- Undersea tunnel
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). There are many reasons for building an undersea tunnel over a bridge or a ferry link.Advantages of an undersea tunnel
Over Bridges
One such advantage would be that a tunnel would still allow shipping to pass, as a low bridge would not do this (the public may feel a high bridge would be unsightly). Also, a low bridge would need to be an opening or swing bridge to allow shipping to pass and this can cause congestion on the traffic that would pass over the bridge. Tunnels also do not need such huge access ramps to gain the high needed to pass over the expanse of water. Although they may still need to descend deep underground, the tunnel would be able to start inland, without causing too much damage to the area above the tunnel's path.
Bridges may also be closed during periods of high winds and this can also affect the traffic able to use the connection.
Tunnelling 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.
The most obvious advantage, is of course the fact that bridges cannot be used over very large expanses of water, such as the
English Channel .Over 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 (75-90 minutes for Ferry [See: http://www.poferries.com/tourist/content/pages/template/routes_dover_-_calais_timetable_timetable_DOCA.htm] and 21 minutes on theEurostar [See:Eurostar ] ).Disadvantages of an undersea tunnel
Over Bridges
Tunnels require far higher costs of security and construction than bridges. This may mean that over short distances bridges may be constructed rather than tunnels (for example
Dartford Crossing ). As stated above, bridges may not allow shipping to pass, so solutions such as theOresund Bridge have been constructed.Over Ferry Links
As with Bridges, ferry links are far cheaper to construct and operate than tunnels.
List of a few prominent undersea tunnels
*
Sydney Harbour Tunnel
*Seikan Tunnel
*Cross-Harbour Tunnel
*Channel Tunnel
*Eiksundtunnelen world's deepest undersea road tunnelReferences
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