Undersea tunnel

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An undersea tunnel is a tunnel which is partly or wholly constructed under the sea or an estuary. They are often used where building a bridge or operating a ferry link is unviable, or to provide competition or relief for existing bridges or ferry links.[1] While short tunnels are often road tunnels which may admit motorized traffic, unmotorized traffic or both, concerns with ventilation lead to the longest tunnels (such as the Channel Tunnel or the Seikan Tunnel) being electrified rail tunnels.


Compared with bridgesEdit

One such advantage would be that a tunnel would still allow shipping to pass. A low bridge would need an opening or swing bridge to allow shipping to pass, which can cause traffic congestion. Conversely, a higher bridge that does allow shipping may be unsightly and opposed by the public. Higher bridges can also be more expensive than lower ones. Bridges can also be closed due to harsh weather such as high winds.

Tunneling makes excavated soil available that can be used to create new land (see land reclamation). This was done with the rock excavated for the Channel Tunnel, which was used to create Samphire Hoe.

Compared with ferry linksEdit

A map of assessed Helsinki–Tallinn Tunnel through the Gulf of Finland as part of the Rail Baltica project

As with bridges, albeit with more chance, ferry links will also be closed during adverse weather. Strong winds or the tidal limits may also affect the workings of a ferry crossing. Travelling through a tunnel is significantly quicker than travelling using a ferry link, shown by the times for travelling through the Channel Tunnel (75–90 minutes for Ferry[2] and 21 minutes on the Eurostar). Ferries offer much lower frequency and capacity[citation needed] and travel times tend to be longer with a ferry than a tunnel. Ferries also usually use fossil fuels emitting greenhouse gases in the process while most railway tunnels are electrified. In the Baltic Sea, one of the busiest areas for passenger ferries in the world, sea ice is a problem, causing seasonal disruption or requiring expensive ice-breaking ships. In the Øresund region the construction of the bridge-tunnel has been cited as enhancing regional integration and giving an economic boom not possible with the previous ferry links. Similar arguments are used by proponents of the Helsinki-Tallinn tunnel in the Talsinki region. There are various issues with the safety of both tunnels and ferries, in the case of tunnels, fire is a particular hazard with several fires having broken out in the Channel Tunnel. On the other hand, the free surface effect is a significant safety risk for RORO ferries as seen in the sinking of MS Estonia. Tunnels which exclude dangerous, combustible freights and the fuel carried aboard motorcars can significantly reduce fire risk.


Compared with bridgesEdit

Tunnels require far higher costs of security and construction than bridges.[citation needed] This may mean that over short distances bridges may be preferred rather than tunnels (for example Dartford Crossing). As stated earlier, bridges may not allow shipping to pass, so solutions such as the Øresund Bridge have been constructed.

Compared with ferry linksEdit

As with bridges, ferry links are far cheaper to construct than tunnels, but not to operate. Also tunnels don't have the flexibility to be deployed over different routes as transport demand changes over time. Without the cost of a new ferry, the route over which a ferry provides transport can easily be changed. However, this flexibility can be a downside for customers who have come to rely on the ferry service only to see it abandoned. Fixed infrastructure such as bridges or tunnels represent a much more concrete commitment to sustained service.

