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. 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 bridges
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.
- Further information: Tunnel § Choice of tunnels versus bridges
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 and 21 minutes on the Eurostar). Ferries offer much less frequency and capacity and travel times tend to be longer with a ferry compared to a tunnel. Ferries also usually use fossil fuels emitting greenhouse gases in the process while most railway tunnels are electrified, certainly all railway tunnels above a certain length due to ventilation concerns. In waters like 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 abord motorcars can significantly reduce fire risk.
Compared with bridges
Tunnels require far higher costs of security and construction than bridges. 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.
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 examples
|Tunnel||Place||Description||Distance||Depth (from surface)||Constructed in|
|Thames Tunnel||London, England||The oldest underwater tunnel in the world, 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 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|
|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 Francisco – Oakland, 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 (37.9km 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||Føyno – Sveio, 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|
|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|
|Xiamen 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||Hangdao – Qingdao, 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||Stavanger – Ryfylke, 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 - Third world's longest undersea tunnel excavated with TBM||12 km||48 m||2017–2019|
- Eysturoyartunnilin, Faroe Islands to be opened in 2020. The tunnel will have three entrances connected by an underwater roundabout. The road length from Hvítanes to the roundabout will be 7.5 km, whilst the road length from the roundabout to Strendur and to Saltnes will be 1.7 km and 2.2 km, respectively. This results in an overall length of 11.24 km of sub sea tunnel.
- Rogfast tunnel in Norway – construction having started in 2018, at 27 km length, 392 m depth, it will be the longest road tunnel and deepest undersea tunnel in the world.
- Underwater Road Tunnel Salamina island-Perama - planned road tunnel in Attica, Greece. Currently at the second stage of the tender from which the concessionaire will be selected.
- Bohai Strait tunnel in China between Dalian and Yantai (decided, construction to start 'as soon as possible'.)
- Helsinki to Tallinn Tunnel under the Gulf of Finland (proposed)
- Irish Sea Tunnel (suggested)
- Rio de Janeiro Metro Bay Tunnel (Line 3 – Rio de Janeiro-Niterói) (proposed)
- Fehmarn Belt Fixed Link between Denmark and Germany (decided, construction start 2020)
- East West Metro Tunnel, Kolkata Metro in India (under construction, to be opened in 2021)
- Mumbai–Ahmedabad high-speed rail corridor of India (decided, construction start November 2018)
- Penang Undersea Tunnel in Malaysia – to be opened in 2025
- Sullivan, Walter. Progress In Technology Revives Interest In Great Tunnels, New York Times, June 24, 1986. Retrieved 15 August 2010.
- Dover–Calais Ferry Times, poferries.com website.
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- "The Eysturoy tunnel". Eystur- og Sandoyatunlar.
- "Undersea Road Tunnel Salamina island - Perama". ec.europa.eu. Retrieved 2020-05-13.
- Καραγιάννης, Νίκος (2020-05-12). "Design for Salamina island undersea road tunnel, finalized". Ypodomes.com (in Greek). Retrieved 2020-05-13.
- "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.
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