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Thread: American safety systems modeling

  1. #31
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    Okay, so we don't trust promotional videos. Which is fair. How about the NTSB report on the 1987 Chase, MD wreck? The information on the cab signaling system begins on page 32.

    On the corridor between New York and Washington there is a continuous-induction ACS system that repeats the wayside signal aspects on a four-aspect cab signal installed in the cabs of the locomotives. At the time of the accident, all locomotives and multiple-unit commuter cars operating on the corridor were equipped with these cab signals. As the train passes a wayside signal, the corresponding aspect of the cab signal is illuminated.
    The last sentence suggests that the cab signal reflects the signal that was just passed.

    However, there are some circumstances under which the cab signal can change while the train is in between signals. And perhaps that is what Vince saw on his cab rides. There are code change points located between some (not all) signal heads where cab signals can upgrade or downgrade based on changing conditions. However, the new signal tells you the aspect you should have seen last, not the one you will see next.

    At least, that is my reading of the report, which includes an illustration of Gunpow Interlocking and walks through a number of scenarios under which the cab signals might get downgraded:

    signals_gunpow.jpg

    On high-speed track 2 approaching Gunpow, there is a cab signal code change point, identified as CS-826, 4,749 feet south of northbound distant signal 816-2. If signal 816-2 were to change to an "approach" aspect because home signal 2N had changed to a "stop" aspect, then the aspect of the cab signal of a northbound train that had been running on a "clear" aspect on track 2 would have changed to "approach medium" at CS-826.
    So you're on track 2, and signal 816-2, which is further down the line, suddenly downgrades to Approach. You cab signals also immediately downgrade. But they do so to Approach Medium, which you hypothetically should have seen when you passed signal 836-2. They do not indicate Approach.

    A northbound train on track 1, having received an "approach limited" aspect displayed by distant signal 816-1 and thus concurrently displaying an "approach medium" on the cab signals, would have had the cab signals change to "approach" if home signal 1N changed to "stop" before the train reached CS-806. When the train reached CS-806, the cab signals would change to "restricting." If the train was already past CS-806 when the home signal changed to "stop," the cab signals immediately would have changed to "restricting" as a result of the loss of the code rate.

    Similarly, a northbound train on track 2 proceeding on a "clear" aspect received at signal 816-2 would have had a cab signal change to "approach" if home signal 2N changed from "clear" to "stop" before the train reached CS-806 and from "clear" to "restricting" at CS-806. Again, the cab signal would have changed to "restricting" if the home signal changed after the train passed CS-806.
    The same logic applies to an upcoming Stop at signal 1N or 2N. Your cab signals would downgrade to Approach, not Stop - up until the code change point CS 806, which point they would downgrade again to Restricting. Stop signals are a special case. There is a Restricting code sent out a couple thousand feet in advance, but this only applies to the area beyond the code change point, not to the entire block following the last Approach signal. And again, the cab aspect is known as Restricting, not Stop.

    In summary, if we assume Stop signals at 1N and 2N, this is how the cab signals would behave as Kuju programmed them:

    signals_kuju.jpg

    And this is how they should actually behave, if I've interpreted the NTSB scenarios correctly:

    signals_ntsb.jpg
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  2. #32
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    Quote Originally Posted by Vince View Post
    Here's a scenario:
    You are running under an approach indication and the next signal ahead is RED. You're saying saying the cab signal aspect is at approach? Sorry but my actual observation is the cab signal in this example shows STOP.
    The cab signal is at Approach up until the very last code change point before the Stop signal itself, at which point it changes to Restricting (Stop). This is what the NTSB docs suggest, and I believe this is what you saw.

    By the way, I have not modified your route's signal scripts. TCS scripts are strictly modifications of the engine.
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  3. #33
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    When you remove the wayside signals and place the rear end of the train ahead close to the "signal", you end up with the following train going past the red and slamming into the rear end of the train ahead. This doesn't work.







    Last edited by geepster775; 05-18-2020 at 10:48 PM.

  4. #34
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    The approach aspect would signal the engineer to slow down and prepare to stop before the next block. But, realistically, no railroad would remove the lineside signals without making some provision for an approaching-stop-signal zone, as the PRR did.
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  5. #35
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    This works.




  6. #36
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    You have to think of the cab signal system as super powerful wayside block signals that are visible throughout the entire block


  7. #37
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    Fixed it. Does this make the restricting concept more clear?



    (This is a fictional example. The IC used only 2 aspects.)
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  8. #38
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    Back to the shop you go.

    I hope its not a heavy train on a downgrade, what with barreling in on a green and having only 2/3rds of a block to slow and 1/3rd to stop.




  9. #39
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    There is a thing called the "overlap" which is a set distance in advance of the signal just passed by a train which has to be cleared i,e train not occupying it before the previous signal will clear from "stop" to "caution" therefore there is always a length of time when there are two stop aspects between trains.This allows for error and mismanagement of the brake by the driver.

  10. #40
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    Finally got to modern Amtrak safety systems on the NEC (ATC and ACSES). The script is not quite yet done, but it's very close to release - and, I hope, reality. Here's a demonstration video: https://youtu.be/SUGYjtR9lcY
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

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