Western Railroad Discussion > What determines signal aspect?

What criteria determines what combination of colors will be displayed at a particular interlocker/junction?

I've noticed in some interlockers that there will be 2 headed signals, 3 headed signals, or heads that display only 2 aspects along with heads that display 4 aspects.

Surely in the bureaucracy of railroads there are some sort of standard or rules that says, for example: "This route will be govered by a diverging approach slow" or "At this type switch a diverging clear limited will be displayed."

If I won the lottery I could sit trackside day and night and observe the various comings and goings to figure this out....

Any help is appreciated.

Thanks,
Alan

You know about route signalling vs speed signalling?

In the former, you'd only need a three-head signal if there were three (or more) possible routes past the signal. But in speed-signal territory a 15 or 20 mph switch will probably involve a red-over-red-over-green signal, even if there are only two possible routes over the switch.

Are we talking heads, or lights in a head? Standard light heads have tri color lights, one each red, yellow, and green. In a situation where a yellow might be the most positive color any train will ever see, a two light can and is used. The second head would be for the main diverging line, usually a siding, or a branch. Now, add a branch and a siding coming off at the same spot, and you add a third head. The top will always be the main line. The second for the siding or branch. When there is three, they are in descending order of use. The one that is lit with a permissive color tells the crew where they are going. Top is down the main, second is into the siding or branch, and third, if there, down the branch.

A search light signal has only one visible light, but internal mechanisms alllow the color seen to change. Other than that, it is all the same as above.

And your right, if you had won the lottery and could sit at an interlocker, you could figure out what the lights lead to.

KK

KoloradoKid Wrote:
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> Are we talking heads, or lights in a head?
> Standard light heads have tri color lights, one
> each red, yellow, and green. In a situation where
> a yellow might be the most positive color any
> train will ever see, a two light can and is used.
> The second head would be for the main diverging
> line, usually a siding, or a branch. Now, add a
> branch and a siding coming off at the same spot,
> and you add a third head. The top will always be
> the main line. The second for the siding or
> branch. When there is three, they are in
> descending order of use. The one that is lit with
> a permissive color tells the crew where they are
> going. Top is down the main, second is into the
> siding or branch, and third, if there, down the
> branch.
>
> A search light signal has only one visible light,
> but internal mechanisms alllow the color seen to
> change. Other than that, it is all the same as
> above.
>
> And your right, if you had won the lottery and
> could sit at an interlocker, you could figure out
> what the lights lead to.
>
> KK

A handy thing for speed signals that works with most indications is this: Red is a restricted speed.....yellow is medium speed and green is hi speed. ANY signal COULD be three lights but sometimes one or two lights is not necessary. But Top light is the slow speed route middle light is the medium speed route, and lower light is the hi speed route. SO, top red, middle green, lower red....Slow speed route not availalable, medium speed route is available for two blocks, hi speed route not available. The name is Medium Clear from the fact that only the medium route is available.
You can devine any other color light signal (speed based) from this plan except Approach Slow (yellow/yellow)also called Advance Approach. Restricting also doesn't follow the formula. But it's a know nothing signal only permitting passage, but not guaranteeing a clear block. Also, knowing this formula you can look at any color light signal and guesstimate where the train approaching same might go, and how far before he must diverge or stop. In fact directional signals give the same information, but the jargon is different. Approach Medium becomes Approach Diverging. Etc etc.

RED means STOP! Red over yellow is for "Restricted Speed."
But depending on what RR Rule Book you have, there are varations on every signal.
The Timetable may have "Special Instructions" for even a RED signal.
I wish some of you guys would "Shut up" if you don't have a clue what you are talking about.
The best thing to do is try to obtain a copy of the "Book of Operating Rules" for the RR you are interested in. If this is not possible, any old rule book would be better than nothing and at least give you an idea what the signals mean. You may find the signal rules in most Time Tables also.
Good luck,
gtr

I hope gtr is talking about johnnycando. This response was clear as MUD.

KK

Go to this link, it should help with some of the confusion, a little oudated but you'll get the idea. Very general and speeds vary from RR to RR

http://www.lundsten.dk/us_signaling/aspects_sp1996

gtirr Wrote:
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> RED means STOP! Red over yellow is for "Restricted
> Speed."
> But depending on what RR Rule Book you have, there
> are varations on every signal.
> The Timetable may have "Special Instructions" for
> even a RED signal.
> I wish some of you guys would "Shut up" if you
> don't have a clue what you are talking about.
> The best thing to do is try to obtain a copy of
> the "Book of Operating Rules" for the RR you are
> interested in. If this is not possible, any old
> rule book would be better than nothing and at
> least give you an idea what the signals mean. You
> may find the signal rules in most Time Tables
> also.
> Good luck,
> gtr

Yes, there are variations on signals. On the IC, red over yellow is a diverging approach.

