, which help the deck cross a fjord and connect to a more traditional, cable-stayed bridge.

Not all currently existing bridges are so large or so new. The Dongjin Bridge in China, for example, has been in use since the Song Dynasty, which took place between 960 and 1279. This (400 meter) bridge still uses wooden boats -- about 100 of them -- to provide buoyancy for the wooden plank deck. The boats are secured to each other with chains.

Regardless of their construction or age, floating bridges have been a part of human transportation for centuries. Not only have they conquered many winds and waves, but they've also stood the test of time. And they'll be around for a long time to come, as long as people still need to find their way across deep waters.

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