Undersea tunnel
Encyclopedia
An undersea tunnel is a tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...

 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. There are many reasons for building an undersea tunnel as opposed to the construction of a bridge or establishment of a ferry link.

Compared to 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. 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
Channel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

.
Further information: Tunnel –Choice of tunnels vs. bridges

Compared to ferry links

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
Channel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

 (75–90 minutes for Ferry and 21 minutes on the Eurostar
Eurostar
Eurostar is a high-speed railway service connecting London with Paris and Brussels. All its trains traverse the Channel Tunnel between England and France, owned and operated separately by Eurotunnel....

).

Compared to 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
Dartford Crossing
The Dartford - Thurrock River Crossing, Dartford River Crossing is a major road crossing of the River Thames in England, connecting Dartford in the south to Thurrock in the north, via two road tunnels and the Queen Elizabeth II Bridge. It opened in stages, the west tunnel in 1963, the east tunnel...

). As stated earlier, bridges may not allow shipping to pass, so solutions such as the Oresund Bridge
Oresund Bridge
The Øresund or Öresund Bridge is a combined twin-track railway and dual carriageway bridge-tunnel across the Øresund strait.The bridge connects Sweden and Denmark, and it is the longest road and rail bridge in Europe. The Øresund Bridge also connects two major Metropolitan Areas: those of the...

 have been constructed.

Compared to ferry links

As with bridges, ferry links are far cheaper to construct and operate than tunnels, but are subject to suspension of services due to severe weather and heavy seas.

List of notable examples

  • Sydney Harbour Tunnel
    Sydney Harbour Tunnel
    The Sydney Harbour Tunnel is a twin-tube road tunnel in Sydney, Australia. The tunnel was completed and opened to traffic in August 1992 to provide a second vehicular crossing of Sydney Harbour to alleviate congestion on the Sydney Harbour Bridge....

     (2.8 km)
  • Transbay Tube
    Transbay Tube
    The Transbay Tube is the part of BART which runs under San Francisco Bay in California. The tube is 3.6 miles long; including approaches from the nearest stations , it totals 6 miles...

  • Seikan Tunnel
    Seikan Tunnel
    The Seikan Tunnel is a railway tunnel in Japan, with a long portion under the seabed. Track level is about below seabed and below sea level. It travels beneath the Tsugaru Strait—connecting Aomori Prefecture on the Japanese island of Honshu and the island of Hokkaido—as part of the Kaikyo Line...

    , world's longest undersea railway tunnel (53.9 km), when non-undersea portions of the tunnel are also measured
  • Channel Tunnel
    Channel Tunnel
    The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

    , world's longest undersea portion railway tunnel (37.9 km)
  • Marmaray, connecting Asia and Europe
  • Bømlafjord Tunnel, a road tunnel (7.8 km)
  • Tokyo Bay Aqua-Line
    Tokyo Bay Aqua-Line
    The , also known as the Trans-Tokyo Bay Highway, is a bridge-tunnel combination across Tokyo Bay in Japan.It connects the city of Kawasaki in Kanagawa Prefecture with the city of Kisarazu in Chiba Prefecture, and forms part of National Route 409...

    , world's longest undersea portion road tunnel (9.6 km)
  • Eiksund Tunnel
    Eiksund Tunnel
    The Eiksund tunnel is an undersea tunnel between the municipalities of Ørsta and Ulstein in Møre og Romsdal county, Norway. The Eiksund Bridge joins Hareidlandet island and the village of Eiksund with the nearby island Eika. The Eiksund Tunnel begins at the south end of the bridge and connects...

     (7.7 km), world's deepest undersea road tunnel
  • Cross Harbour Tunnel, Hong Kong, a busy road tunnel
  • New Elbe Tunnel, Hamburg, Germany, 8-lane road tunnel crossing the Elbe river
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK