Perry BabinIt received a yellow on the bottom head and didn't move. Why didn't it move? It then received a green on the bottom head and began to move.
The camera is pointed SW and the signal is at
https://goo.gl/maps/dUawVDHy2afXXLXe7
Another look https://goo.gl/maps/W35K9xUGXpoHGwGMA
First guess about the automatic crossing gates: they come down as the train approaches, but when the train stops short of the xing the gates will eventually rise. Dunno how the gates figure out that the train has started to move; maybe there's a trackside microphone so the engineer can sound the horn to re-lower the gates?
I know nothing about Waycross. If this train saw red over red over green, we can assume the next signal ahead is yellow or green, but he's probably not supposed to exceed 15-20 miles/hour for now.
By the way: in the US, "depot" means station building; that trackage ahead of the train is called the yard, except there probably is a track, called the main, that passes around the yard. If a train is headed for the main, maybe it will get a green on the top head of the signal. And maybe no such train has appeared for you. But you're looking down CSX's main line from the Northeast to Florida, so there must be a thru track that avoids the yard, and that's what the top head of the signal is for.
(I see now that the Folkston Cutoff still exists; no idea how many CSX freights use it instead of going thru Waycross.)
I was going to delete this but don't see the option. If it can't be deleted, you can see (barely) that the bottom head went from red to lunar then back to red. When it went back to red, the middle head went from red to green. This train was switched to the track that went to the right.
Does anyone know why they have all of the green lights in the railyard?
It depends on circumstances why trains don't move, but instead wait for a more favorable indication. With a yellow, you would expect the next signal to be more restrictive, either a stop, stop and proceed, or a restricting. Waiting for the green means you won't have to stop or proceed at restricted speed into a possibly occupied block. Often taking the yellow could mean having to stop on crossings at the next signal for who knows how long. (Yes, we do try to avoid blocking crossings, or at least if we must, block the less important ones.) Waiting for the green, even when you have the Advance Approach before the yellow, means you have a little bit of room to run. In terminal situations it might not be much, but if you are out in the open, letting the guy ahead get some room for you may mean not having to slow down at every signal because you're catching up.
Most modern crossing circuits detect when movement begins. Many you can stop within a car length and the gates will time out and raise. When you begin to move, the circuitry senses the movement and activates the signals and gate. It can be a pain when circumstances require such a close stop and then beginning movement and waiting for the signals to activate. Usually such things happen when switching or setting out and picking up.
I had an unusual signal yesterday. They moved a block signal about a quarter mile, using a new signal. The signal is in advance of a 60 mph turnout. Usually, even when the signal governing the turnout is at approach or approach diverging, the old advance signal would give an advance approach indication. (For us, that's a flashing yellow over red on the old signal.)
Instead, the signal was a yellow over flashing red or Approach Restricting for us. PTC didn't indicate that the next signal was a Restricting nor that it was going to require restricted speed at the next signal. I was prepared for it anyway. We were going to stop at the depot about a quarter mile past the turnout anyway. It's not our normal change out point, but one for the long pool. Us short poolers usually go another 38 miles for our normal change out, but we only had about 10 minutes left to work.
PTC has really helped that you can "see" ahead of you. It indicates "targets" signals, speed restrictions, etc. 6 miles ahead, although the screen only actually shows about 5 miles ahead.
It helped me today to avoid blocking crossings, Some that have no other way in/out other than the crossings. We have a few places at my home terminal where we can change crews. The dispatcher never gave us any instructions as to where to change out. PTC started showing on the fringe that we were probably going to go into the siding. Once the actual control point controlling the route into the siding was on the screen, we weren't lined up past the signal. I immediately had time to take action to bring the train to a safe stop at the first change out point. Had I had to actually wait to see the wayside signals to figure out what was going on, I would've blocked half the town and some of those only access crossings.
Jeff
Assuming that these are single color lights (not searchlight type signals), how does it work with only one head (only for high speed indication?)?
The signal tower to the left of the untitled placemark is the signal tower (for reference to the track configuration).
Perry BabinAssuming that these are single color lights (not searchlight type signals), how does it work with only one head (only for high speed indication?)?
That signal (its counterpart on UP is just below the diamond) is chiefly there to protect the diamond. You can see one BNSF signal tower alongside the rail park. The other is out of sight at the bottom of the image.
The Rochelle diamond is automatic - first come, first served. As such the UP and BNSF signals are interconnected (ie, interlocked). Occasionally, you'll see a train on one of the lines dawdle a bit in order to hold the diamond for another train on their line.
