An undersea tunnel is a tunnel which is partly or wholly constructed under a body of water. They are often used where building a bridge or operating a ferry link is impossible, or to provide competition or relief for existing bridges or ferry links.
Compared with bridges
One such advantage would be that a tunnel would still allow shipping to pass. A low bridge would need to be 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. Another possible advantage is space: the downward ramp leading to a tunnel leaves a smaller footprint compared to the upward ramps required by most bridges.
Tunneling will generate soil that has been excavated and this can be used to create new land, as was done with the soil of the Channel Tunnel.
- Further information: Tunnel – Choice of tunnels vs. 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 furthermore travel times tend to be longer with a ferry compared to a tunnel.
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.
List of notable examples
|Tunnel||Description||Distance||Depth (from surface)||Lifetime|
|Thames Tunnel||The oldest underwater tunnel in the world.||0.4 km||1825–1843|
|Severn Tunnel||One of the oldest underwater tunnels in the world||3.62 km||1873–1886|
|Chesapeake Bay Bridge Tunnel||connecting Virginia Beach with the Eastern Shore of Virginia||37 km – 23 miles||1960–1964|
|Cross Harbour Tunnel||A busy road tunnel in Hong Kong||1.86 km||1972–Present|
|New Elbe Tunnel||8-lane road tunnel crossing Elbe river in Hamburg Germany||3.3 km||1968–1975|
|Vardø Tunnel||Connecting the small island community of Vardø in northern Norway to the mainland||2.9 km||88 m||1979–1982|
|Seikan Tunnel||World's longest undersea railway tunnel when non-undersea portions of the tunnel are also measured||53.9 km||1971–1988|
|Ahmed Hamdi Tunnel||Passes under Suez Canal connecting the Asian Sinai Peninsula to the town of Suez on the African mainland.||1.63 km||1981|
|Sydney Harbour Tunnel||2.8 km||1988–1992|
|Busan–Geoje Fixed Link||World's deepest immersed road tunnel||8.2 km||48 m||2010–Present|
|Channel Tunnel||World's longest undersea portion railway tunnel||37.9 km||1988–1994|
|Tokyo Bay Aqua-Line||World's longest undersea portion road tunnel||9.6 km||1988–1997|
|Hitra Tunnel||The deepest in the world at the time||5.6 km||264 m||1994–Present|
|North Cape Tunnel||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||1993–1999|
|Bømlafjord Tunnel||A road tunnel||7.8 km||263 m||2000–Present|
|Eiksund Tunnel||World's deepest undersea road tunnel||7.7 km||2008–Present|
|Marmaray||Rail tunnel connecting Asia and Europe in Istanbul||1.4 km||2013–Present|
|Marina Coastal Expressway||Singapore's first undersea tunnel||5 km||2013–Present|
|Port of Miami Tunnel||2.1 km – 1.3 miles||2014–Present|
|Eurasia Tunnel||Road tunnel connecting Asia and Europe in Istanbul||5.4 km||2016–Present|
- Eysturoyartunnilin, Faroe Islands to be opened in 2019. The tunnel will have three entrances connected by an underwater roundabout. link 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 a little over 11 km of sub sea tunnel.
- Ryfylke tunnel – under construction, finished 2019, 14 km length
- Rogfast – decided, construction start 2018, 27 km length, 390 m depth, will be longest road tunnel and deepest undersea tunnel in the world.
- Helsinki to Tallinn Tunnel
- Irish Sea Tunnel
- Rio de Janeiro Metro Bay Tunnel (Line 3 – Rio de Janeiro-Niterói
- Bass strait tunnel
- Fehmarn Belt Fixed Link (decided, construction start 2018
- Mumbai–Ahmedabad high-speed rail corridor of India (Construction to start by November 2018
- 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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