PTC and signals

HemiAdda2d Dec 15, 2017

  1. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

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    On the northern transcon, signals used to be approach lit. Nowadays, specifically at grade crossings (diamonds) and some sidings, signals are always lit. Even with no movements coming. Others are dark until a train approaches within 5 minutes or so. Sometimes longer. I have waited upwards of an hour facing an approach lit signal with no movement.

    Is there a reason for signals to illuminate so variably before a train rolls through?

    Is there a reason the diamonds signals are all red in all 4 directions (CP/BNSF) when no trains are coming? Is this a PTC change?

    Just trying to understand signal operation to aid my railfanning efforts.
     
  2. Hardcoaler

    Hardcoaler TrainBoard Member

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    I'm uncertain. I too often find that signals at interlocked points are normally lit in all directions at the most restrictive aspect, but it's been that way for a long time here in the south at least. Maybe it's done as a sort of a no doubt, absolute stop safety provision? I despise approach lit signals, as we haven't a clue as to what's happening until the train is upon us. I always carry a radio scanner to help find trains. The rear end device frequencies are helpful, tho NS seems to have more powerful transmitters than CSX.
     
    Last edited: Dec 15, 2017
  3. Hytec

    Hytec TrainBoard Member

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    On the NS, ex-SOU NONE (New Orleans Northeastern), approaching the Slidell, LA (SDL) and Hattiesburg, MS (HBG) stations, the tri-color (Darth Vader style) signals are normally green until a train enters two blocks away when they turn amber. When the train enters the adjacent block, they turn red. I don't know what they turn when the train exits the station block because I now am on the train, ATK #20 for a relaxing ride to WAS or NYP..... :cool:

    Referencing Hardcoaler's comment about interlockings, the signal at the HBG station also guards the CN (ex-MidSouth, ex-IC, ex-Gulf & Ship Island) diamond. However the NS remains green until an NS train approaches or CN is granted clearance to cross.

    Thus, if you are modeling a specific area, try to find out how the company(ies) operate signals in that area. I'm guessing that alot depends on the operating procedures of the original lines that were bought up and/or merged into what exists today. Just a guess. ;)
     
    Last edited: Dec 16, 2017
  4. hoyden

    hoyden TrainBoard Supporter

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    I suspect the home signals can be controlled by the dispatcher. When I see a home signal lit it means the dispatcher has cleared a route but the train may be minutes or more away. OTOH when I see an approach lit intermediate signal lit I know there's a train nearby. I see all these behaviors regularly when I'm biking along the BNSF Wayzata Sub.
     
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  5. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

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    Define home signal? Like a signal delineating one block from another?
     
  6. hoyden

    hoyden TrainBoard Supporter

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    A home signal, or absolute signal, is used at interlockings and junctions. Intermediate, or automatic signals are used on the line between interlockings and junctions. A block could be delineated by either. If a block has a siding or passing track then the home signals will govern movement there. If a block is a section of track then it will be governed with an intermediate signal.
     
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  7. BoxcabE50

    BoxcabE50 HOn30 & N Scales Staff Member TrainBoard Supporter

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    A "home" signal is found along tracks approaching a junction or interlocking.
     
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  8. Suzie

    Suzie TrainBoard Member

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    Where there is a junction or crossing a route needs to be set for a train to proceed, and in this case all signals will be at stop until the dispatcher has set a route through. Once the train has passed the signal will automatically be returned to stop and will stay that way until a new route is set.

    On plain track signals are normally automatic and the dispatcher has no control over them. The aspect shown is dependant purely on the occupancy of the track ahead (can be several blocks) and whether it is lit or not usually depends on the available power source. In the olden days remote signals were powered from dry batteries so would only light when a train approaches to make the batteries last longer, nowadays power is more readily available in most locations so there is less need for approach lighting.
     
  9. mmi16

    mmi16 TrainBoard Member

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    Absolute Signals don't have a number plate attached to them. Intermediate signals do have a number plate (keyed to the mile post of the location).

    Trains can pass the most restrictive signal indication that a intermediate can display in accordance with the rules. Absolute signals displaying their most restrictive indication, STOP, cannot be passed unless the Train Dispatcher give the train formal permission to pass.
     
  10. jagged ben

    jagged ben TrainBoard Member

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    I'm sure the variation among prototypes depends on when the signal system was last upgraded and what the policies were at the time. It probably varied by subdivision on the same railroad as well. My understanding is that current UP practice is that signals at control points (a.k.a. absolute signals, a.k.a home signals in older parlance) are always lit whereas other signals are approach lit. But there are no doubt exceptions to this as well. Signal systems gain character over time as particular behaviors are instituted to address concerns specific to certain locations and track arrangements.

    I'm not aware if PTC regulations make any difference.
     
  11. BnOEngrRick

    BnOEngrRick TrainBoard Member

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    PTC regs don't make a difference in whether signals are approach lit or not, because the information regarding those signals is being transmitted through the PTC system either way.

    On the former C&O north of Fostoria, OH (only because I'm familiar with that section), the intermediate signals are dark until the dispatcher lines a train past a control point into that section of railroad. Once the train clears the entire section at the next control point, those signals will again go dark.
     
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