Bridge–tunnel
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A bridge–tunnel is a persistent, unbroken
road A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types of ...
or rail connection across water that uses a combination of
bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
s and tunnels, and sometimes
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 Tra ...
s, and does not involve intermittent connections such as
drawbridge A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveable ...
s or ferries. Bridge–tunnels are a form of
fixed link A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
or
fixed crossing A fixed link or fixed crossing is a persistent, unbroken road or rail connection across water that uses some combination of bridges, tunnels, and causeways and does not involve intermittent connections such as drawbridges or ferries. A bridge–tu ...
which replaces ferry service. Fixed links are often, but not necessarily, intercontinental links between continents or transoceanic links to offshore islands.


Tunnels and bridge–tunnels

For water crossings, a tunnel is generally more costly to construct than a bridge. However, navigational considerations at some locations may limit the use of high bridges or
drawbridge A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveable ...
spans when crossing shipping channels, necessitating the use of a tunnel. Examples of such tunnels include the Downtown Tunnel and Midtown Tunnel under the Elizabeth River between
Norfolk Norfolk () is a ceremonial and non-metropolitan county in East Anglia in England. It borders Lincolnshire to the north-west, Cambridgeshire to the west and south-west, and Suffolk to the south. Its northern and eastern boundaries are the No ...
and
Portsmouth, Virginia Portsmouth is an independent city in southeast Virginia and across the Elizabeth River from Norfolk. As of the 2020 census, the population was 97,915. It is part of the Hampton Roads metropolitan area. The Norfolk Naval Shipyard and Naval M ...
in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, the
George Massey Tunnel The George Massey Tunnel (often referred to as the Massey Tunnel) is a highway traffic tunnel in the Metro Vancouver region of southwestern British Columbia. It is located approximately south of the city centre of Vancouver, British Columbia, ...
in
Greater Vancouver Greater Vancouver, also known as Metro Vancouver, is the metropolitan area with its major urban centre being the city of Vancouver, British Columbia, Canada. The term "Greater Vancouver" is roughly coterminous with the geographic area governed b ...
,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, and the
Cross-Harbour Tunnel The Cross-Harbour Tunnel (abbreviated ''CHT'' or ''XHT'') is the first tunnel in Hong Kong built underwater. It consists of two steel road tunnels each with two lanes constructed using the single shell immersed tube method. It is the earl ...
under
Victoria Harbour Victoria Harbour is a natural landform harbour in Hong Kong separating Hong Kong Island in the south from the Kowloon Peninsula to the north. The harbour's deep, sheltered waters and strategic location on South China Sea were instrumental i ...
between the twin cities of Victoria and
Kowloon Kowloon () is an urban area in Hong Kong comprising the Kowloon Peninsula and New Kowloon. With a population of 2,019,533 and a population density of in 2006, it is the most populous area in Hong Kong, compared with Hong Kong Island and t ...
in
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
. In other instances, when longer distances are involved, a bridge–tunnel may be less costly and easier to ventilate than a single, lengthy tunnel. This situation may occur when more economical
drawbridges A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveab ...
are not allowed for one reason or another. For example, in the U.S. state of
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
, such crossings include the
Hampton Roads Bridge–Tunnel The Hampton Roads Bridge–Tunnel (HRBT) is a -long Hampton Roads crossing for Interstate 64 and U.S. Route 60. It is a four-lane facility comprising bridges, trestles, man-made islands, and tunnels under the main shipping channels for Hampton ...
and the
Monitor–Merrimac Memorial Bridge–Tunnel The Monitor–Merrimac Memorial Bridge–Tunnel (MMMBT) is the 4.6 mile-long (7.4 km) Hampton Roads crossing for Interstate 664 in the southeastern portion of Virginia in the United States. It is a four-lane bridge–tunnel composed of bridges ...
, both of which cross the harbor at
Hampton Roads Hampton Roads is the name of both a body of water in the United States that serves as a wide channel for the James River, James, Nansemond River, Nansemond and Elizabeth River (Virginia), Elizabeth rivers between Old Point Comfort and Sewell's ...
, and the Chesapeake Bay Bridge–Tunnel, a structure (including approach highways) that crosses the mouth of the
Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
