An underwater tunnel is a tunnel which is partly or wholly constructed under the sea or a river. 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 electrifiedrail tunnels.
Various methods are used to construct underwater tunnels, including an immersed tube and a submerged floating tunnel. The immersed tube method involves steel tube segments that are positioned in a trench in the sea floor and joined together. The trench is then covered and the water pumped from the tunnel.[2] Submerged floating tunnels use the law of buoyancy to remain submerged, with the tunnel attached to the sea bed by columns or tethers, or hung from pontoons on the surface.[3]
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.
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[4] 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 or lithium-ion batteries carried aboard motorcars can significantly reduce fire risk.
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 links
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.
It is the first underwater tunnel of Asia, as well as India. The construction of this tunnel was completed in 1931.[5] This tunnel is used for electric power transmission between Kolkata and Howrah.
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[clarification needed] cars and pick up trucks now[clarification needed] to travel through the tunnel
The second of three tunnels under the Kanmon Straits, connecting the islands of Honshu and Kyushu. It was the world's longest undersea road tunnel at the time of its construction and includes a tunnel for pedestrians and cyclists
Passes under Suez Canal connecting the Asian Sinai Peninsula to the town of Suez on the African mainland 7 tunnels (2 rail, 4 road, 1 other) under New Suez Canal
The outfall for the Deer Island Treatment Plant. It discharges treated sewage into Massachusetts Bay instead of into the shallower waters of Boston Harbor.[6] Tunnel diameter 24feet 3inches (7.39m)
Rail tunnel serving as a link between Sjælland and Sprogø.
8 km
80 m
1988-1995
Proposed
Road
Rogfast tunnel in Norway – construction having started in 2018, at 27km length, 392 m depth, it will be the longest road tunnel and deepest undersea tunnel in the world.
Karnaphuli Tunnel or Bangabandhu Sheikh Mujibur Rahman Tunnel in Bangladesh Tunnel is an underwater expressway tunnel in the port city of Chittagong, Bangladesh under the Karnaphuli river.
Strait of Gibraltar Tunnel - linking Gibraltar or the Spanish mainland to the African mainland. If built it would most likely become the deepest tunnel ever built
The Faroe Islands is served by an internal transport system based on roads, ferries, and helicopters. As of the 1970s, the majority of the population centres of the Faroe Islands have been joined to a single road network, connected by bridges and tunnels.
The Great Belt Bridge or Great Belt fixed link is a multi-element fixed link crossing the Great Belt strait between the Danish islands of Zealand and Funen. It consists of a road suspension bridge and a railway tunnel between Zealand and the small island Sprogø in the middle of the Great Belt, and a box-girder bridge for both road and rail traffic between Sprogø and Funen. The total length is 18 kilometres (11 mi).
The Hong Kong–Zhuhai–Macau Bridge (HZMB) is a 55-kilometre (34 mi) bridge–tunnel system consisting of a series of three cable-stayed bridges, an undersea tunnel, and four artificial islands. It is both the longest sea crossing and the longest open-sea fixed link in the world. The HZMB spans the Lingding and Jiuzhou channels, connecting Hong Kong and Macau with Zhuhai— a major city on the Pearl River Delta in China.
Kalsoy is an island in the north-east of the Faroe Islands of Denmark between Eysturoy and Kunoy. The name means man island; by contrast with the parallel island to the east, Kunoy, the name of which means woman island.
A bridge–tunnel is a persistent, unbroken road or rail connection across water that uses a combination of bridges and tunnels, and sometimes causeways, and does not involve intermittent connections such as drawbridges or ferries.
Streymoy is the largest and most populated island of the Faroe Islands. The capital, Tórshavn, is located on its southeast coast. The name means "island of currents". It also refers to the largest region of the country that also includes the islands of Hestur, Koltur and Nólsoy.
An immersed tube is a kind of undersea tunnel composed of segments, constructed elsewhere and floated to the tunnel site to be sunk into place and then linked together. They are commonly used for road and rail crossings of rivers, estuaries and sea channels/harbours. Immersed tubes are often used in conjunction with other forms of tunnel at their end, such as a cut and cover or bored tunnel, which is usually necessary to continue the tunnel from near the water's edge to the entrance (portal) at the land surface.
The Fehmarn Belt fixed link or Fehmarn Belt tunnel is an under-construction immersed tunnel, which will connect the Danish island of Lolland with the German island of Fehmarn, crossing the 18-kilometre-wide (11 mi) Fehmarn Belt in the Baltic Sea.
NCC AB is a Swedish construction company, one of the largest in the Nordic region with annual revenues (2023) of 57 billion SEK and about 12 200 employees.
