"The company can call him at any time, and say 'get to XXX, your train will be there.'"

That another part of the problem with bombcar's concept from the viewpoint of the railroad companies, they'd need a lot more people than you might think so a spare could be close enough to "XXX" to get there without throwing off the Orwellian "Precision Scheduling" of this PSR concept.

The train goes when it's built up to an arbitrary number of cars like 150, not at any set time. Since the system is not even designed for trains that long, it would probably generally back up in any give location if a train was too long delayed in leaving. The companies obviously also wouldn't want to pay for "jets and helicopters" to get a spare to XXX really quickly.