It's very difficult to BRIEFLY (locomotive engineer trying to explain train handling to a non-engineer)answer your questions above, Matt Mitchell, but I will try.
Issue 1: Yes you are right! In the scenario you describe, one train following another, your conclusion is on target. The problem is that you have no way of KNOWING if you are following someone, therefore you don't know how to procede as far as backing off the track speed a little to allow the guy to get ahead of you, or keep on throttling up when the signal magically goes up to clear for whatever reason to maintain schedule. Its all about the uncertainty. An engineer has to be able to anticipate, somewhat, based on fixed signals, track conditions, speed restriction, etc. on how to govern his/her train. Cabs with no waysides (Rule 562) isn't a bad thing in and of itself. I think it would be a wonderful system along the individual branches instead of the system trunk from Glenside south because of the congestion of trains that operate through that area. One could argue to just operate at 45mph the whole way, but now you are delaying the train. You can't tell the dispatcher that I went slower because I THOUGHT the cabs were going to drop, or I THOUGHT that I was following somebody. It won't fly!
Issue 2: The answer to the first part of your question is yes, there are fixed block locations where the cabs usually, but not necessarily drop at (I can tell from the impedance bonds in the track gauge). The new "blocks" are actually quite longer than the old ABS blocks were. In good rail conditions (non slippery rail), the cabs dropping would be more of a headache than anything else; when slippery rail occurs (light drizzle on dry rails, morning dew, and the worst of all leaf season) it really becomes a concern. What you have to understand is that with wayside signals, the engineer can SEE way ahead what the track conditions are, and operate the train accordingly. The new system doesn't afford the engineer this luxury. You don't drive your car through a green light thinking that it's going to go right to red. In an engineers case, we can't operate the train hoping that the cabs won't drop. I mentioned above that any signal drop in the cab signal system forces the engineer to apply a considerable amount of braking effort to suppress the penalty, which during slippery rail season can cause an engineer to lose control of their train. I'll give an example, on the Harrisburg line. The ROW from Paoli east into Zoo is mostly downhill. Let's pretend its leaf season, which the Paoli line is notorious for being one of the worst to operate. I leave Haverford station approaching Ardmore with caution so I don't slide through it. Just east of Ardmore is an automatic block signal, and with that signal I know the conditions of the track ahead, including the signal DOWN THE WINDING HILL at OVERBROOK INTERLOCKING. If the signal at Ardmore is at clear, then I'll still have to be careful not to slide through the stations on the downgrade, but I know I have railroad down the hill at Overbrook; however, if the signal is at APPROACH MEDIUM I know as a qualified engineer that by signal progression the next signal at Narberth (distant to Overbrook) is likely at APPROACH and Overbrook is at stop. I know all this even before I come into Ardmore. If Rule 562 were in effect there, I would leave Ardmore, likely under a clear, and I would either have to go even slower than I normally would because of fear of cabs dropping (after all, I don't know what the conditions ahead are until I hit that drop point) thus delaying the train, or take my chances, lose control of the train, and quite conceivably slide all the way down the hill. Scary thought isn't it. With that signal at Ardmore, I know what the track conditions are for the next 3 MILES(the distance between Overbrook and Ardmore)
And yes, cabs can drop at any time from clear to restricting.
Issue 3: False on all counts, Amtrak operates trains in excess of 125mph with cabs and waysides in conjunction with one another on the NE corridor everyday. In fact, trains on SEPTA territory are actually SLOWER now then they were before the project began, its just that the schedule padding helps soften the blow. (I mention some of the few instances in an above post) An engineer is supposed to operate at the more restrictive speed if the Cab signal display does NOT conform to what the fixed signal is within 6 seconds of passing it. For instance, If I go by an APPROACH on a fixed signal, my cab signal should conform to the approach in the Aspect Display Unit within six seconds, which would be a cab signal conformity. On the other hand, if I went by a fixed signal indicating STOP and PROCEED (restricting is the cab signal conformity) and the cabs went immediately to CLEAR after passing the STOP and PROCEED, that would be a cab signal nonconformity and I would have to operate at restricted speed through the entire block, until my entire train (on SEPTA territory, leading wheels by NORAC RULE) passes a more favorable FIXED signal indication, despite the nonconforming CLEAR in the Cabs. If the Cab signal system doesn't conform at TWO CONSECUTIVE fixed signals, than by NORAC rule that would be a Cab signal failure.
Now, if it were slippery rail conditions, and I wanted to maintain control of my train, I would begin reducing my speed way ahead of a fixed signal that I KNOW would force me to suppress a penalty (APPROACH MEDIUM, APPROACH, APPROACH LIMITED, etc.) so I don't have to Lock up my wheels (which causes the decelostats to go crazy and the trains really starts sliding) trying to suppress a penalty. I see your point about anticipating signal drops, and if I had reason to believe they were going to drop (i.e. a fixed signal inidicating anything other than a clear) I can anticipate much better how to govern my train, as opposed to wondering if the signals MAY or MAY NOT drop. Its not practical, between Jenkintown and Wayne, to constantly apply the brakes at drop spots or operate at lower speeds for fear of losing control of my train during slippery rail conditions, and I shouldn't have to.
What I cannot emphasize enough, is that it is difficult to explain the dilemna to one who does not operate trains daily and make it make much sense. It is an onerous task to condense into paragraphs a logical paradigm for non-locomotive engineers to understand what for prospective engineers takes months of extensive training to learn through classroom teaching, qualifying, and on the job training to master. Rule 562 looks nice on paper, but it really has a lot of holes in it, particularly with SEPTA's application of it. Operating a train is not like driving a car. The engineman has to have some idea how to govern the safe, comfortable, and punctual movement of their train. The West Chester branch has cab signals and waysides, along with bidirectional signaling on both tracks; I believe that that system is far better than what SEPTA has incorporated recently between Wayne and Jenkin. What are the advantages of having rule 562 in effect on SEPTA's mainline over incorporating Rule 261 (bidirectional track signaling) in conjunction with waysides? Less signals to maintain, less bulbs to change! Big deal!
I won't even get into what happens when there is a cab signal failure. Please note that there are two qualified locomotive engineers complaining about the same problems on this post.
Last edited by whovian on Thu Feb 02, 2006 2:12 am, edited 6 times in total.