I think there's probably some crossover point that makes it more expensive to house people for longer amounts of time with more space required on a train, compa

I think there's probably some crossover point that makes it more expensive to house people for longer amounts of time with more space required on a train, compared to burn a bunch of hydrocarbons to boost them to 800kph and get rid of them as soon as possible. Not sure whether physics make cheaper pricing possible as long as externalities aren't fully factored into the price of fossil fuels (i.e. flying gets more expensive and trains stay the same).