You remember this from not so long ago, don't you:
"In much of Asia and Europe, engineers are protected by a technology known as positive train control or PTC." ?
It's from that long-winded but breathless, investigative but mistake-riddled piece of journalism that appeared in the NYT Sunday Magazine last month.
And then this happens: Two trains in Germany collide head on and at a high rate of speed.
Apparently the "much of Europe" protected by PTC doesn't include regional service in Bavaria.
Events have a way of exposing flaws in more than just journalism. The problem with waiting for events though, is that it usually costs somebodies some bodies.
So what did happen? After all, regional officials, transportation ministers or sub-ministers or deputy sub-ministers expressed befuddlement since an "advanced train control" system is in place and supposedly prevents this type of event.
See above comment about events.
The system of train control on this section of track is referred to in Germany as PZB, short for Punktförmige Zugbeeinflussung which translates as Punctual (or Punctuated) Automatic Train Control. Impressive name that, righ? But actually....
Actually, not. This is not a new system, having its initial applications in Germany in the 1930s. Actually, it's not automatic train control. It's an automatic train stop system only and only under specific conditions
Why do I say that PZB is not automatic train control? It is not automatic train control, because this system is not determined by, does not register automatically, and cannot respond to the vital factor for train control, conditions of track occupancy.
Instead PZB works in conjunction with a fixed signal governing entrance to a section of track when that signal displays stop, and that signal need not itself be connected to, or determined by the condition of occupancy of the track itself.
So if the human operator in charge of that signal maintains it at "stop," regardless of the condition of the track governed by that signal, PZB will enforce that stop requirement on the train approaching that signal .
And if the human operator changes the display of the signal to indicate "proceed," then regardless of the condition of the section of track--occupied/unoccupied-- the use of which the signal authorizes, movement will be authorized and PZB will release its "hold" on the train and allow the train to proceed.
Now why would a human operator do such a thing-- change the signal to indicate proceed when another train has authority and has occupied the track? Why would the human operator allow this overlapping of authorities?
Because...we're human. Because...I still dream about having written a dreaded lap order and I still wake from that dream cold, sick, glad it was just a dream, but not just quite sure it's only ever been a dream........like maybe I actually wrote a lap order once, but for reasons unknown, got away with it. Guilty conscience? Take it up with my therapist, Dr. Woodrow Allen.
Occupancy = vitality. And you want to know the great, great advance US railroads made in signal control systems? It begins way back in the 1870s, with the design, testing, and installation of the closed track circuit.
You know what that did? That separated the "office" from the "field" in the determination of track occupancy. Now the register of the condition of the track, occupied/unoccupied, no longer existed simply in the block operator's memory, or on the train dispatcher's train sheet, but in the field itself, and that register, that information could be communicated, by signals, to trains following and/or opposing that train's movement. Pure genius, almost.
I'm pretty certain, given the speed of the collision, that the section of track outside the stations between Rosenheim and Holzkirchen was not equipped with any mechanisms for registering occupancy, and communicating that occupancy to trains in the section. So once the signal was displayed and the westbound was allowed into the block, the only thing that might have prevented a collision was......sight distance.
Now it's possible that something else is the cause-- that something somewhere malfunctioned to produce a "false clear"-- the signal engineer's nightmare, equivalent to the train dispatcher writing a lap order-- and that the human operator in charge of the signals did not improperly authorize movement into the section of track.
That's possible. But that doesn't change the fact that such systems as PZB do not remedy the underlying, and fatal, weakness of any train control system that is not based, first last and always, on the separation of the field from the office in determining occupancy.
February 11, 2016
No buzzwords allowed.