So they may not have metal tracks, but they will be limited to similar turning radii as a subway line just to maintain passenger comfort going at 120 mph. No trains travelling faster than 60 mph are limited in turning radius by mechanical properties.
Wrt. fire suppression: Tesla can state whatever they want, but they will either have to fulfill the demands set forth in NFPA 502 for fire suppression in tunnels, or they will never be allowed to open to the public. Civil engineering is very strict on these things, for a very good reason.
For an underground train, you can have the train platform extend well beyond the actual station building. If you've ever taken the subway/tube in NY or London or similar you know what I mean.
If not, look e.g. at this Google Maps of the Gloucester Road tube stop:
The station building is the small square labeled Gloucester Road tube stop. But the platform extends all the way under the shopping mall (Waitrose's etc) out to the intersection between Cromwell Road and Ashburn Place.
Wrt. fire suppression: Tesla can state whatever they want, but they will either have to fulfill the demands set forth in NFPA 502 for fire suppression in tunnels, or they will never be allowed to open to the public. Civil engineering is very strict on these things, for a very good reason.
For an underground train, you can have the train platform extend well beyond the actual station building. If you've ever taken the subway/tube in NY or London or similar you know what I mean.
If not, look e.g. at this Google Maps of the Gloucester Road tube stop:
https://goo.gl/maps/KQwuSz6RCUE2
The station building is the small square labeled Gloucester Road tube stop. But the platform extends all the way under the shopping mall (Waitrose's etc) out to the intersection between Cromwell Road and Ashburn Place.