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A pedestrian tunnel going under a road, also called a subway. A boat coming to the end of a canal tunnel. A tunnel is an underground passage. When designed for use by traffic, it may be called an underpass.
It may be for pedestrians and/or cyclists, for general road traffic, for motor vehicles only, for rail traffic, or for a canal. Some tunnels are constructed purely for carrying water (for consumption, for hydroelectric purposes or as sewers), while others carry other services such as telecommunications cables.
Tunnels are dug in various types of materials, from soft clays to hard rocks. Depending on the type of soil, a method of excavation is chosen. When digging soft clays, the New Austrian Tunnelling method or NATM is used. When digging in weak rocks a tunnel boring machine or TBM is used. In hard rocks blasting is usually the fastest method, as in the Norwegian tunnelling method .
Various combinations of these methods are also possible. The central part of a metro network is usually built in tunnels. To allow non-level crossings, some lines are in deeper tunnels than others. At metro stations there are often also pedestrian tunnels to walk from one platform to another.
Ground-level railway stations often have one or more pedestrian tunnels under the railway to enable passengers to reach the platforms without having to walk across the tracks.
In the UK a pedestrian tunnel or other underpass beneath a road is called a "subway".
The Lærdal Tunnel in Norway stretching from LærdalThe municipality Laerdal in the county of Sogn og Fjordane, Norway, has 2,178 inhabitants as of January 1, 2002. See also Laerdal. Municipalities of Norway. to AurlandThe municipality Aurland in the county of Sogn og Fjordane, Norway, has 1,807 inhabitants as of January 1, 2002. Municipalities of Norway. is the world's longest road tunnel at 24.5 km, but the St. Gotthard TunnelGotthard Tunnel in Switzerland is the longest road tunnel in the world. It runs from Goschenen in the north to Airolo in the south, and is just under 17 kilometres in length. It links two Swiss cantons: Uri to the north and Ticino to the south. History Th that opened in Switzerland on September 5September 5 is the 248th day of the year (249th in leap years). There are 117 days remaining. Events 1666 Great Fire of London ended: A large fire in London burns out after three days. 10,000 buildings including St. Paul's Cathedral were destroyed, but on, 19801980 is a leap year starting on Tuesday. Events January-February January 1- April 1 National steel strike in United Kingdom January 1 Changes to the Swedish Act of Succession creates Victoria of Sweden, Crown Princess over her younger brother January 5 He is the world's longest highwayA highway is a major road within a city, or linking several cities together. It includes roads known as interstate highway, freeway, motorway and autobahn, where a full description varies by country. Generally, a highway is a road which has multiple lanes tunnel at 16.32 km (10.14 miles) stretching from GöschenenGochenen is a small Swiss town on the northern end of the St. Gotthard Tunnel. It is in the German-speaking part of Switzerland. to Airolo. By contrast, rail tunnels like the Seikan Tunnel in Japan and the Channel tunnel between England and France both exceed 50 km (30 miles). A new St. Gotthard Rail Tunnel with a length of 57 km (36 mi) is currently under construction.
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