> For train control lights we almost don't rely on human operators anywhere. Trains are on tracks. They basically move in one dimension. And the tracks can hav

> For train control lights we almost don't rely on human operators anywhere. Trains are on tracks. They basically move in one dimension. And the tracks can have (near) contact-based sensors along the way where the exact distance is known. (And in the US, there still is human conducting in a lot of the US) That’s a very different problem space than the three dimension, unattached, space that air traffic moves in.