Since there is no routing to be done at this point, only one head is needed. Given a green signal (ie, it's OK to cross the diamond) trains can proceed at timetable speed. Remember that the other two signals in the stack are considered red, as they are not there.
The signals will also be tied into the regular lineside signals so they can convey the usual information about signals further down the line.
An interesting tidbit about Rochelle - although the diamond is 2x2 tracks, one of the BNSF tracks is, in effect, a long passing siding, beginning a few miles south of Rochelle and ending a few miles NW of the diamond (or vice versa, if you like).
Corrections gladly accepted!
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
If you zoom in on the aerials of Rochelle
https://goo.gl/maps/MfJqLEg7Q6jpsSKx5
you can see there are no crossovers in the neighborhood (on UP anyway). A train on the UP approaching the crossing knows its route ahead is straight, with no need to slow down, assuming no trains ahead. A single green signal tells the engineer no trains are ahead -- no need for more info.
Shouldn't there be a sign with the letter "A" for absolute if the signal is for the diamond. I don't see that, or a signal number which would indicate a block signal. In the era of PTC, is there no longer signage on signals?
MidlandMikeShouldn't there be a sign with the letter "A" for absolute if the signal is for the diamond. I don't see that, or a signal number which would indicate a block signal. In the era of PTC, is there no longer signage on signals?
Most railroad rule books define an Absolute Signal as a signal without Number Plate. Signals with Number Plates are defined as Intermediate Signals. The most restrictive indication that an Absolute Signal can display is STOP. The most restrictive indication a Intermediat Signal can display is Restricting.
Back in the past, what is now known as Restricting on some carriers was known as 'Stop & Proceed'. A train size has grown, the carriers no longer want them to Stop and then Proceed at Restricted Speed - now Restricting permits the train to proceed at Restricted Speed without stopping.
Dispatcher or Control Operator's permission is required to pass an Absolute Stop Signal.
Never too old to have a happy childhood!
Other than in pictures, mostly from years past, I've never seen an "A" plate on an absolute signal. Just the absence of a number plate.
We have both "Restricting" and "Restricted Proceed" signals. The only difference is the Restricted Proceed is only on number plated signals. What, as already been referred to, is casually called an intermediate signal. There's no actual rule book definition of an intermediate, but everyone uses the term and knows what is being discussed.
There are, or maybe were - I only know about the one I deal with, four locations on the UP where you can crossover on the indication of a single head signal. One is in Omaha where the Falls City subdivision (up from Kansas City) joins the Omaha subdivision. Where they join, a train going east on Omaha #2 or Falls City #3 will receive a single yellow (approach) if they will continue beyond on Omaha #2. If a crossover move for either is lined to go to Omaha #1, the train will get a single lunar (restricting).
Until about 10 years ago, you could crossover on the yellow. The FRA made them change the aspects after a train that had been cleared through a Form B (work zone) only on #2 crossed over to #1. Back then, unless the dispatcher told you your route, you wouldn't know if you were going on #1 or #2 beyond that signal. They should've just replaced the signals with ones that could display a diverging aspect, but instead went the cheap route.
Now with PTC engaged, you can see what route you will be taking.
jeffhergertOther than in pictures, mostly from years past, I've never seen an "A" plate on an absolute signal. Just the absence of a number plate. We have both "Restricting" and "Restricted Proceed" signals. The only difference is the Restricted Proceed is only on number plated signals. What, as already been referred to, is casually called an intermediate signal. There's no actual rule book definition of an intermediate, but everyone uses the term and knows what is being discussed. There are, or maybe were - I only know about the one I deal with, four locations on the UP where you can crossover on the indication of a single head signal. One is in Omaha where the Falls City subdivision (up from Kansas City) joins the Omaha subdivision. Where they join, a train going east on Omaha #2 or Falls City #3 will receive a single yellow (approach) if they will continue beyond on Omaha #2. If a crossover move for either is lined to go to Omaha #1, the train will get a single lunar (restricting). Until about 10 years ago, you could crossover on the yellow. The FRA made them change the aspects after a train that had been cleared through a Form B (work zone) only on #2 crossed over to #1. Back then, unless the dispatcher told you your route, you wouldn't know if you were going on #1 or #2 beyond that signal. They should've just replaced the signals with ones that could display a diverging aspect, but instead went the cheap route. Now with PTC engaged, you can see what route you will be taking. Jeff
Back in the day of double track being operated under current of traffic signaling Rules 251-252 the B&O at many tower locations had directional passing sidings, some were signaled and some were not. When lining a train into a unsignaled siding, the interlocking signal would display Restricting, the same indication that would be displayed when the train was being reversed against the current of traffic for its direction (when operating against the current of traffic the track IS NOT SIGNALED). The only indication that would tell the train the route, was the display of the Train Order Signal as the train required Train Order authority to operate against the current of traffic.
