I was thinking the same thing and wondering what the use case may be for doing this via radio - thanks for clearing it up! But once you use unencrypted radio, y

I was thinking the same thing and wondering what the use case may be for doing this via radio - thanks for clearing it up! But once you use unencrypted radio, you open it up for remote exploitation - the same thing that can be sent from close up can also be sent from further away with more powerful equipment. That's probably why the systems I was aware of until now use magnets on the track (this can of course only be used to make sure trains stop at a signal, or respect the speed limit, not for arbitrarily stopping them).