Saturday, July 25, 2009

New York City's Bridges: Third Avenue Bridge

Actually, this photo is of the 1898 swing bridge that was replaced in 2004. A new swing bridge was floated into place by a barge to replace the center two spans of the existing bridge.

This part of the Harlem River (between Manhattan and the South Bronx) is crossed by a variety of movable bridges, which make an interesting subset of river crossings. Among the various movable bridges are bascule bridges, like giant teeter-totters. There are swing bridges (like the Third Avenue Bridge) that move the channel spans parallel to the waterway. There are lift bridges (like the Triborough Lift Bridge) that are like elevators that raise the channel spans up to the top of towers. There are several less common movable bridge types, including innovative recent designs for footbridges. Most movable bridges require an operator to safely open and close the bridge, a mechanical engineer to maintain the bridge, and some patience on the part of the public every time a ship wants to pass. Therefore, if a bridge carries many vehicles, engineers will try to build it high enough so it doesn't interfere with river traffic. However, this requires long ramps to raise the deck above the tallest vessel. Since the latest Maersk container ships can be 80 meters above the water, that makes keeping bridges out of their way quite a challenge.
Creative Commons License
New York City's Bridges: Third Avenue Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

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