At this point in time most crossover and switches into passing sidings were all 10 MPH.
MidlandMikeShouldn't there be a sign with the letter "A" for absolute if the signal is for the diamond.
Offhand guess: on any US railroad, "A" meant a dispatcher controlled signal, not a locally controlled signal. But many? most? RRs didn't bother with A's at all.
timzOffhand guess: on any US railroad, "A" meant a dispatcher controlled signal, not a locally controlled signal. But many? most? RRs didn't bother with A's at all.
Not in the northeast. Only signals to have As on them were "approach restricting/approach clear" signals. Normally used when going from dark to signalled territory.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
Railroad signal lights convey essential information: red means stop, green means clear to proceed, yellow signals caution, and flashing red indicates trains must stop. Additionally, flashing yellow signals an approach with caution, lunar white acts as a backup, and double red at a grade crossing warns of an approaching train.
Oh wow, lots of replies here that it didn't tell me about. Ooops.
The signal changed from showing Restricting to showing Medium Clear. This area is pretty complicated, as it has two separate interlockings abutting each other (CP Rice, and CP Waycross Jct). Trains heading RIGHT here onto the Fitzgerald sub have to get switched through both interlcokings. The boundary on that connector track is a bi-directional absolute signal that protects both control points. It is only 1000 feet beyond the signal in the video, so this signal shows Restricting when that next signal shows Stop. Once that next signal is able to upgrade to Medium Clear or Medium Approach, this signal upgrades to Medium Clear. That is why there is no Yellow lamp on the second head—it's not needed. I do have a description of how this signal works on my short main signals page.
There's no reason for anyting other than the red on top because there will be no track speed at this location. << ?
And, yes, that's why there is only Red on the top: Track speed indications are not possible here, but the Red must still be there for the Medium and Slow speed aspects.
Those are switch point position indicators. The important and often-used turnouts in a big yard throat like this are still operated manually or semi-manually, but are often given local remote control by radio so crews don't have to waste time to stop to change them all the time. The indicators show the state of the switch: Green for "closed" or Normal (straight ahead), Yellow for "open" or Reverse (diverging), and Red for Error/Not Locked/Not Ready. The yardmaster may have direct control over setting up paths through the throat, and/or train crews can key special DTMF (touch tone) codes on the radio to change the switches. This saves a lot of time, and fuel.
It received a yellow on the bottom head and didn't move. Why didn't it move?
The train wasn't ready to move, or was waiting for a better signal indication so it wouldn't have to move a few thousand feet and stop again, blocking this level crossing and maybe others.
It then received a green on the bottom head and began to move. At about the same time, the gates came down and it crossed the road. What controlled the gates? It seems like the train position couldn't be used since it was already at the crossing.
Why didn't the gates come down on yellow?
The wayside signaling has absolutely nothing to do with the level crossing signals. With the exception of overlapping wiring circuits, they are completely separate things.
Almost all US and Canadian level crossing signals are fully automatic. Most grade crossings that are used regularly these days have a grade crossing predictor installed. What this does is it puts a special pulsed circuit on the track in both directions. The predictor will listen to the "sound" of these pulses as they go down the rails. If a train is present and shorts-out the rails (which is how track circuits all work), the predictor will hear this short out, and it can tell how far away the train wheels are from the crossing. It can tell if the train is moving towards or away from the crossing, and how fast it is moving. The goal is constant warning time for signals at the level crossing so that they activate a desired number of seconds (usually set to 20–40) before the train arrives, no matter how fast the train is going. If the predictor detects that the train has stopped moving towards the crossing, it will, after a delay, "time out" and turn the crossing signals off. It will turn them back on when it detects the train is moving again. This is very valuable in spots like this where trains often stop all over the place.
Does the yellow mean that only one block ahead was clear?
Does the green on the bottom head indicate that the next two signal blocks are clear?
Yes and Yes.
MidlandMike Shouldn't there be a sign with the letter "A" for absolute if the signal is for the diamond. I don't see that, or a signal number which would indicate a block signal. In the era of PTC, is there no longer signage on signals?
Perry Babin The following site is basically what you posted but with different formatting. http://www.mikeroque.com/understanding-railroad-signals/
The following site is basically what you posted but with different formatting.
http://www.mikeroque.com/understanding-railroad-signals/
Yes, he has reposted portions of Mr. Krug's former webpages about signaling. It's the best explanaiton about "signals" that I've ever come across. If that doesn't make sense to you, feel free to ask questions.
