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A retractable bridge is a type of movable bridge in which the deck can be rolled or slid backwards to open a gap for crossing traffic, usually a ship on a waterway. This type is sometimes referred to as a thrust bridge.



Retractable bridges date back to medieval times. Due to the large dedicated area required for this type of bridge, this design is not common. A retractable design may be considered when the maximum horizontal clearance is required (for example over a canal).

Several examples exist in New York City, (e.g., Carroll Street Bridge (built 1889) in Brooklynmarker, Borden Avenue Bridge in Queens). A recent example can be found at Queen Alexandra Dock in Cardiffmarker, Walesmarker, where the bridge is jacked upwards before being rolled on wheels. Helix Bridge [168145] at Paddington Basinmarker, Londonmarker is a more unusual example of the type, consisting of a glass shell supported in a helical steel frame, which rotates as it retracts. The Summer Street Bridge over Fort Point Channelmarker in Bostonmarker is another variant type. This bridge is oriented northwest-southeast, with the NW-bound lanes of traffic retracting diagonally to the north, and the SE-bound lanes retracting diagonally to the west.

Many retractable bridges are also floating bridges, such as the Hood Canal Bridgemarker, where a retractable span can be withdrawn between two lines of pontoons in the shape of a "U". A similar arrangement exists on the Evergreen Point Floating Bridgemarker and Lacey V.marker Murrow Memorial Bridgemarker.

Historical examples of designs for retractable bridges include those by Leonardo da Vinci [168146], and Agostino Ramelli. [168147]

See also





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