Expectations of an imminent start on a new north-south rail line across London have been damped, with the former chief executive of Network Rail warning that no work on “Crossrail 2” will happen in the next decade. (FT article)
The route, on a south-west to north-east axis from Chelsea to Hackney, was first proposed as a tube line in 1901 and has popped up regularly ever since. Now Crossrail was also originally intended to relieve the congested Central Line and the northern part of the Circle Line. This could have been satisfied by building another tube line on roughly the present alignment from Paddington to Stratford. In an easterly direction, it might have continued to, perhaps, Woolwich, and at the westerly end, it might have run to Hammersmith, and possibly, eventually, Heathrow.
The London tube uses small 3.5 metre diameter tunnels and electrification by conductor rail. Crossrail, by contrast, is a full-sized railway with overhead electrification, requiring 6 metre tunnels. Thus, almost four times as much material has to be excavated, and costs cannot be less then double the cost of a tube line.
Thus, for the price of Crossrail 1, Londoners could have had both Crossrail 1 and Crossrail 2 for their money. Thus is the money wasted on over-specified infrastructure. How did this happen?
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Although there is a more material to be excavated, that is only one element of the construction costs. There is also the tunnel lining (which isn't quite double), the leasing of the tunnelling equipment (which probably isn't directly proportionally related to the size of the diameter of the tunnel) and of course the rails (which does not change regardless of the diameter of the tunnel).
Conversely, if you have a smaller tunnel size the trains have to be smaller and therefore to carry the same number of passengers the stations have to be longer. This may not seam to be a big problem, however given the largest costs associated with Crossrail is the building of the station boxes lengthen the stations would have likely cost more than it would have saved to build smaller tunnels.
It should also be noted that Crossrail 2 has a "tube" option which was costed at £9.4bn compared to the regional (full sized train) option at £12bn. Which is nowhere near as much as double, it's not even a 1/3 more and even that isn't a fair comparison as the regional option has more tunnelling (length) then the metro option.
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