List of notable examplesEdit

Tunnel Place Description Distance Depth (from surface) Constructed in
Thames Tunnel London, England Thought to be the oldest tunnel under a navigable river, crossing the Thames in London 0.4 km 1825–1843
Mersey Railway Tunnel Liverpool, England The oldest underwater rail tunnel in the world, crossing the Mersey in Liverpool 1.21 km 1881–1886
Severn Tunnel Wales – England One of the oldest underwater rail tunnels in the world 7.01 km 1873–1886
Blackwall Tunnel (western) London, England The oldest underwater vehicular tunnel in the world, crossing the Thames in London 1.35 km 1892–1897
Elbe Tunnel (1911) Hamburg, Germany Pioneering underwater pedestrian and vehicular tunnel, crossing the Elbe River in Hamburg 0.426 km 24 m 1907–1911
Holland Tunnel New York – New Jersey, USA The longest continuous underwater vehicular tunnel in the world when first built, crossing the Hudson River between Manhattan and Jersey City 2.6 km 28.3 m 1920–1927
Queensway Tunnel Liverpool, England The longest vehicular tunnel of any type in the world when first built, crossing the River Mersey between Liverpool and Birkenhead 3.24 km 1925–1934
Bankhead Tunnel Mobile, Alabama Carries Hwy. 90 in Mobile, AL. Business District, to Blakely Island. The eastern end has large "flood door" that can be closed to prevent water from the Mobile Bay from flooding the tunnel during hurricanes or tropical storms. Two lanes that only allows cars and pick up trucks now to travel through the tunnel 1.033 km 12.2m 1938–1942
Lincoln Tunnel New York, USA Set of road tunnels built in three stages, crossing the Hudson River between Manhattan and New Jersey 2.4 km average 30 m 1934–1957
George Massey Tunnel Vancouver, Canada The first tunnel in North America to use Immersed Tube technology 0.629 km 23 m 1957-1959
Detroit–Windsor Tunnel Windsor, Canada - Detroit, USA Connect Ontario, Canada to Michigan, USA. under the Detroit River opened on November 3, 1930 1.57 Km 13.7 m 1928-1930
Chesapeake Bay Bridge Tunnel Virginia, USA Connecting Virginia Beach with the Eastern Shore of Virginia 1.6 km (tunnel section) 1960–1964
Transbay Tube San FranciscoOakland, USA Rail tunnel for Bay Area Rapid Transit. Connects Oakland to San Francisco. It is the longest underwater tunnel in North America 5.8 km 41 m 1965–1969
Cross-Harbour Tunnel Hong Kong A busy road tunnel in Hong Kong 1.86 km 1969–1972
Elbe Tunnel (1975) Hamburg, Germany 8-lane road tunnel crossing the Elbe River in Hamburg 3.3 km 1968–1975
Ahmed Hamdi Tunnel Suez, Egypt Passes under Suez Canal connecting the Asian Sinai Peninsula to the town of Suez on the African mainland 1.63 km 1979–1981
Vardø Tunnel Vardo, Norway Connecting the small island community of Vardø in northern Norway to the mainland 2.9 km 88 m 1979–1982
Kanonersky Tunnel Saint-Petersburg, Russia connecting Kanonersky Island to Kirovsky District of Saint-Petersburg through Neva Bay 0.927 km 1970-1983
Flekkerøy Tunnel Flekkerøy, Norway Connecting the island community of Flekkerøy in southern Norway to the mainland 2.3 km 101 m 1986–1989
Seikan Tunnel Seikan, Japan The Seikan Tunnel is the world's longest tunnel with an undersea segment. 53.8 km 340 m 1971–1988
Sydney Harbour Tunnel Sydney, Australia 2.8 km 1988–1992
Channel Tunnel England – France The world's longest undersea portion railway tunnel (37.9 km underwater length) 50.4 km 1988–1994
Hitra Tunnel Trøndelag, Norway The deepest in the world at the time of construction 5.6 km 264 m 1992–1994
Tokyo Bay Aqua-Line Tokyo, Japan The world's 2nd longest undersea portion road tunnel 9.6 km 1988–1997
North Cape Tunnel Magerøya, Norway The tunnel goes under the Magerøysundet strait between the Norwegian mainland to the large island of Magerøya and the North Cape, Norway 6.8 km 212 m 1993–1999
Bømlafjord Tunnel FøynoSveio, Norway The deepest point of the International E-road network. Connects Stord municipality to the Norwegian mainland. 7.8 km 260.4 m 1997–2000
Massachusetts Bay Outfall Boston, USA The outfall for the Deer Island Treatment Plant. It discharges treated sewage into Massachusetts Bay instead of into the shallower waters of Boston Harbor.[3] Tunnel diameter 24 feet 3 inches (7.39 m) 0.115 km 1992-1998
Eiksund Tunnel Møre og Romsdal, Norway The world's second deepest undersea road tunnel (before 2019 world's deepest) 7.7 km 287 m 2003–2008
Xiang'an Tunnel Xiamen, China 6.05 km 70 m 2005–2010
Busan–Geoje Fixed Link Busan – Geoje, South Korea 3.7 km 48 m 2008–2010
Qingdao Jiaozhou Bay Tunnel HangdaoQingdao, China 7.808 km 84.2 m 2006–2011
Marmaray Istanbul (Bosphorus strait), Turkey Rail tunnel connecting Asia and Europe in Istanbul 1.39 km (Undersea section) 2004–2013
Marina Coastal Expressway Singapore Singapore's first undersea tunnel 5 km 2008–2013
Port of Miami Tunnel Miami, USA 2.1 km 2010–2014
Eurasia Tunnel Istanbul (Bosphorus strait), Turkey Road tunnel connecting Asia and Europe in Istanbul 5.4 km 106 m 2011–2016
Hong Kong–Zhuhai–Macau Bridge Hong Kong – Macau, China 55 km-long sea crossing between Hong Kong, Macau and Zhuhai, China 6.7 km (tunnel section) 2009–2018
The Ryfast Tunnel StavangerRyfylke, Norway The longest and deepest undersea tunnel for cars, from Stavanger to Ryfylke 14.3 km 293 m 2013–2020
Riachuelo Lot 3 Tunnel Buenos Aires, Argentina Outfall tunnel of the Riachuelo System - 2nd world's longest outfall undersea tunnel and 4th world's longest undersea tunnel excavated with TBM 12 km 48 m 2017–2019
Tuen Mun–Chek Lap Kok Link Hong Kong Sea crossing between Tung Chung and Tuen Mun, Hong Kong 5 km (tunnel section) 2011–2020
Eysturoyartunnilin Faroe Islands Sea crossing between Hvítanes, Strendur and Saltnes, under the Tangafjørður strait. Includes an underwater roundabout.[4][5] 11.24 km (overall length)[6] 187 m[7] 2017–2020
Musaimeer Outfall Tunnel Doha, Qatar Diameter - 3.7 m. 10.2 km 40 m 2017-2021
Haicang Tunnel Xiamen, China 6.28 km 73.6 m 2016–2021




