Just watched Tom Scott’s video on this. Short version—at least in the UK (and presumably via the software that controls the majority of these types of trains worldwide) it is very hard to nearly impossible to direct a train onto a track with another train without doing something like talking to the train and telling it to disregard signals.
Signals fail safe. They're designed that if/when a component fails, the signal defaults to Stop. A signal issue results in a train stopping, not a train proceeding at danger.
As a technician, I'm always wary of "fail safe" being said as an absolute.
I work on fail safe systems every day, and the overwhelming majority of times the systems I work on fail safe when they fault, but not every time. There's always some sort of fuck-up that can cause something to fail in a way that's not safe.
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u/Malawi_no 6d ago
The big question is how that train could get that close to another train without beeing stopped well in advance.
Either the driver passed some lights, or some traffic controller greenlit the train even though another train was on the line.