Undersea tunnel

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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.[1]


Compared with bridges[edit]

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.[citation needed]

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

Compared with ferry links[edit]

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 less frequency and capacity and furthermore travel times tend to be longer with a ferry compared to a tunnel.


Compared with bridges[edit]

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.

Compared with ferry links[edit]

As with bridges, ferry links are far cheaper to construct than tunnels, but not to operate.

List of notable examples[edit]

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.[3]
  • 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.


See also[edit]