My specialty area is not cognizant of dispatching details. The dispatchers tell the trains what to do; the PTC system tells the trains whether they may do it at all.
However a common problem causing wrecks is crews fallen asleep or that otherwise blow by a signal. If they are not alert to signals, I doubt that they care about the radio either. PTC gets around this by stopping a train heading into danger even if, hypothetically, its whole crew was knocked out.
Maybe it’s just a case of local action where helper locos and crew have to interact with many trains getting over the hump. Everybody is awake because of the coordination needs.
I would suppose that a crewman could spend years, or even an entire career without ever encountering an unexpected red signal, and if this is true, it would make anything approaching 100% vigilance virtually impossible, in human terms.