Quote:
Originally Posted by Quixote
A6 is the best, although Metro's proposal should include using Bechtel's proposed construction methodology (only using a larger TBM) and running automated trains.
They should also have an elevated version of A6.
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Nooo.... the single bore is a bad idea. A bigger tunnel bore needs to be much deeper to avoid surface disruption, so any stations will be many stories deep underground. Several minutes to get from the street level down to the platform. Heavy reliance on elevators and escalators, when most transit agencies don't have the resources to keep them in good working order all the time.
Also there are (or should be) no "station boxes" with this construction type. The sole advantage is that station platforms (and crossovers) can be constructed
within the single bore. In theory the tunneling is much more expensive with single bore, but the savings on stations and crossovers outweighs that for a slightly lower cost overall. If Bechtel is planning station boxes, they're doing it wrong! There is a shaft to the side of the tunnel for vertical access, though.