PTC was originally a very broad catchall term, intended to refer to any technology that could actually prevent a train from exceeding its limits. Unfortunately, the term has been hi-jacked by certain vendors to specifically mean their particular type of technology. But the industry as a whole is not so stupid as to buy into that - I know, because I've been asking around, as I meet colleagues from around the country. It is only the political types that are giving us grief.

But even more unfortunate, is that no technology man or god will ever devise, can cover all the strategic realities of running trains. There will always be tactical holes you can drive a truck through - or a train through! Whatever technology you use to control your trains, the question remains, just how many of those holes will you decide to actually plug. What has come to be referred to as PTC, has no particular advantage over existing technologies; which can be and have sometimes been so arranged, as to do all of what so-called PTC can do, for a lot less money - Salt Lake City, for example, TGV for another.

That existing train control systems did not always plug some of those holes, from 1920s on was merely a choice, a corporate decision (an unfortunate one); the technology was there. But in some places, better choices WERE made. The current radio based proposals will not exceed those better choices, and will, as it stands now, be a step backwards.

I will grant, that these newer technologies are considerably better than a "Lap Order" in dark territory. They are also better than an overrun into work limits, and will also be useful in providing some finesse executing train meets, to save fuel. They will also be immensely beneficial in helping the locomotive engineer control his "train dynamics". These are the original reasons the A.A.R. started this research in the first place.

And yes, you are correct, that as currently developed, PTC must be fully be integrated with any system now existing, so that it can report actual ground conditions to the trains. It is and always will be, totally dependent on existing wayside appliances, especially track circuits, for all its safety critical data. But to accomplish this integration is absolutely daunting - and expensive to the extreme. I know, I have spent thousands of hours over the years in efforts to do just that. And that was just mere peripheral involvement. That particular effort was eventually scrapped - too many unsolvable safety issues and way too much ARPA money spent (wasted actually).

If it ever happens, it will take ten or twenty times more people than currently have that skill set (railway signaling); not to mention, a huge bailout from the gov't (maybe as much as a cool trillion). The railroads are already asking for massive delays and financial relief. That is partly what is making certain Senators angry - the handwriting is already on the wall, PTS ain't gonna happen soon!

Still, very critical safety problems arise when we try to communicate commands or authorities to actual trains via radio. This is where we still fall flat on our faces. It is absolutely safety critical, that ONLY the right train gets the right authorities at the right time. To do that, the system must continuously determine with absoluteness, which train is on what track, and where. Then it must actually properly address the command, because all trains in the area will receive it. But it can't continuously do that! The train must instead remember picking up some transponder somewhere, and then use that data way after it has become stale. Just imagine pulling out into traffic, based upon remembering a previous look down the road!

Now what if it picked up the wrong transmission, and thus places itself on the wrong track, the error will inevitably perpetuate itself until it becomes fatal. With no chance of correction by continuous and fresh detection, the result of even the first error, is an almost certain head-on collision. No matter how the radio based technology was organized, this problem has reared its ugly head time and again. Literally hundreds of millions have been spent trying to resolve this in a safety critical manner - to no avail.

But coded low frequency or coded DC track circuits can do all the safety critical functions needed for PTS (original definition), and inherently without any of these safety critical problems. Only a train actually in the circuit can even physically receive what it transmits. More over, no railroad I know of uses audio frequency track circuits like the ones at WMATA, for train control purposes; so they have not had WMATAs problems, and never will have.

It is my, no longer humble opinion (it is now a firm belief based on long experience), that we will achieve a really meaningful PTC functionality much more quickly by adjusting and fully using what we already have, first. Then simply let progress with the newer technologies come in by the very natural evolutionary process that always has been how new invention happens. If we don't artificially rush it, it will happen sooner.

And political decisions are always artificial. Political forces are going to end up screwing this pooch, if we are not careful!

Now, I had better get hot on some real work!

OPB