A submerged floating tunnel (SFT), also known as submerged floating tube bridge (SFTB), suspended tunnel, or Archimedes bridge, is a proposed design for a tunnel that floats in water, supported by its buoyancy.
A fixed link or fixed crossing is a permanent, 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–tunnel combination is commonly used for major fixed links.
There are a number of proposed fixed connections—road or rail, bridge or tunnel—designed to connect the islands of Ireland and Great Britain, connect the island of Great Britain to mainland Europe, as well as to build other connections amongst the smaller islands in the British Islands.
The Busan–Geoje Fixed Link or Geoga Bridge is an 8.2-kilometer (5.1-mi) bridge-tunnel fixed link that connects the South Korean city of Busan to Geoje Island. The route opened on December 13, 2010 and shortens the travelling distance between Geoje Island and Busan by about 60 kilometers (37 mi). The new road has two lanes in each direction and carries National Road 58.
Kolkata Metro Line 2, also known as the East-West Metro and Green Line, is a rapid transit line of the Kolkata Metro in the Indian state of West Bengal. It currently consists of two distinctly operational sections between Salt Lake and Sealdah, and Esplanade and Howrah Maidan by going underneath the Hooghly River, with an eastern extension planned for Teghoria. It will cover a distance of 32.11 km (19.95 mi) and consist of 17 stations from Teghoria (Haldiram) in the east to Howrah Maidan in the west, of which it will consist of 11 elevated and 6 underground stations, and the operational section consists of 6 elevated and 6 underground stations, with a total distance of 22 km (14 mi). It is expected to derive a very high ridership, since it will connect India's two largest commuter railway and long-distance railway terminals, Howrah and Sealdah, along with two of its largest business districts, BBD Bagh and Salt Lake Sector V. At present, more than 100,000 passengers commute through the line every day, and this figure is expected to go up to 1 million after it gets fully completed by 2035. It will also connect the industrial hub of Kolkata, i.e., Howrah and the IT hub of Kolkata, i.e., Salt Lake Sector-V. It connects Line 1 at Esplanade and will eventually connect Lines 3 and 6.
Eysturoyartunnilin is a large undersea road tunnel under the Tangafjørður sound in the Faroe Islands, connecting the island of Streymoy to the island of Eysturoy, meaning east island. It also crosses the southern part of Skálafjørður, and connects the towns of Runavík on the eastern side and Strendur on the western side of the fjord, and includes the world's first undersea roundabout in the middle of the network.
Sandoyartunnilin is an undersea road tunnel in the Faroe Islands. It connects the main island of Streymoy with Sandoy to the south. The length of the tunnel is 10.8 kilometres (6.7 mi) and the estimated cost is 860 million DKK. The tunnel opened for traffic on 21 December 2023, after which the ferry Teistin ceased its route between Gamlarætt on Streymoy and Skopun on Sandoy. The tunnel crosses the Skopunarfjørður and runs from Gamlarætt to Traðardalur in central Sandoy, near the Inni í Dal stadium.
East West Metro Tunnel is a underwater river tunnel of Kolkata Metro in Kolkata, West Bengal. The river tunnel is constructed underneath Hooghly River. It is the biggest underwater river tunnel of India, which is made for metro rail service. The East West Metro Tunnel length is 10.8 km (6.7 mi) and width is 5.5 metres. A 520 m stretch of the tracks goes through a tunnel under the Hooghly River. The roof of the tunnel is about 30 metres from the ground level. The tunnel was completed in 2021. The tunnel is used by East West Metro Line for metro rail service by Kolkata Metro Rail Corporation and it was constructed by Afcons Infrastructure.
The Streymin Bridge, is an important highway bridge in the Faroe Islands. It connects the two biggest and most populous islands of Streymoy to the west and Eysturoy to the east. Crossing the Sundini sound at its narrowest point, it is jokingly referred to as the 'Bridge over the Atlantic', being the only inter-island bridge in the Faroe Islands, and one of the few such bridges in the Atlantic Ocean.
The Underwater Road Tunnel Salamina island - Perama is a planned sub-sea road tunnel in the Attica region of Greece, which will provide a direct road link between the island of Salamis of Islands Regional unit in the Saronic Gulf and the port city of Perama in Piraeus Regional Unit, on the east coast of the Saronic Gulf. In whole, the project includes the construction of an underwater road tunnel about 1 km long, the construction of a new road section from Schistos Avenue to the tunnel's entrance in Perama, as well as two new interchanges connecting the adjacent road network in Salamis and Perama.
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