Why are tunnels not straight?

The ambient light level is low in a tunnel. With a straight tunnel, a driver would be dazzled by the brightness of the light at the end of the tunnel, so curves are built so that the light level gradually increases. Also, the tunnel lighting gets brighter as you approach the portal.



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Although this is also seen to a certain extent in bridges, it is not to the extent seen in tunnels. Events such as earthquakes and floods, which are the major causes of collapse of other structures, account for only about 10% to 20% of all tunnel collapses.

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The alignment of a tunnel constructed from two ends and meeting somewhere is the middle is achieved via old fashioned surveying methods. If the tunnel breaks through to the surface, surveying stations are accurately established on the surface of the Earth at each end of the tunnel.

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Underground structures last a significantly longer life time than above-ground structures. Approximately about 50 years for above-ground, over 100 years for tunnels.

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If you're anywhere near as obsessed with subterranean London as we are, you'll be bursting with excitement at the prospect of exploring London's abandoned tube tunnels. These disused stations and platforms spend most of the year in peaceful quiet, but on certain days, tour groups are allowed in to get a look.

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The Kingsway Exchange Tunnels, some 40 meters below Chancery Lane tube station in High Holborn, were built in the 1940s to shelter Londoners from the Blitz bombing campaign during World War II.

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Mole people (also called tunnel people or tunnel dwellers) are homeless people living under large cities in abandoned subway, railroad, flood, sewage tunnels, and heating shafts.

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