Comment by numpad0

Metro style trains all have it. It's just continental long distance systems that are sometimes lax about those things.

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.