It is the controls and indications passed back and forth between onboard PTC gear and previously installed wayside equipment such as signals, switches, grade crossing warning devices, etc., that must be communicated in digital form over the radio, not the voice communication channels the engineers or conductors talk on.

Digital radio data transmission is nothing new. It has already been used for a number of years now. ATCS radio links that allow dispatchers to control and "See" the status of switches and signals along a CTC route, F.R.E.D.s, remote control locomotives, etc, all comes to mind. None of these prior uses of digital radio technology has caused the demise of analog voice radio yet. And won't - they are irrelevant to voice radio.

Eventually though, analog two way voice radio will cause its own demise; simply because the fierce competition for radio spectrum space, will make it too expensive to use so much space as analog requires.

Already, one of the big delays for implementing PTS is a severe shortage of frequencies that are available for the service; severe enough in fact, that it could be a show stopper in many areas. Of course, proving to be the toughest problem, is the gynormous task of creating precise electronic data bases of the exact location and properties of every single trackside appliance and fixture out there; every single bend and twist in the rail, and all special instructions covering every foot of track.

To put it more succinctly, each locomotive or cab car, must get itself "Qualified" on each PTS equipped line it operate on, just the same as any engineer would have to. In order to import such knowledge to a dumb machine though, that data must come from somewhere and be translated into machine understandable form; whereas, a human engineer merely needs to be exposed to the real world a few times, and he's got it. That is why railroads have hired hundreds (thousands in some cases) of minimum wage "interns" to create [G.I.S.] data bases.

Having professionally seen in past assignments to modern public transit agencies, the consequences in hundreds of safety critical errors finding their way into such databases; when put together by inexperienced unqualified and often incompetent interns; it scares the livin' hell out of me! It took years to root those errors out, and indeed, they are still being found. Unfortunately some of those errors were found the hard way, due to an accident investigation.

But the railroads have little choice here, as qualified experienced people in this field are in severe shortage across the country. Combine that with the irrationally short timeline politically dictated from on high..........

I would not hold my breath long for PTS to ever get into full service everywhere. And how long it will stay in service anywhere, after these very likely errors and omissions cause a wreck, is anybody's guess!