Viaducts
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A viaduct is a specific type of
bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...
that consists of a series of arches,
pier A pier is a raised structure that rises above a body of water and usually juts out from its shore, typically supported by piling, piles or column, pillars, and provides above-water access to offshore areas. Frequent pier uses include fishing, b ...
s or
column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member ...
s supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide valley, road, river, or other low-lying
terrain Terrain (), alternatively relief or topographical relief, is the dimension and shape of a given surface of land. In physical geography, terrain is the lay of the land. This is usually expressed in terms of the elevation, slope, and orientati ...
features and obstacles. The term ''viaduct'' is derived from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''via'' meaning "road", and ''ducere'' meaning "to lead". It is a 19th-century derivation from an analogy with
ancient Roman In modern historiography, ancient Rome is the Roman people, Roman civilisation from the founding of Rome, founding of the Italian city of Rome in the 8th century BC to the Fall of the Western Roman Empire, collapse of the Western Roman Em ...
aqueducts. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length.


Over land

The longest viaduct in antiquity may have been the Pont Serme which crossed wide marshes in southern France. At its longest point, it measured 2,679 meters with a width of 22 meters. Viaducts are commonly used in many cities that are railroad hubs, such as Chicago, Birmingham, London and
Manchester Manchester () is a city and the metropolitan borough of Greater Manchester, England. It had an estimated population of in . Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92&nbs ...
. 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 rail traffic. These viaducts provide grade separation and 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. Many viaducts over land connect points of similar height in a landscape, usually by bridging a river valley or other eroded opening in an otherwise flat area. Often such valleys had roads descending either side (with a small bridge over the river, where necessary) that become inadequate for the traffic load, necessitating a viaduct for "through" traffic. Such bridges also lend themselves for use by rail traffic, which requires straighter and flatter routes. Some viaducts have more than one deck, such that one deck has vehicular traffic and another deck carries rail traffic. One example of this is the Prince Edward Viaduct in Toronto, Canada, that carries motor traffic on the top deck as Bloor Street, and metro as the Bloor-Danforth subway line on the lower deck, over the steep Don River
valley A valley is an elongated low area often running between hills or mountains and typically containing a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...
. Others were built to span settled areas, crossing over roads beneath—the reason for many viaducts in London.


Over water

Viaducts over water make use of islands or successive arches. They are often combined with other types of bridges or tunnels to cross navigable waters as viaduct sections, while less expensive to design and build than tunnels or bridges with larger spans, typically lack sufficient horizontal and vertical clearance for large ships. See the Chesapeake Bay Bridge-Tunnel. The
Millau Viaduct The Millau Viaduct (, ) is a multispan cable-stayed bridge completed in 2004 across the Canyon, gorge valley of the Tarn (river), Tarn near (west of) Millau in the Aveyron department in the Occitania (administrative region), Occitanie Region, i ...
is a cable-stayed road-bridge that spans the valley of the river Tarn near
Millau Millau (; ) is a commune in Occitania, France. Located at the confluence of the Tarn and Dourbie rivers, the town is a subprefecture of the Aveyron department. Millau is known for its Viaduct, glove industry and several nearby natural ...
in southern France. It opened in 2004 and is the tallest vehicular bridge in the world, with one pier's summit at 343 metres (1,125 ft). The viaduct Danyang–Kunshan Grand Bridge in China was the longest bridge in the world .


Land use below viaducts

Where a viaduct is built across land rather than water, the space below the arches may be used for businesses such as car parking, vehicle repairs, light industry, bars and nightclubs. In the United Kingdom, many railway lines in urban areas have been constructed on viaducts, and so the infrastructure owner
Network Rail Network Rail Limited is the owner (via its subsidiary Network Rail Infrastructure Limited, which was known as Railtrack plc before 2002) and railway infrastructure manager, infrastructure manager of most of the railway network in Great Britain. ...
has an extensive property portfolio in arches under viaducts. In Berlin the space under the arches of elevated subway lines (
S-Bahn The S-Bahn ( , ), , is a hybrid urban rail, urban–suburban rail system serving a metropolitan region predominantly in German language, German-speaking countries. Some of the larger S-Bahn systems provide service similar to rapid transit syst ...
) is used for several different purposes, including small eateries or bars.


Past and future

Elevated expressways were built in major cities such as
Boston Boston is the capital and most populous city in the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States. The city serves as the cultural and Financial centre, financial center of New England, a region of the Northeas ...
( Central Artery), Los Angeles, San Francisco,
Seoul Seoul, officially Seoul Special Metropolitan City, is the capital city, capital and largest city of South Korea. The broader Seoul Metropolitan Area, encompassing Seoul, Gyeonggi Province and Incheon, emerged as the world's List of cities b ...
, Tokyo and
Toronto Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...
( Gardiner Expressway). Some were demolished because they were unappealing and divided the city. In other cases, viaducts were demolished because they were structurally unsafe, such as the Embarcadero Freeway in San Francisco, which was damaged by an earthquake in 1989. However, in developing nations such as Thailand ( Bang Na Expressway, the world's longest road bridge), India ( Delhi-Gurgaon Expressway), China, Bangladesh, Pakistan, and Nicaragua, elevated expressways have been built and more are under construction to improve traffic flow, particularly as a workaround of land shortage when built atop surface roads. Other uses have been found for some viaducts. In Paris, France, a repurposed rail viaduct provides a garden promenade on top and workspace for artisans below. The garden promenade is called the Coulée verte René-Dumont while the workspaces in the arches below are the Viaduc des Arts. The project was inaugurated in 1993. Manhattan's High Line, inaugurated in 2009, also uses an elevated train line as a linear
urban park An urban park or metropolitan park, also known as a city park, municipal park (North America), public park, public open space, or municipal gardens (United Kingdom, UK), is a park or botanical garden in cities, densely populated suburbia and oth ...
. In Indonesia viaducts are used for railways in
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
and also for highways such as the Jakarta Inner Ring Road. In January 2019, the Alaskan Way Viaduct in Seattle was closed and replaced with a
tunnel A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ve ...
after several decades of use because it was seismically unsafe.


See also

* List of bridge types *
Arch bridge An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its structural load, loads partially into a horizontal thrust restrained by the abutments at either si ...
*
Causeway A causeway is a track, road or railway on the upper point of an embankment across "a low, or wet place, or piece of water". It can be constructed of earth, masonry, wood, or concrete. One of the earliest known wooden causeways is the Sweet T ...
* Flying junction * List of bridges ** Crueize Viaduct ** Glenfinnan Viaduct ** Ribblehead Viaduct


References


External links

* * {{Authority control Bridges by structural type