Viaduct

Viaduct

Laigh Milton Viaduct in Ayrshire is the oldest surviving railway bridge in Scotland
Ancestor	Trestle bridge, Box girder bridge
Related	None
Descendant	None
Carries	Expressways, highways, streets, railways
Span range	Short (multiple)
Material	reinforced concrete, prestressed concrete, masonry
Movable	No
Design effort	medium
Falsework required	available for use, since viaducts are all composed of low bridges.

A viaduct is a bridge composed of several small spans for crossing a valley, gorge, marshland or forming a flyover. The term viaduct is derived from the Latin via for road and ducere, to lead. The ancient Romans did not use the term; it is a modern derivation from an analogy with aqueduct. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length. Viaducts may span land, water or both.

A viaduct is a bridge composed of several small spans for crossing a valley or a gorge. The term is conventional for a rail flyover as opposed to a flying junction or a rail bridge which crosses one feature. In Romance languages, the word viaduct refers to a bridge which spans only land. A bridge spanning water is called ponte.

The longest viaduct in antiquity may have been the Pont Serme which crossed wide marshes in southern France.

Viaducts are commonly used in many cities that are railroad centers, such as Chicago, Atlanta, Birmingham, London and Manchester. These viaducts cross the large railroad yards that are needed for freight trains there, and also cross the multi-track railroad lines that are needed for heavy railroad traffic. These viaducts keep highway and city street traffic from having to be continually interrupted by the train traffic. Likewise, some viaducts carry railroads over large valleys, or they carry railroads over cities with many cross-streets and avenues.