[dragontamer]

Tracks fail all the time due to natural disasters... or even just wear-and-tear (heat causes expansion / contraction of lines). Or snow covering an area, making the tracks unsafe.

The answer is simple: a 2nd or 3rd track for redundancy. Which is needed for maintenance purposes anyway. And flamethrowers for snowy areas.

From this perspective, the infrastructure to prove a line of track is safe is just "part of the cost" of a modern rail line. And any such failure is fixed as part of the maintenance costs.

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In any case, if you really wanted to stop a train during rush hour or something, I suggest a crowbar on the rail lines. There's easier ways to derail a train, and sabotage is a known problem. Physical security measures are available, camera systems etc. etc.

But a saboteur with a crowbar is roughly the same problem as too much snow on any given track. We definitely have more to worry from Mother Nature rather than our fellow man (at least.. for now).