Perry Babin As with most of railroading, some of my questions were answered here, others by searching. There are too many variations to have them all answered (or for me to know what all to ask). This goes for all of the rest of railroading. It's been evolving for a very long time so unless a very specific question is asked, the answer will likely be incomplete. Getting questions answered (for me) has been best if I have done enough research to have more than half of the answer. Then, I can be very specific and get an equally specific answer. This site has been very good. I also get answers from some YT channels.
As with most of railroading, some of my questions were answered here, others by searching. There are too many variations to have them all answered (or for me to know what all to ask).
This goes for all of the rest of railroading. It's been evolving for a very long time so unless a very specific question is asked, the answer will likely be incomplete. Getting questions answered (for me) has been best if I have done enough research to have more than half of the answer. Then, I can be very specific and get an equally specific answer. This site has been very good. I also get answers from some YT channels.
Signaling is a very complicated topic, especially in the United States. Personally, I find that envigorating, because the details fascinate me. As railfans, we're all always learners anyway. No one knows everything about railroading, not even the ones who are paid to do it.
Almost all US signaling system have some degree of roots in the basic system outlined by Mr. Krug. Some signal schemas have been more "corrupted" in that regard than others, but more often than not the differences are pretty minor.
Perry Babin For signals, I don't think I'll ever fully understand them. I think it would require posting photos of a specific signal on a track or set of parallel tracks and ask for all the possible signals and that's simply too much to ask. There are a lot of other things that interest me about railroading and I learn more each day.
For signals, I don't think I'll ever fully understand them. I think it would require posting photos of a specific signal on a track or set of parallel tracks and ask for all the possible signals and that's simply too much to ask. There are a lot of other things that interest me about railroading and I learn more each day.
Well, "fully understand" is pretty subjective. It depends on why you want to understand them. There are aspects of history, safety, mergers, technology, and operational efficiency to learn why signaling is the way it is. But, just learning what the signals in the areas you railfan can mean should be pretty straightforward. I don't know about you, but I like to know when a train is coming!
tree68 One thing I don't have down yet is the modifier that is a flashing head.
One thing I don't have down yet is the modifier that is a flashing head.
What is confusing about that to you? Is there a specific situation you don't understand? Or is it the philosophy of flashing in the grand scheme of things?
Jovet tree68 One thing I don't have down yet is the modifier that is a flashing head. What is confusing about that to you? Is there a specific situation you don't understand? Or is it the philosophy of flashing in the grand scheme of things?
On Dispatcher model board representations - the board only shows if a signal is (supposed) displayed - not the indication that the signal is displaying. The indication is controled by the ABS rules that are wired into signal systems. Depending upon route or track occupancy on the route lined, the indication displayed CAN be anything from Restricting to Clear and appropriate indications in between as dictated by the actual conditions and other train locations.
I don't think you should look at a flashing aspect as a modifier. It is just another signal aspect with it's own name and indication. Using a flashing indication allows more possible aspects and indications beyond the basic green, yellow and red colors. While color light signals might sometimes have a fourth color (lunar white) on a signal head, a searchlight type signal can only display three colors.
While searchlights are being replaced, they are still out there in some locations. The lunar aspect also seems to be falling out of favor on some roads. It's being replaced with a flashing red aspect.
When looking at a particular railroad's signal chart, it does look a bit intimidating. Two things to remember about the charts. One is that an employee most likely will not see all of the combinations available. Depending on where one works, you might only see the basic block signal aspects and indications. The other is that working a territory regularly, you get to know the signals you see every day. It's rare to come across a signal that you haven't seen before. When we have signal changes, a bulletin or general order is usually given if there is a major change in what the signal can display.
jeffhergertI don't think you should look at a flashing aspect as a modifier.
Flashing for NORAC and NORAC-similar "upgrades" the signal. But the term is used mostly as a way to learn/remember the aspects.
Red over green = medium clear. Red over flashing green = limited clear.
Trivia: PRR used flashing aspects with their PLs, but they also retained an option of using a yellow triangle sign on the signal that upgraded the signal without the flashing. Only ever saw it on one signal (long gone).
Jovet MidlandMike Shouldn't there be a sign with the letter "A" for absolute if the signal is for the diamond. I don't see that, or a signal number which would indicate a block signal. In the era of PTC, is there no longer signage on signals? It sounds like you're thinking of Canada and how they roll. That is not how things are done in the US.
