Q I have seen press reports suggesting
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that road tunnels are being considered at Birmingham to link the central areas of the city with the ring roads. Are not road tunnels an obvious solution to the traffic congestion problems of large conurbations, especially London?
ARoad tunnels are likely to be considered
in many built-up areas as the practical difficulties of the surface construction of new trunk, motorways are faced. The general problem of tunnelling was discussed in a paper "Route integration in a built-up environment" by Mr. J. S Moulder, of the highways and transportation department, Greater London Council, at the recent Transportation Engineering Conference. Mr. Moulder revealed that in London tunnels of as much as 62ft internal diameter had been considered. These would provide upper and lower roadways each with 4 X 10ft wide lanes, with 16ft 6in. headroom. Unfortunately, there are considerable technical problems in building such large diameter tunnels—the largest so far driven through the London clay are of 35ft diameter.
Tunnels of 45ft diameter are claimed to be about the same in construction costs as the 62ft diameter tunnels. The 45ft tunnel would permit two "decks"—the top one, for light vehicles, having 12ft 6in, headroom and with two lanes and hard shoulders. The lower road surface would also have two lanes with hard shoulders but would provide 16ft Gin, headroom and be suitable for all classes of vehicles.
As an alternative to the large diameter single-tunnel idea a number of parallel bored tunnels of 40ft diameter, each providing 2 X 12ft lanes plus 8ft hard shoulders is mooted. As each tunnel needs to be separated by roughly its own diameter there are serious problems where the tunnels emerge at the surface. This would involve a cutting some 350ft wide and at least 60ft deep, narrowing to about 134ft over a distance of some 1,150ft.
Although tunnels would provide an attractive solution to long-distance goods vehicles it is thought that local bus operations would not be economically practicable owing to the very high cost of providing loading and discharging points underground.