with a combination of bridges and tunnels across two widely separated shipping channels, using four artificial islands built in the bay as portals. Tunnels had to be used instead of drawbridges because the waterways they cross are critical to military naval operations ( Naval Station Norfolk is nearby, and Chesapeake Bay provides access to the
Potomac River The Potomac River () drains the Mid-Atlantic United States, flowing from the Potomac Highlands into Chesapeake Bay. It is long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map. Retrieved Augus ...
and thus to
Washington, DC ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan ...
) and could not afford to be blocked off by a bridge collapse in the event of disaster or war. Another example is the Øresund Bridge, connecting
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
and
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...
. It has a bridge, an artificial island in the middle of the
Øresund Øresund or Öresund (, ; da, Øresund ; sv, Öresund ), commonly known in English as the Sound, is a strait which forms the Danish–Swedish border, separating Zealand (Denmark) from Scania (Sweden). The strait has a length of ; its width v ...
strait, and a tunnel nearest to
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...
. A bridge could not be built there for two reasons: height restrictions imposed by adjacent
Copenhagen International Airport Copenhagen Airport, Kastrup ( da, Københavns Lufthavn, Kastrup, ; ) is an international airport serving Copenhagen, Denmark, Zealand, the Øresund Region, and southern Sweden including Scania. It is the second largest airport in the Nordic c ...
(the route's path passes the ends of some of the runways; the minimum practical height for a bridge would have interfered with airplanes using those runways) and the perennial threat of ice (a bridge's columns would have encouraged ice dams which could block the strait). The Tokyo Bay Aqua-Line is a bridge–tunnel combination across
Tokyo Bay is a bay located in the southern Kantō region of Japan, and spans the coasts of Tokyo, Kanagawa Prefecture, and Chiba Prefecture. Tokyo Bay is connected to the Pacific Ocean by the Uraga Channel. The Tokyo Bay region is both the most populous a ...
in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. It connects the city of Kawasaki in
Kanagawa Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Kanagawa Prefecture is the second-most populous prefecture of Japan at 9,221,129 (1 April 2022) and third-densest at . Its geographic area of makes it fifth-smallest. Kana ...
with the city of
Kisarazu is a city located in Chiba Prefecture, Japan. , the city had an estimated population of 136,023 in 63,431 households and a population density of 980 persons per km2. The total area of the city is . Geography Kisarazu is located in the midwest ...
in
Chiba Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Chiba Prefecture has a population of 6,278,060 (1 June 2019) and has a geographic area of . Chiba Prefecture borders Ibaraki Prefecture to the north, Saitama Prefecture to the ...
. With an overall length of , it includes a bridge and tunnel underneath the bay—which is the longest underwater tunnel for cars in the world. Drawbridges were impractical here because Tokyo Bay is too active a sea lane. The longest crossing on the Yangtze River in China is a tunnel-bridge-bridge complex, consisting of the
Shanghai Yangtze River Tunnel The Shanghai Yangtze River Tunnel and Bridge is a bridge–tunnel complex across the south fork of the Yangtze River near the river mouth in Shanghai. The tunnel connects the Pudong District of Shanghai on the south bank of the river with Chang ...
,
Shanghai Yangtze River Bridge The Shanghai Yangtze River Tunnel and Bridge is a bridge–tunnel complex across the south fork of the Yangtze River near the river mouth in Shanghai. The tunnel connects the Pudong District of Shanghai on the south bank of the river with Chan ...
(one of the longest cable-stayed bridges in the world),
Chongming–Qidong Yangtze River Bridge Chongming-Qidong Yangtze River Bridge or the Chongqi Bridge (), also called Chongqi Crossing Project (), is a bridge across the north fork of the Yangtze River, near the river's mouth between Chongming Island of Shanghai and Qidong in Jiangsu Prov ...
and connecting viaducts at the river's mouth in
Shanghai Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...
. This fixed link carries the G40 Shanghai–Xi'an Expressway from the north bank to the south bank via two islands and is about in total length.


See also

*
List of bridge–tunnels List of bridge–tunnels: List See also *Transcontinental railroads have many bridge–tunnels. *Intercontinental and transoceanic fixed links A fixed link or fixed crossing is a persistent, unbroken road or rail connection across water that u ...
* Intercontinental and transoceanic fixed links * bridge and tunnel (disambiguation)


References

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