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Thread: Modern railroad signals

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    LOL! There's also a "vanishing" train... at the 100m zoom level, you can see a southbound freight on the CSX line waiting for the coal drag to complete the crossover - and you can see the whole coal drag. Zoom in one click to 50m, and the southbound CSX vanishes along with the head of the coal drag.

    At the 100m zoom level, there's also a THIRD train north of the crossover (V) ... the coal drag is actually crossing from the lower-most double track through the crossover (V) *and* the junction (X-Z).
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    TD, thats awesome! It does help me a lot.

    I hate to go sideways on you but how did you get that interactive google map in the post?? I would love to be able to do that. I have several areas I would like to post and talk about and that would make it a lot easier!

    Yes, that is a CSX yard just down the tracks. If you follow the tracks on around lookout mountain (to the right) it will take you to the NS yard which is huge! They have a humpyard too.

    Be the kind of person your dog thinks you are.



    Ron

    For now, innocent bystander and occasional commentator

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    Quote Originally Posted by REM37411 View Post
    TD, thats awesome! It does help me a lot.

    I hate to go sideways on you but how did you get that interactive google map in the post?? I would love to be able to do that. I have several areas I would like to post and talk about and that would make it a lot easier!

    Yes, that is a CSX yard just down the tracks. If you follow the tracks on around lookout mountain (to the right) it will take you to the NS yard which is huge! They have a humpyard too.
    The "Map" tags... [ MAP ] 365 Wauhatchie Pike, Chattanooga, TN [ /MAP ] ... I added the spaces so the tags would show. You can also click the "Map" button in Advanced mode... it's on the bottom row of formatting buttons looks like a little map (you can barely make out an interstate highway sign on it). The content between the tags is a street address, not a lat/long (haven't tried that, don't know if it'll work).

    Yeah, that NS yard is massive...
    Never mistake a guy who talks a lot for a guy who has something to say...

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    Quote Originally Posted by TwinDad View Post
    I'd be curious to know how automated/integrated these signals actually are... for instance... if signal D is at "Stop" and the junction crossover is thrown (Z-X) then signal "A" should be at "Diverging Approach" (at best)... but if signal D is a NS signal and signal A is a CSX signal... ??

    Or maybe C/D belong to CSX also... but then E and F/G may have to reflect the signal at C... same problem...
    The signals are absolutely interconnected. If the signals were not, then the most permissive aspect that would be allowed into the crossover between CSX and NS would be a restricting aspect. The signals on the crossovers might be able to show something more permissive, but a train would still have to slow to restricted speed before entering the crossover.

    Paul

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    Quote Originally Posted by pbender View Post
    The signals are absolutely interconnected. If the signals were not, then the most permissive aspect that would be allowed into the crossover between CSX and NS would be a restricting aspect. The signals on the crossovers might be able to show something more permissive, but a train would still have to slow to restricted speed before entering the crossover.

    Paul
    So... how is it done... does one company or the other control ALL of the signals on behalf of both, or do the two company's systems communicate with each other to negotiate (I suppose in these modern times automagically) the appropriate aspects throughout the interlocking?

    Or is it that since they're (probably) "just" ABS signals, it's more of a self-contained automatic system that isn't really controlled by either company... they just react automatically to the switch positions and occupancy detection from the surrounding track blocks?
    Never mistake a guy who talks a lot for a guy who has something to say...

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    Quote Originally Posted by TwinDad View Post
    So... how is it done... does one company or the other control ALL of the signals on behalf of both, or do the two company's systems communicate with each other to negotiate (I suppose in these modern times automagically) the appropriate aspects throughout the interlocking?
    The signal systems communicate through the rails and/or through seperate code lines. These are vital circuits with a fail safe requirement on the prototype. All of the information is concerned with occupancy ( occupied in this case is actually triggered by either a short circuit ( when equipment is in a block ) or an open circuit ( due to a break in the rail or an open switch )).

    None of the technology here is new by any means. CTC has been around since well before WWII.

