Vacuum trains: a high-speed pipe dream? (BBC Future)

[caraher]

13. these accelerations could be quite modest

4000 km/hr is around 1100 m/s - let's round down to 1000 m/s and take g=10 m/s^2. Then at 1 g it takes 100 seconds - less than 2 minutes - to reach such a speed. I'm not sure what the best choice for a propulsion system would be in that case - you're then talking about accelerating over a distance of tens of km.

I think reaching modern jetliner speeds would be a more reasonable and still-useful goal.

Cabin pressure changes don't have to be an issue at all - I presume you would seal the compartments at whatever pressure you like; making it 1 atmosphere is just a matter of building a sturdy enough compartment.

Laying the tubes could be a real showstopper, though. Magma isn't going to be a congenial environment for this!