The trains ride on a track. The tracks have sensors. The sensor positions are known. Now you know where all of the trains are.
GPS satellites could drop out of the sky and you’d still know where the trains are.
Not sure whether this means that the various signalling suppliers are waiting for a customer to take on the technical risk of being the first to deploy UWB CBTC, or that there were costs or disadvantages that make it unattractive.
What?
There’s one as far apart as you put them. The precision is what you make it.
I’m not entirely sure what you are trying to argue. Your original comment said you can’t know where trains are on underground subways because GPS doesn’t work underground, but that’s not the technology they use anyways, so it doesn’t make sense to reference it. The you seemed to argue that what might currently be in place is insufficient, but that wasn’t what this thread was talking about.
The only one showing ignorance here seems to be you suggesting subways use GPS.