The general principle in railway movement authority is that there's an easy fail safe: stop moving. If nothing moves, there can be no collision.
If something goes wrong? Stop the train. You can then figure out what went wrong and address it with no risk. Things shouldn't be going wrong, speeds shouldn't be being exceeded, etc.
If no train on the line moves, sure. But stoping just the one train won't improve safety, and was historically the cause of many accidents. I remember just the one in Shanghai in 201x. One train stopped, the following train hit it.
That shouldn't happen under normal circumstances. That's whole idea behind railway signals.
Rail segments (blocks) are supposed to be automatically locked off while a train is on that segment of track. No two trains can be on the same block at the same time. If a train stops, the signal guarding that block will remain red, ordering the next train to stop before it gets anywhere close.
Europe may has that, with the GSM-R system. I remember reading of at least one minor accident that stayed minor because the driver to discover the landslide over the track at low speed passed the button, stopping the incoming faster train on the other track.
AFAIK, this is just a Czech extension to GSM-R. That said, I recall various instances of GSM-R being used in the UK to broadcast a general message to stop, albeit one that the driver has to act upon.
That's an interesting way of looking at the cause and effect. Trains unexpectedly stopping in an expected and inevitable property of all networks, whereas trains exceeding their movement authority is not.
Stopping a train anywhere should therefore always be safe, so the safety failing is with the train behind, not the one in front.
Even then you should have some give aka Speed of X+3 MPH break, speed of x+1 MPH warning. You want fault tolerance not simply a hard limit without feedback.
Just a PID speed controller, maybe. Then, some boundary condition where when the controllers inputs mismatched from predicted outputs, then throw an error. But, if you're trying to drive 45, and you achieve 46 with a tail wind it doesn't seem necessary or safer to stop the train.
If something goes wrong? Stop the train. You can then figure out what went wrong and address it with no risk. Things shouldn't be going wrong, speeds shouldn't be being exceeded, etc.