Exactly my point. Although even fail-safe systems can fail, as I've personally seen a T-intersection where all the lights were green (which was freaky to see a

Exactly my point. Although even fail-safe systems can fail, as I've personally seen a T-intersection where all the lights were green (which was freaky to see and caused a little traffic jam). But your point still stands, as I'm not sure how the lights got in that configuration; it could have been worker error. Computer-controlled systems that can have disastrous real-world consequences almost always have built-in checks to avoid these failure states.