GTI's post, while arrogant, hinted at a railroad-industry truth that is probably better for fans than it is for rails: different railroads -- and, thanks to mergers, different lines within the same company -- have different signal rules. As explained previously, the basic premises of green=go and red=stop are pretty much universal, but some of the more "detailed" signal aspects vary from road to road. Perhaps the most complex system is the former B&O color-position light signalling, which instead of using multiple-head aspects, employs an array of auxiliary lights that indicate medium or slow speed and/or diverging routes.

For the most part, the most complex signals are located at points where tracks diverge or converge, for obvious reasons. Out in the boondocks, you're more likely to see just a red-yellow-green system, though on heavily used lines with short signal blocks you may see a flashing yellow, yellow-over-yellow, or yellow-over-green aspect to create a second "advance" signal for a train to pass before it reaches a red. What you'll only rarely see is a signal head with just red and green -- the only situations common for those are controlled points on otherwise unsignalled lines (like railroad diamonds) or on a lower signal-head that, because its signal's situation, doesn't need a yellow lamp.

KoloradoKid Wrote:
-------------------------------------------------------
> Are we talking heads, or lights in a head?

Both. Here's an example:
The image shows a double track main, with crossover, and a siding. All signals have two heads. The aspects for each head is shown (eg. GYR-GYR is a 2-headed signal with 3 aspects on each head).

On the image, lets look at the crossover signal in the uppermost, right (the one that has a lunar aspect). When a train approaches it for the they could receive a GR, YR, RR, RG, RY, RL, YL, YY, YG, RR, plus any assortment of flashing aspects.

My question is: Is there any set rules that a railroad goes by to determine which route alignment will show which aspects?

(BTW, I've figured out the aspects for this interlocker ... by sitting trackside :)

> You know about route signalling vs speed
> signalling?

I haven't. How can you tell which is which?

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In the picture you show, I would expect to see the following under the CSX rules, which is what I'm most familiar with. Your local rules may vary, especially regarding the Y/Y and R/Y aspects.

G/R - Clear, straight thru on main track
Y/G - Approach medium, straight thru this location w/ diverging route at next signal or red at 2d signal
Y/Y - Approach slow, straight thru with red at 2d signal ahead or diverging route w/ slow speed at next signal
Y/R - Approach, straight thru w/ red at next signal
R/G - Crossover onto other main track, clear ahead
R/Y - Crossover onto other main track, red at next signal
R/L - Crossover onto uncontrolled siding, or any route into occupied block (Restricting aspect)
R/R - Stop

And this doesn't even begin to discuss what happens with flashing-light aspects

westexas Wrote:
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> What criteria determines what combination of
> colors will be displayed at a particular
> interlocker/junction?
The question can be read/answered a couple different ways. First, the number of possible indications is affected by the speed(s) that will govern used routes, and what block occupancy scenarios may be presented, and are both considerations when the track and signals are in the "Design" stage for a specific application. If the system was designed in the 1950's, there may have been considerable modifications to both the signal system and the track configuration since it's initial installation.
If you are asking how existing systems operate, the speed governing the routes that can be selected by the Dispatcher AND block occupancy conditions ahead of the train, are the primary factors in what causes a particular aspect to display under a specific condition(which is basically a restatement of the first part). This will also help to explain why, when you are sitting at a specific location and looking at a signal indication, it may change or "Upgrade" to a more favorable indication, as trains ahead move past signals located further away, or as the DS makes decisions to move trains further ahead when there is no conflicting traffic. Dispatcher's "machines" often have a "Fleet" function which means they can allow trains to follow one another without constantly watching over the progress of one train and lining signals for the following movement. Needless to say it can be very complex.
> I've noticed in some interlockers that there will
> be 2 headed signals, 3 headed signals, or heads
> that display only 2 aspects along with heads that
> display 4 aspects.
The speed for the routes selected can vary. A number of interlockings have crossovers that can be negotiated at a "Limited" speed, while these same signals may govern the entrance to a "Medium" or "Slow" speed siding. In any event, there must be a way to communicate these distinctions to the crew operating the train, and as just about everyone has noted above, the signal rules for the signals that are displayed is the typical field method. With multiple heads on the signals, more and varied indications can be displayed conveying that information, if the options are limited in the particular interlocking(i.e. no siding, etc.) then the number of aspects that will be needing displayed generally decreases as well(hence fewer heads in the initial installation). Other methods to control speeds are, again as noted above, Timetable Instructions, and Bulletin Orders(that being the paperwork that the crew carries to notify them of special conditions on the particular subdivision or line they are operating on). The reconfiguration explanation applies here as well, in that some systems may have been designed to indicate a variety of speeds, but over time the need to display a higher/lower speed has changed by upgraping or downgrading physical plant conditions and thus modifying the number of aspects needing displayed. Even so it is uncommon for the RR to send someone out to remove a signal head because it won't be displaying that indication any longer, more likely the system is modified to no longer give the aspect, and the head itself will simply display a "red" light, which on a lower aspect of a 3 head more or less indicates be governed by the indication above or below(except of course all red, which is "Stop").
> Surely in the bureaucracy of railroads there are
> some sort of standard or rules that says, for
> example: "This route will be govered by a
> diverging approach slow" or "At this type switch a
> diverging clear limited will be displayed."
Yes on the bureaucracy, but as stated by others "Route Signalling" speeds are communicated via TT or other written authority, "Speed Signals" communicate directly by the aspect(coupled with the written Signal Rules)
> If I won the lottery I could sit trackside day and
> night and observe the various comings and goings
> to figure this out....
This method has not as yet worked for me, you may want to go the more direct RR Employment route ;')

