Twin bridges
Encyclopedia
Twin bridges are a set of two bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

s running parallel to each other. A pair of twin bridges is often referred to collectively as a twin-span or dual-span bridge. Bridges of this type are often created by building a new bridge parallel to an existing one in order to increase the traffic capacity of the crossing. While most twin-span bridges consist of two identical bridges, this is not always the case. The two bridges that form the Chesapeake Bay Bridge
Chesapeake Bay Bridge
The Chesapeake Bay Bridge is a major dual-span bridge in the U.S. state of Maryland. Spanning the Chesapeake Bay, it connects the state's rural Eastern Shore region with the more urban Western Shore. The original span opened in 1952 and, at the time, with a length of , it was the world's longest...

, for example, have several differences, most notably in the number of lanes each carries. The longest twin-span bridge is the Lake Pontchartrain Causeway
Lake Pontchartrain Causeway
The Lake Pontchartrain Causeway, or the Causeway, consists of two parallel bridges crossing Lake Pontchartrain in southern Louisiana, United States. The longer of the two bridges is long...

 in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

.

For a bridge owner, twin bridges can improve the maintenance and management of the structures. For motorists, twin bridges can limit the risk that both directions of traffic will be disrupted by an accident.
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