    Or is it that since they're (probably) "just" ABS signals, it's more of a self-contained automatic system that isn't really controlled by either company... they just react automatically to the switch positions and occupancy detection from the surrounding track blocks?
    Most signals in the US today are automatic signals ( varriations of either ABS or APB ).

    When the signals are controlled by a tower operator or the dispatcher through CTC, the operator can only set the signals to a more restrictive setting than track conditions allow. This means a dispatcher can set a route through an unoccupied switch or set a turnout to stop that might otherwise display proceed, but not vice versa.

    Operator controlled signals ( either those controlled through CTC or through a tower ) are always absolute signals that default to the stop position. Intermediate signals are always automatic signals. In CTC territory, signals give permission for a train to enter the next block at a prescribed speed.

    In non CTC territory, the signals are all automatic, but, the signals only report the condition off the track ahead, but they typically do not give an operator permission to proceed into a block. ( I say typically here because I think there may be an exception for two mainines that are signalled for mement with the current of traffic (I.e. signal led as single direction mainlines ).

    The few signals that are not automatic in the US today are generally related to crossings at grade ( diamonds). Gates and smash boards can fall into this category. These signals may be preceded by fixed aspect signals, and can actually be interlocked with automatic signals ( through the use of electronic locks ). I have never seen a manual signal that wasn't a mechanical device.

    Paul

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    Quote Originally Posted by pbender View Post
    The signal systems communicate through the rails and/or through seperate code lines. These are vital circuits with a fail safe requirement on the prototype. All of the information is concerned with occupancy ( occupied in this case is actually triggered by either a short circuit ( when equipment is in a block ) or an open circuit ( due to a break in the rail or an open switch )).




    ALL signal circuits in the US are automatic signals ( variations of either ABS or APB ).

    When the signals are controlled by a tower operator or the dispatcher through CTC, the operator can only set the signals to a more restrictive setting than track conditions allow. This means a dispatcher can set a route through an unoccupied switch or set a turnout to stop that might otherwise display proceed, but not vice versa.

    Operator controlled signals ( either those controlled through CTC or through a tower ) are always absolute signals that default to the stop position. Intermediate signals are always automatic signals. In CTC territory, signals give permission for a tain to enter the next block at a prescribed speed.

    In non CTC territory, the signals are all automatic, but, the signals only report the condition off the track ahead, but they typically do not give an operator permission to proceed into a block. ( I say typically here because I think tere may be an exception for two mainines that are signalled for mement with the current of traffic (I.e. signal led as single direction mainlines ).

    Paul

    Paul
    Thanks for that.

    But I don't think I was clear about my question...

    The two companies own their respective tracks... and (IIRC) traditionally (or by law?) whoever came along second and asked for / built the crossover (Z-X, the junction) is responsible for its maintenance, and presumably also the signals immediately related to it...

    Nevertheless, at some location in this area there's a boundary between "stuff CSX owns/operates/maintains" and "stuff NS owns/operates/maintains". Doesn't much matter exactly where that boundary is, but there are signals (and dispatchers) on one company's tracks that need information from track sensors that the other company is responsible for.

    How do they manage shared access to the information and coordinate their respective signals? Does CSX simply tap into NS's track circuits where needed (or equivalently does NS provide the taps for CSX to use)? Do they share the occupancy information at some higher level... via their respective dispatching computer systems?

    I'm probably still mangling my question, but let me put it one more way... regardless of how the sensing/signaling system physically/electrically works, there's a business relationship that must be arranged here about who is responsible for what, and who provides what information to whom, and at what level of communication (direct access to track circuits, higher level computer interface, radio comms, carrier pidgeon, etc.)? That's what I'm curious about.

    My guess would be, having rambled for four paragraphs now... that each company provides the other direct "taps" (for lack of a better word) into the other company's track occupancy sensors, for however far up/downstream is necessary to provide the required information (likely just in the immediate vicinity of the junction). Access to and maintenance of these "taps" would I presume be via some form of agreement between the companies that is mutually beneficial (tit for tat, quid pro quo, share alike, etc. "you show me yours...")

