[mapt]

I'll re-issue my prediction: an STP hydrogen tunnel with elecromagnetic levitation (my favorite being Inductrack, known for its passive failsafe) and propulsion, and wheels for low speeds, makes a lot more economic sense than an evacuated tunnel. Much less drag, much higher speed of sound.

The other things that any modern engineer would never do that an 1870's railroad technician somewhere built into SOP, like mixed speed segments, frequent braked unbanked turns, single-tracking, and manual signalling / switching and grade crossings, will also be consciously avoided; the FRA regulations are built on making operating under such principles safer. Applying modern real-time at-speed routing to rail is something the PRT guys have been dreaming about for decades - the money and organizational will just hasn't been there to make it happen at a scale sufficient to make it cheap enough to justify.

[throwaway_yy2Di]

Sounds like an insane fire hazard. With large volumes of hydrogen and breathable air in close proximity, otherwise minor failures would be catastrophic.