• RentlarOP
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      7 months ago

      The requirements for a train tunnel are different than for a bus tunnel, which “may” be cheaper depending on what you compare to. Usually a bus tunnel will need to also accommodate diesel and gas(petrol) burning vehicles which increases ventilation requirements significantly. A train tunnel might be electric only or have diesel engines running through it. A train tunnel will need to meet the accepted standard rail vehicle envelope of the region or the isolated rapid transit system, same with road vehicles, but since the latter includes taller trucks, the height clearance would be necessarily higher than buses.

      Single line width rail tunnels are used, but dual lane tunnels are the choice for some new passenger rail projects for the speed of being able to bore them even if it is more expensive.

        • RentlarOP
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          7 months ago

          Kinda. They are about the same speed, comparing the Scarborough Subway single TBM vs. the Eglinton Crosstown are both purpoted to travel 10m to 15m per day. Even if the speed of the smaller TBMs is a bit faster, the design of having one tunnel vs. two tunnels would be different. Costs of tunneling might vary greatly by project, accounting for each locations’ ground conditions and existing infrastructure to navigate around. So I concede that I could be wrong about the price in the general case when comparing 1 big vs. 2 small machines.