Train wheels are all solid metal so you can watch out for electrical faults between the left and right rails. You can, and this is in fact how many metro style trains operate, require the ground infra to be responding OK and report no faults in the next part of the rail for the train to enter a new section.
Reading other comments, looks like this Spanish system did have a German system that is more advanced that basic electrical fault based system, it was just switched off because it was broken. That's downright reckless, and it shouldn't be a normal behavior.
They don't advertise you how those things work, because it's useless information for most. Doesn't mean they never had such systems for the past ~150 years.
[–] iggldiggl 11 hours ago
[–] iggldiggl 33 minutes ago
That should have read "how to ensure that the train (driver) follows the directions given by the signalling".
LZB (the "German system that is more advanced that basic electrical fault based system") does 2. and 3., but in its usual mainline implementations still needs a conventional train detection system.
> it was just switched off because it was broken. That's downright reckless, and it shouldn't be a normal behavior.
The Spanish line in question is actually equipped with conventional colour-light signalling (and the corresponding conventional train protection system) as a fall back, which is perfectly safe, too.
The only critical bit (which by the looks of it unfortunately failed here) is managing an unplanned transition between the two, because for reasons of cost, the fallback signalling utilises much longer block sections than the LZB signalling, so if the LZB fails unannouncedly, you can end up with multiple trains (each inside its own dedicated LZB block section) inside the same line-side signalling block section, so restarting the train needs to be safely managed by getting them out of the accidentally shared block section one at a time.