Those physical mechanisms did have advantages, though. The signals on railways would physically interlock so you couldn't accidentally clear two trains to enter the same portion of track. Perhaps the electrical circuits on modern signalling systems have similar interlocks and it isn't all left up to software (at a minimum you wouldn't want to ever let the system go "all green", for example).
That’s still the case. My mom was Wire Chief at a railroad, and when something broke, everything failed safely and ground movement to a halt until she could get the problem fixed.
Failsafe systems are still common where safety or vast expense is at stake.
