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Needs to be train size tunnel - the capital cost is huge and you need to shift thousands of posteriors per hour to pay. And ideally it does freight containers too.

Will need aircraft standard safety engineering for leak detection, power failure, pressurisation on vehicle.
Speed - supersonic and complete vacuum could be stage 2 after 1psi and 600 mph which aerodynamic design easier and standard aircraft pressurisation kit.
And lets build one on land first for a few years testing.