Helix Bridge at Paddington Basin in London is a more unusual example of the type, consisting of a glass shell supported in a helical steel frame, which rotates as it retracts.
A recent example can be found at Queen Alexandra Dock in Cardiff, Wales, where the bridge is jacked upwards before being rolled on wheels. Two remaining examples exist in New York City: the Carroll Street Bridge (built 1889) in Brooklyn, and the Borden Avenue Bridge in Queens. A retractable design may be considered when the maximum horizontal clearance is required (for example, over a canal).
Due to the large dedicated area required for this type of bridge, this design is not common. Retractable bridges date back to medieval times.
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