I'd suggest looking at Al Krug's write up on signals as it is one of the better explanations I've seen.
http://www.vcn.com/~alkrug/rrfacts/signals/signals.htm

As he explains, for some RRs, signals convey both speed and routing. For others, speed is determined by the timetable and routing by the signals. UP and BNSF, for instance, use routing, while some east coast RRs use speed.

Despite what someone else posted, red doesn't always mean stop either.

At least for routing signaling, any given signal has to tell two things...what to do at this signal, and what to expect at the next signal. If you look at a rule book, you will see phrases that say things like "prepared to stop at next signal" which describe the actions to take before getting to that next signal.

bobs Wrote:
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> Despite what someone else posted, red doesn't
> always mean stop either.
>
This is true, although in the given example of an interlocking with crossovers it would be highly unusual, to say the least, for an all-red to be a permissive (e.g., Stop and Proceed or Restricted Proceed) aspect. The way to distinguish between an "absolute" red and a "permissive" red is that the latter will have a number plate (or, in Canada where all signals have numbers, an "R" plate) to indicate that the signal is not absolute.

Whether a train must stop for a permissive signal, or merely slow to restricted speed, depends on the railroad's rule book. And railroads that normally require trains to stop for such signals will usually post "G" (for "grade") markers on uphill territory to indicate an exception, in consideration of the risk that an uphill train may have trouble starting again if it stops.

"Restricted speed," by the way, is typically the speed at which a train could be stopped short of a train ahead or other obstruction within half the distance of the line of sight, and normally not exceeding 15 mph.

General Code of Operating Rules (GCOR), not exceeding twenty (20) miles per hour when required to operate at restricted speed. Jesus H. Christ, can we make things difficult or what?!?

gladhand Wrote:
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> General Code of Operating Rules (GCOR), not
> exceeding twenty (20) miles per hour when required
> to operate at restricted speed. Jesus H. Christ,
> can we make things difficult or what?!?


What is difficult?

RE speed signalling vs route signalling, in extremely simple terms:
Speed signalling tells the engineer how fast he should be going, but not necessarily which route he will be taking (especially at complex interlockings).
Route signalling tells the engineer which route he'll be taking but not the speed over that route (he is expected to know the road).

Route signalling involves using route indicators to tell the driver which way he is going. In the UK these are feathers (5 lunar lights in a row) or theatre boxes (dot matrix displays). Splitting distants are also used, which are two heads side by side, one slightly lower than the other. http://www.davros.org/rail/signalling/articles/ has more info.

Also of interest: http://www.trainweb.org/railwaytechnical/sigind.html

Geoff M.

geoffm Wrote:
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>
> Route signalling involves using route indicators
> to tell the driver which way he is going. In the
> UK these are feathers (5 lunar lights in a row) or
> theatre boxes (dot matrix displays).

The only place I've seen similar displays in the U.S. was on the New York Central's line out of Grand Central in the Bronx. There were little boxes atop a signal bridge approaching Woodlawn Junction that had small lunar-white arrows indicating whether a train was lined for the Harlem Line or the New Haven. This knowledge was critical because a Harlem Line train sent the wrong way would quickly have run out of third rail from which to draw electric power. This was before the NH Line third rail was extended through Mount Vernon; I suspect those indicators were removed when the wayside signals were removed.

updispr Wrote:
-------------------------------------------------------
> gladhand Wrote:
> --------------------------------------------------
> -----
> > General Code of Operating Rules (GCOR), not
> > exceeding twenty (20) miles per hour when
> required
> > to operate at restricted speed. Jesus H.
> Christ,
> > can we make things difficult or what?!?
>
>
> What is difficult?

Nothing actually. My point was that there are different railroads, different rule-books, different procedures. Seems as though we sometimes try to "complicate" rules & make them more difficult than they really are.

gladhand Wrote:
--------------------------------------------------
> Nothing actually. My point was that there are
> different railroads, different rule-books,
> different procedures. Seems as though we sometimes
> try to "complicate" rules & make them more
> difficult than they really are.

Would be kind of nice if we all carried 1 book of Rules though, wouldn't it.