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Posted to uk.d-i-y
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Lets have green public transport
In article ,
says...
The Natural Philosopher wrote:
John Williamson wrote:
Tunnel sizes
Four times, as doubling the bore diameter increases the bore area by
four times. So, boring a double track tunnel costs twice as much
(roughly) per route mile as two single track tunnels. The tunnel walls
also have to be built stronger, increasing the costs further.
Not necessarily.
Single tunnels have a lot more diameter than the train, but a double
tunnel will be a lot closer to 2 trains.
I don't think that's quite right. All tunnels are made to fit the
loading gauge of the system, but single track tunnels can follow it more
closely than twin track, assuming both tunnels have a circular profile.
It's possible to make tunnels elliptical in cross section, but more
expensive in most ground. In decent rock, you can make the tunnel any
shape you like, of course, but how many cities are built on decent rock?
An advantage of a double track tunnel is that you can use the wasted
space above the loading gauge and below the track level to carry pipes
and cables.
Doesn't the same apply to single track tubes?
The roof of London tube trains closely follows the tunnel roof but the
sides are vertical and the sides of the tunnels are filled with pipes
and cables.
--
Terry
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