Discussion related to commuter rail and transit operators in California past and present including Los Angeles Metrolink and Metro Subway and Light Rail, San Diego Coaster, Sprinter and MTS Trolley, Altamont Commuter Express (Stockton), Caltrain and MUNI (San Francisco), Sacramento RTD Light Rail, and others...

Moderator: lensovet

  by Jtgshu
I remember driving an old Chevy passenger van, like a 92 or 93 with ABS. It has improved greatly over the years, as i remember in a snow storm, i could not stop becuase the ABS wouldn't let me, i just needed to skid for like a foot to bring the van to a stop, but it wouldn't and we just kept going at like 1mph with the pedal bouncing around and the thing making all this noise.....what a nightmare

You can tell im in train mode still from work earlier today becuase i had to re-read JBs post because I thought he was talking about ABS signaling at first :) not car ABS HAHAHAH
  by ThirdRail7
jb9152 wrote:
lensovet wrote:it would be like having an ABS system that's the same on all cars and doesn't take into account how fast the car is going or its weight or anything and saying "oh, ABS sucks! of course people can pump the brake better than this stupid machine!"
Also - this occurred to me as I gave it a bit more thought. ABS is not designed to guarantee a stop at a definite point in all conditions. It's a safety system that ensures that brakes don't lock up in a "panic stop" situation, at its core. It doesn't "think" or "analyze", per se. It simply helps the human operator not to brake his vehicle into an uncontrollable skid. Built into what it "knows" is the make and model of the car, its weight, and its basic performance characteristics. But that's about it.

PTC, on the other hand, has to be able to bring a train to a dead stop at a very specific point (or at least within some manageable, acceptable error band). It has to be calculating, on a second by second basis, the position, trajectory, and speed of the train and to be comparing that against what's in its physical characteristics database (which will provide permanent speed restriction locations, lengths, and speeds), its database of temporary speed restrictions (for temporary speed restrictions, lengths, and speeds...plus 'on the fly' restrictions that come up during the day as MoW requests track and time, foul time, etc.), and the states of all of the signal appliances in the vicinity (signal aspects, switch positions, and so forth). It has to do this for a trainset that might have different performance characteristics from day to day (especially in the case of freight trains), different engineers, and a different set of track conditions - dry, wet, high adhesion, low adhesion. There are certain things that the PTC system can "know" with accuracy, and others that it only "knows" to some lesser degree of accuracy. As Donald Rumsfeld once said, "There are known knowns;....known unknowns;.....[and] unknown unknowns." It's those known and unknown unknowns that force on-board PTC systems to add in "fudge factor" to their second by second stopping and reducing distance analysis.

This is why ABS is not an apt comparison, and also why there is some amount of safety margin built into PTC's calculations...which causes PTC, deployed as a simple safety overlay to existing train control systems, to be a drain on capacity.
Absolutely. Remember what happened at Ham Interlocking in New Jersey, which is ACSES equipped. There are too many variables. Plus, not too many people have mentioned what happens to the actual TRAIN as these things occurs.

BTW, did anyone actually see the texts that were allegedly sent? I'm not talking about as released from the NTSB or FRA. Has anyone seen the actual transcripts with their own very eyes?
  by Jtgshu
Yeaaaaaaaaaa Ham could have been bad.....really bad.....thank goodness it wasn't, by the hairs on our chinny chin chins.....

Its all good "in theory" putting the train into penalty braking if the engineer doesn't get it down in time, but what happens if he is trying and the condition of rails and/or equipment simply won't let him. After the fact you can say "well he should have had control of the train" but there are times when you loose control and not by your own doing.

I had a Geep go into Penalty and then Emergency all by itself after a cab signal change at 100mph. I got suppression and made it happy for a minute, (the cabs stopped beeping after acknowledging and suppression) then it hit me for some reason first with a Penalty, then Emergency. As i was sliding past the Approach at a speed faster than I should have been and wanted to be, imagine what was going through my head. Luckily the blocks were long...and the signal came up before I got to it. Maybe the dispatcher heard my call on the radio, I don't know, but either way, it was quite horrifying. If i was able to control the train myself, I would have been able to stop in plenty of time, but because control was taken out of my hands (not by my own doing), the only thing i could do was lay sand down, which should have been being put down already, but its something at least to counter that helpless feeling. We had no passengers, but I didn't know whats ahead causing that stop signal....

Look at the Cajon Pass wreck in 1989.

http://www.youtube.com/watch?v=OhOByrKb ... plpp_video

This is the whole episode of "Mayday" from the National Geographic Channel. The engineer was blamed at first, but then other factors were found to come into play....and as they say, it was doomed from the start.

NOTHING will be able to stop all accidents - no matter how good PTC or whatever they come up with is. I just hope people realize that. unfortunate as it is, its a truth....
  by 25Hz
Jt, thank you for the link to the video. You're right, no system will ever be error-proof.