    This would seem to be the simplest, and thus most fail-safe solution... but it's been my experience that generally businesses - especially competitors - don't like to share information (and assets) at a low level, preferring to work at the highest level of interaction that allows the job to get done, keeping as much as practical at "arms length". I'm wondering if this sort of situation is an exception, whether borne of necessity, or rule, or practicality, or whatever, or rather if they actually communicate between the respective systems at some higher level (e.g. dispatchers messaging each other somehow, then setting their own systems accordingly).

    Maybe, as is often the case, I'm just over-thinking this.
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    Quote Originally Posted by TwinDad View Post
    The two companies own their respective tracks... and (IIRC) traditionally (or by law?) whoever came along second and asked for / built the crossover (Z-X, the junction) is responsible for its maintenance, and presumably also the signals immediately related to it...
    True, when two railroads cross. Where two railroads link to oe one another, there could be other arrangements going on ( trackage rights, for example ) because the rail system only works when different carriers interchange cars.

    Nevertheless, at some location in this area there's a boundary between "stuff CSX owns/operates/maintains" and "stuff NS owns/operates/maintains". Doesn't much matter exactly where that boundary is, but there are signals (and dispatchers) on one company's tracks that need information from track sensors that the other company is responsible for.

    How do they manage shared access to the information and coordinate their respective signals? Does CSX simply tap into NS's track circuits where needed (or equivalently does NS provide the taps for CSX to use)? Do they share the occupancy information at some higher level... via their respective dispatching computer systems?
    This is all done with track circuits.

    When a train moves from one railroad to another, someone ( probably the train crew ) will contact the dispatcher asking for permission to enter his track. You will hear these conversations if you listen to the radio traffic. In the case of the interlocking plant in this thread, The two signals on the crossover between NS and CSX are the ones used to convey authority to proceed onto the other line.

    Paul

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    Quote Originally Posted by pbender View Post
    True, when two railroads cross. Where two railroads link to oe one another, there could be other arrangements going on ( trackage rights, for example ) because the rail system only works when different carriers interchange cars.



    This is all done with track circuits.

    When a train moves from one railroad to another, someone ( probably the train crew ) will contact the dispatcher asking for permission to enter his track. You will hear these conversations if you listen to the radio traffic. In the case of the interlocking plant in this thread, The two signals on the crossover between NS and CSX are the ones used to convey authority to proceed onto the other line.

    Paul
    So... the signals around the area tap into whatever track circuits they must in order to figure a correct (safe) aspect, regardless of the track circuit's owner (again I assume some business agreement that allows this... it would in fact be mutually beneficial, after all)...

    IIRC, if this is anything but CTC territory, even if the signals at C/D showed "Clear" ... the train could not cross the boundary without a clearance from the (other railroad's) dispatcher... the signals do not convey authority, after all, only status. So as you say, they'd have to either radio ahead (most likely) or stop at the crossing, regardless of the signal aspect.

    If it *is* CTC territory, then it *could* be that, for example, the CSX dispatcher controls signal C (and the NS dispatcher signal D)... and can stop a train crossing over from NS territory by forcing signal C to "Stop"... and then grant authority by releasing this hold... at which time the signal will automatically change to the right aspect for the dowstream track conditions... which could be anything from "Stop" to "Diverging Clear" ...

    I think a very, very dim lightbulb is slowly starting to glow ever so faintly inside my thick skull...

    @Ron, I hope I haven't totally derailed your thread...
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    I'll add my casual observations...

    Signals A, B, D, and turnout Z are controlled by the CSX Dispatcher. Turnout Y is a hand-thrown switch most likely NOT equipped with an electric lock.

    Signals E, C, F, G, and turnouts W, X, and crossover V are controlled by the NS Dispatcher.

    Since signals D and C are located where they are, it appears turnouts X and Z are NOT wired together, or "interlocked".
    In other words, the CSX Dispatcher can REVERSE his turnout Z to align a northbound train towards the NS, then request his Signal A to display something better than STOP; but the NS Dispatcher must REVERSE his turnout X before he can request his Signal C to display anything more favorable than STOP. So, given the hardware on site, I don't believe the CSX and NS signals/turnouts "talk" to each other.

