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Traditionally, [underground train]?s are driven by human drivers, but recently automated trains have been employed, for example in Singapore and London's [Docklands Light Rail]?. |
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Traditionally, [underground train]?s are driven by human drivers, but recently automated trains have been employed, for example in Singapore and London's Docklands Light Railway. |
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The construction of an underground is an expensive project?, often carried out over a number of years. Several modes of tunneling exist. One common method is to place the tracks directly beneath the city street?s, upholding the roads by concrete pillars (parts of the [New York Subway]? system are constructed in this manner). Another usual way is to dig the tunnels beneath previously occupied subterranean space, through native bedrock, and seal the tunnels from leakage of [ground water]? with concrete. |
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The construction of an underground is an expensive project?, often carried out over a number of years. Several modes of tunneling exist. One common method is to place the tracks directly beneath the city street?s, upholding the roads by concrete pillars (parts of the [New York Subway]? system are constructed in this manner, known as Cut-and-cover). Another usual way is to dig the tunnels (often with [Tunnelling shields]?) beneath previously occupied subterranean space, through native bedrock, and seal the tunnels from leakage of [ground water]? with concrete. |
HistoryThe oldest subway tunnel in the world is the Atlantic Avenue Tunnel, built in 1844. Boston has the the oldest subway system in the United States. |
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