See alsoEdit


  1. ^ Sullivan, Walter. Progress In Technology Revives Interest In Great Tunnels, New York Times, June 24, 1986. Retrieved 15 August 2010.
  2. ^ Dover–Calais Ferry Times, poferries.com website.
  3. ^ "The Massachusetts Bay Outfall". Massachusetts Water Resources Authority. Retrieved 29 March 2021.
  4. ^ "Eysturoyartunnilin verður liðugur í 2019". sjovarkommuna.fo. Archived from the original on June 13, 2018.
  5. ^ "Faroe Islands: Inside the undersea tunnel network". BBC News. 4 December 2020. Retrieved 4 January 2021.
  6. ^ "The Eysturoy tunnel". Eystur- og Sandoyatunlar.
  7. ^ "Eysturoy tunnel built by NCC opened in Faroe Islands". NCC. 19 December 2020.
  8. ^ "Undersea Road Tunnel Salamina island - Perama". ec.europa.eu. Retrieved 2020-05-13.
  9. ^ Καραγιάννης, Νίκος (2020-05-12). "Design for Salamina island undersea road tunnel, finalized". Ypodomes.com (in Greek). Retrieved 2020-05-13.
  10. ^ a b "India to build sea bridge, tunnel to connect Sri Lanka at a cost of Rs 24,000 crore". economictimes.indiatimes.com.
  11. ^ "我市全国人大代表返连努力创造属于新时代的光辉业绩_大连新闻_时政经济_大连天健网". dalian.runsky.com. Archived from the original on July 28, 2018.