While the basic goals were laudable, the (unfunded) PTC mandate was to install a system that had not even been fully designed yet. And, many people initially badly underestimated the complexity of the system that had to be designed and implemented. Most news stories still gloss over this complexity and make it sound as if the big bad railroads are intentionally dragging their feet.

There were a number of systems available elsewhere in the world that had a proven track record that could have been used -- except the specifications were intentionally written so that something new had to be designed. I've seen a number of these systems in use in Europe. At that point, they had a proven record and the bugs had been worked out.

I had a long (off the record) discussion with a fairly high official of an Eastern Class I railroad a number of years ago, who told me that among the problems found in early testing was that under some conditions, with closely spaced tracks, the track spacing was within the margin of error of the GPS system. In other words, the system could not tell on which of two parallel tracks the train was on. It's important to note that this applies only under some unusual conditions -- but any such situation is one too many.

-- Ernest