    Signals D and C mark the "property line" between CSX and NS; and each company's signal system cannot convey authority beyond their own rails and onto the other guy's track.
    In other words, NS Signals F and G only "control" the following track: both NS mains up to turnout W and the single track south thereof, and the crossover track beyond turnout X up to Signal D only.

    Signal A is the "distant signal" to Signal C.
    Signals F and G are the "distant signals" to Signal D.
    Given the short distance between A and C and F/G and D, in the event Signals C and D are "Stop" the best aspect you'd get at Signals A, F, and G would most likely be "Restricting".
    In other words, the CSX Dispatcher could REVERSE turnout Z and display a signal at A for a northbound train to head for the NS track. But the NS Dispatcher has a southbound train lined up through Signal G-crossover V NORMAL-turnout X NORMAL-turnout W REVERSE. So, the northbound CSX guy would pass Signal A, displaying a Restricting, and pull up to and stop short of Stop Signal C until the NS southbound gets by Signal E.

    Clear as mud?

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    Quote Originally Posted by TwinDad View Post
    So... the signals around the area tap into whatever track circuits they must in order to figure a correct (safe) aspect, regardless of the track circuit's owner (again I assume some business agreement that allows this... it would in fact be mutually beneficial, after all)...
    Correct.

    IIRC, if this is anything but CTC territory, even if the signals at C/D showed "Clear" ... the train could not cross the boundary without a clearance from the (other railroad's) dispatcher... the signals do not convey authority, after all, only status. So as you say, they'd have to either radio ahead (most likely) or stop at the crossing, regardless of the signal aspect.

    If it *is* CTC territory, then it *could* be that, for example, the CSX dispatcher controls signal C (and the NS dispatcher signal D)... and can stop a train crossing over from NS territory by forcing signal C to "Stop"... and then grant authority by releasing this hold... at which time the signal will automatically change to the right aspect for the dowstream track conditions... which could be anything from "Stop" to "Diverging Clear" ...
    Correct in both counts, and I mentioned ths previously.

    Paul

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    Quote Originally Posted by SooLineRob View Post
    I'll add my casual observations...

    Signals A, B, D, and turnout Z are controlled by the CSX Dispatcher. Turnout Y is a hand-thrown switch most likely NOT equipped with an electric lock.
    Since this is inside an interlocking plant, turnout Y is definitely electrically interlocked with the signals. If it was not, an engine parked on the siding could be run onto the mainline even if turnout Z were lined for NS.

    Signals E, C, F, G, and turnouts W, X, and crossover V are controlled by the NS Dispatcher.

    Since signals D and C are located where they are, it appears turnouts X and Z are NOT wired together, or "interlocked".
    [I]In other words, the CSX Dispatcher can REVERSE his turnout Z to align a northbound train towards the NS, then request his Signal A to display something better than STOP; but the NS Dispatcher must REVERSE his turnout X before he can request his Signal C to display anything more favorable than STOP. So, given the hardware on site, I don't believe the CSX and NS signals/turnouts "talk" to each other.
    The aspect CSX signal A can display depends on what signal C displays. What signal C displays is dependent on the position of crossover V.

    Paul

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    Quote Originally Posted by pbender View Post
    Correct.



    Correct in both counts, and I mentioned ths previously.

    Paul
    Thanks... just restating in my own words to make sure I understood you clearly.
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    Quote Originally Posted by pbender View Post
    Since this is inside an interlocking plant, turnout Y is definitely electrically interlocked with the signals. If it was not, an engine parked on the siding could be run onto the mainline even if turnout Z were lined for NS.
    That's why I said turnout Y was most likely NOT equipped with an electric lock; trains/engines would NOT be allowed to clear the main track into the industry spur in order to prevent the above scenario from happening (a train/engine heading south from the industry spur onto the main with turnout Z reversed). Turnout Y would be connected to the signal system in order to drop signals A, B, and D to Stop when it's reversed; but because it's located within the interlocking limits trains and engines would be prohibited from restoring the switch normal and reporting "in the clear" of the main track.


