A floating concrete and steel bridge may seem very strange, sometimes impossible, but there are twenty such bridges around the world, five of them in the US state of Washington, of which four are the longest floating bridges on the planet.
Homer Hadley and Lacey V. Murrow Memorial Bridges on Lake Washington.
Floating bridges, also known as pontoon bridges, are usually temporary structures built of wood in times of emergency, such as in war situations. Wooden floats, and sometimes several boats, must be tied to these bridges so they don’t sink.
Pontoon bridges have been used to great advantage in many battles throughout historyincluding World War II and during the Iran-Iraq War.
The longest permanent floating bridge in the worldEvergreen Point, commonly called “SR 520 Bridge”, is located across Lake Washington, in Seattle. It absorbs traffic from State Route 520 and is 4,750 meters long.
On the other hand, the Lacey V. Murrow Memorial Bridge, the second longest bridge in the worldis found across the same lake a few kilometers south of Evergreen Point, and is 2,020 meters long.
But…why floating bridges? The answer is in the complicated geographic location of Lake Washington. The lake bed is too unstable for conventional bridge supports. And the other option, a suspension bridge, would require towers that would have been too expensive.
The idea of a floating bridge across Lake Washington was first proposed by engineer Homer Hadley in the 1930s. Hadley had worked for a concrete barge design firm during World War I and proposed the idea of connecting barges from end to end of the lake to Lacey V. Murrow, then responsible for the state of the roads.
Hadley’s floating bridge was such a success that the state of Washington adopted the concept for future bridges.
The second bridge to be built, Evergreen Point, the longest in the world today, it was opened in 1963. Finally, and again on Lake Washington, the third bridge was named Homer Hadley in honor of the man who spearheaded the idea of such bridges.
Nowadays, Lake Washington is home to three of the five longest floating bridges in the world.