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Thread: signal question

  1. #1
    Join Date
    Nov 1999
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    Albuquerque, NM
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    434

    Default signal question

    I was out railfanning on the Craig branch of the UP in Colorado (old Moffat line), and I noticed that all of the automatic block signals (the ones between sidings on single track) look like this. Sometimes they are mounted on separate poles (one for each direction).

    [Link Expired]

    Without fail, the dual-head signal is for uphill traffic. Anybody know why this is, and what the second head is used for?

    Mark

  2. #2
    Join Date
    May 2003
    Location
    Shelby, Ohio, USA.
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    109

    Default RE: signal question

    The signal probably has 2 heads because it is a distant signal to an interlocking signal. On CSX if the interlocking signal displays limited clear, the intermediate signal will display approach limited, which would give the crew advanced warning that they will be crossing over at the next interlocking and are not to exceed limited speed. Hope this explains it.

    edit: Check out Al Krug's site -- it explains it all. http://www.coffey.com/~alkrug/rrfact...ls/signals.htm

    -csxac44_69

  3. #3
    Join Date
    Nov 1999
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    Albuquerque, NM
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    434

    Default RE: signal question

    That's what I thought at first too, but the two-headed signal is present at every block signal installation, not just the ones prior to an interlocking, and only on the side for uphill traffic. I'm guessing that the uphill thing has something to do with it, but I can't figure what.

    Mark

  4. #4
    Join Date
    Nov 1999
    Location
    Jefferson, Texas, USA.
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    419

    Default RE: signal question

    Well, this may or may not be the answer...but I do know that on many railroads, ABS signals at the approach to a grade are marked with a "G" placard so that really heavy trains can actually pass restricted indications (of the correct variety of course, when following other trains) without the traditional "stop and proceed"

    Possibly that's what the second head is for. Rather than having a "G" for "grade" placard, the second head serves to allow heavy trains through the signal.

    Just a guess, but it'd make sense considering your description.

  5. #5
    PatchCrew Guest

    Default RE: signal question

    Mark:

    Are the signals in your picture the ONLY ABS signals between sidings?

    If so the dual signal head would be used to display a double yellow which is called an "Approach Diverging" on UP. A double yellow would be displayed to indicate to the train crew that they will be going into the next siding.

    Now as to why they are used uphill only, my educated guess would be so the crew on a train going uphill would know in advance that they would be going into the next siding. If just a single head signal was there then it would display a yellow indication and the Engineer would have to slow down expecting the next signal to be red, only to find out that the next signal is displaying a red over yellow which means he will be going into the siding. So you see the Engineer would have to slow down while going uphill prepared to stop at the next signal and he possibly would stall his train or break a knuckle (or drawbar) when he saw he had a more favorable indication than a red. The Approach Diverging signal gives him ample warning so he does not have to slow down except for if he needed to slow down for the turnout speed.

    I guess on this line, UP (actually SP/DRGW) felt that an Approach Diverging signal was not needed downhill.

    On the routes that I work, only some of the sidings have Approach Diverging signals.

    Again this is only my guess as I do not know the actual route in the picture.

    >ABS signals at the approach to a grade are marked with a "G" placard so that really heavy trains can actually pass restricted indications

    Blake when a signal has a "G" plate it applies to ALL trains and not just the heavy trains. I can't see why a lighted "G" would be needed (might be though) and remember these are ABS signals which are not controlled by the Dispatcher. And a "G" plate signal is a restricted indication. You meant to say a signal would have a "G" plate so a Stop indication could be passed. :-)

    One other thing. Al Krug's site does not list UP signals. BNSF and others use signals we don't have (at least on ex SP western lines) so we don't have distant signals (actually a distant signal is something entirely different on UP and is used only in NON CTC territory) and we don't have limited speed signals on western lines either. There is no standard among railroads for signals and in fact the UPRR uses different signals on its original lines than the lines of the ex SP/DRGW routes.

    PatchCrew
    UP Engineer

  6. #6
    Join Date
    Nov 1999
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    Albuquerque, NM
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    Default RE: signal question

    >Mark:
    >
    >Are the signals in your picture the ONLY ABS signals between
    >sidings?

    No. They are all over the place. There are several in a row in places where the sidings are spaced kind of far (which is common on the Craig Branch). Is it possible that the bottom head will display lunar, so that it would be red/lunar, thus giving a restricting indication, so that uphill trains don't have to stop?

    Incidentally, I only saw one of these signals lit once, and a MOW truck was on the tracks approaching the two-head side (going uphill), and the top head was red and the bottom head was dark.

    Signals are fun, right?!

    Mark

  7. #7
    Join Date
    Nov 1999
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    Albuquerque, NM
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    Default another clue

    Here is something that may help to clear up things. This is an automatic block signal on the Moffat Sub, on the dotsero cutoff between Dotsero and Bond. It is a bi-directional signal, but it has a second single-light head, again, for the uphill traffic. What do y'all think?

    [Link Expired]

  8. #8
    Join Date
    Nov 1999
    Location
    Colorado, USA.
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    992

    Default RE: another clue

    The single light is a restricting signal (white). The rest I need to look up.


  9. #9
    PatchCrew Guest

    Default RE: another clue

    >Is it possible that the bottom head will display lunar, so that it would be red/lunar, thus giving a restricting indication, so that uphill trains don't have to stop?

    Yes I thought about that also except a lunar indication is something the Dispatcher would have to give. Remember you said these are ABS signals so they are not controlled by the Dispatcher as they only check the track conditions automatically in the block ahead.

    Another possibility would be that they are "P" plate signals. A "P" plate signal is used in conjunction with high water and rock/slide detectors. A red signal would be displayed and the letter "P" would light up in the bottom mast indicating to the crew to check the track ahead before proceeding. But if that is the case why uphill only?

    I have no other ideas as there is nothing in the UP System Special Instructions that would explain a logical use. An ABS signal displaying a red over dark is a Stop and Proceed signal. An ABS signal displaying a red over red is a Stop and Proceed.

    >The single light is a restricting signal (white). The rest I need to look up.

    Ok so if they are ABS signals what triggers the lunar indication?

    PatchCrew
    UP Engineer

  10. #10
    Join Date
    Nov 1999
    Location
    Colorado, USA.
    Posts
    992

    Default RE: another clue

    Mark

    From W Phippsburg to Evans, its all CTC (not ABS) and from Bond to Phippsburg its CTC. No ABS up there.

    Just a reminder:
    Automatic Block Signal System (ABS)
    A series of consecutive blocks governed by block
    signals, cab signals, or both. The signals are activated by
    a train or by certain conditions that affect the block use.


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