    Quote Originally Posted by pbender View Post
    The aspect CSX signal A can display depends on what signal C displays. What signal C displays is dependent on the position of crossover V.

    Paul
    ...and turnout X.

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    Quote Originally Posted by SooLineRob View Post
    That's why I said turnout Y was most likely NOT equipped with an electric lock; trains/engines would NOT be allowed to clear the main track into the industry spur in order to prevent the above scenario from happening (a train/engine heading south from the industry spur onto the main with turnout Z reversed). Turnout Y would be connected to the signal system in order to drop signals A, B, and D to Stop when it's reversed; but because it's located within the interlocking limits trains and engines would be prohibited from restoring the switch normal and reporting "in the clear" of the main track.
    All turnouts in signalled territory are connected to the signal system in that if a turnout in a block is thrown, it causes a short circuit. This short circuit is the trigger for a block to show occupied ( equipment wheels also cause the block to be occupied because they short circuit the track ).

    Now, if the turnout Y is thrown for the industrial siding, signal A will show at best a restricting signal to indicate the track is not signalled.

    In practice, electronic locks are installed on any manual turnouts within interlocking limits for several reasons. As stated earlier, a train* may occupy the siding for switching work or so the dispatcher can get it out ofthe way. The electronic lock will also be in place to prevent the position of the turnout from changing under a train ( which also forces the train crew to be a certain distance from the turnout before changing the switch position ). The operator ( or dispatcher ) may also have control over when the switch is unlocked, to force crews to keep him informed of the crews actions.

    *A train is defined by the rulebook as one or more engines with or without cars displaying markers.

    Paul
    Last edited by pbender; 11th Mar 2012 at 12:50 PM.

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    Quote Originally Posted by TwinDad View Post
    A particular combination of heads colored a certain way - say, yellow over red over green - is an Indication. Each possible Indication shows an Aspect, which is (loosely speaking) a rule the engineer should follow
    Correction: What the engineer/conductor see is the ASPECT, not the indication. The information the aspect conveys is the INDICATION. The indication is what the crew must follow per the operating rule.

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    Quote Originally Posted by pbender View Post
    Ok, what you actually have is a junction. in the U.S., most junctions are signalled with speed signalling.
    It's pretty safe to say that speed signaling pertains to almost all junctions in the U.S., and for that matter almost all signaling in the U.S. Won't rule it out, but I've yet to encounter route signaling anywhere here.

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    Quote Originally Posted by REM37411 View Post
    Can anyone enlighten me or point me in the right direction of a link to somewhere that will explain, hopefully in detail, modern railroad signals?


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    Quote Originally Posted by pbender View Post
    Turning the signals 90 degrees is actually required, either by rule or by law.
    Hate to be a pedant, but that's not correct: Signal heads can either be turned 90 degrees away form the track, or bagged to hide the lenses, or both. A particular railroad might have a standing rule regarding pre-cutover installations, and there may be state laws, but there is no federal law requiring that.

    I've installed many, many plants and done many, many cutovers in Washington and Oregon. We only bagged the signal heads.

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    Quote Originally Posted by pbender View Post
    The signal systems communicate through the rails and/or through seperate code lines. These are vital circuits with a fail safe requirement on the prototype. All of the information is concerned with occupancy ( occupied in this case is actually triggered by either a short circuit ( when equipment is in a block ) or an open circuit ( due to a break in the rail or an open switch )).
    It's not an absolute short circuit. The nominal resistive value of what we call a "shunt" is .06 Ohms and it's a federal law. All cars and locomotive are to have that nominal Ohmic value. The shunts we use in the field to test track circuits and crossing island circuits are also rated at .06 Ohms. We also have a "hardwire" option, but it is used only to determine linearity for grade crossing approaches when calculating lumped impedance adjustment values.

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