No, I'm thinking of U.S. Maybe it's more of an eastern thing, or a 50 year old thing.
zugmann jeffhergert I don't think you should look at a flashing aspect as a modifier. Flashing for NORAC and NORAC-similar "upgrades" the signal. But the term is used mostly as a way to learn/remember the aspects. Red over green = medium clear. Red over flashing green = limited clear. Trivia: PRR used flashing aspects with their PLs, but they also retained an option of using a yellow triangle sign on the signal that upgraded the signal without the flashing. Only ever saw it on one signal (long gone).
jeffhergert I don't think you should look at a flashing aspect as a modifier.
I have been told that flashing aspects were used for limited speed applications for the purpose of safety. If the mechanism producing the on-off flash effect fails, then the signal will revert back to a less favorable aspect with an indication for medium speed. That is, it would "fail safe".
This principle seems to apply to most of the other non-limited speed flashing signal aspects that I have seen on different railroads too. For example, a flashing yellow Approach Diverging signal reverts back to a solid yellow Approach, a flashing Red Restricting signal would revert back to a solid red Stop, etc. It makes sense. Better for a train to stop or run slower than necessary than accidently tell it to run faster than what is safe. I do wonder, however, if it would be possible for a malfunctioning signal that is "pumping" to be accidentally interpreted from a distance as a more favorable limited speed aspect. The few "pumping" signals that I have personally observed looked like they were going nuts. Also, they were bouncing back and forth between Proceed and Stop aspects. That's definitely not right.
ns145 zugmann jeffhergert I don't think you should look at a flashing aspect as a modifier. Flashing for NORAC and NORAC-similar "upgrades" the signal. But the term is used mostly as a way to learn/remember the aspects. Red over green = medium clear. Red over flashing green = limited clear. Trivia: PRR used flashing aspects with their PLs, but they also retained an option of using a yellow triangle sign on the signal that upgraded the signal without the flashing. Only ever saw it on one signal (long gone). I have been told that flashing aspects were used for limited speed applications for the purpose of safety. If the mechanism producing the on-off flash effect fails, then the signal will revert back to a less favorable aspect with an indication for medium speed. That is, it would "fail safe". This principle seems to apply to most of the other non-limited speed flashing signal aspects that I have seen on different railroads too. For example, a flashing yellow Approach Diverging signal reverts back to a solid yellow Approach, a flashing Red Restricting signal would revert back to a solid red Stop, etc. It makes sense. Better for a train to stop or run slower than necessary than accidently tell it to run faster than what is safe. I do wonder, however, if it would be possible for a malfunctioning signal that is "pumping" to be accidentally interpreted from a distance as a more favorable limited speed aspect. The few "pumping" signals that I have personally observed looked like they were going nuts. Also, they were bouncing back and forth between Proceed and Stop aspects. That's definitely not right.
A crew that sees a signal that is 'pumping', by rule is expected to comply with the MOST RESTRICTIVE indication that the signal can display. Restricted at signals with a number plate and STOP at signals without a number plate.
Yes, I agree, assuming that they know that it's 'pumping'. My question was regarding the possibility of mis-interpretation. Think of a scenario with a single head signal where a red bulb is burned out and all the crew sees is the green bulb pulsing on and off as the signal switches between Proceed and Stop.
BaltACDOn Dispatcher model board representations - the board only shows if a signal is (supposed) displayed - not the indication that the signal is displaying. The indication is controled by the ABS rules that are wired into signal systems. Depending upon route or track occupancy on the route lined, the indication displayed CAN be anything from Restricting to Clear and appropriate indications in between as dictated by the actual conditions and other train locations.
Be careful throwing out "ABS" or "ABS rules" out there willy-nilly.
The usual term is track conditions. Despite CSX's idiotic pleas otherwise, there are not ABS signals in CTC territory (for example).
jeffhergertI don't think you should look at a flashing aspect as a modifier. It is just another signal aspect with it's own name and indication. Using a flashing indication allows more possible aspects and indications beyond the basic green, yellow and red colors.
But, that makes flashing versus steady a modifier. Steady is the more-common, so flashing is the modified variation. That modification is usually better than what it would be if it weren't flashing.
jeffhergertWhen looking at a particular railroad's signal chart, it does look a bit intimidating. Two things to remember about the charts. One is that an employee most likely will not see all of the combinations available. Depending on where one works, you might only see the basic block signal aspects and indications. The other is that working a territory regularly, you get to know the signals you see every day. It's rare to come across a signal that you haven't seen before. When we have signal changes, a bulletin or general order is usually given if there is a major change in what the signal can display.
I know I'm an idealist, but it's a shame that the philosophy of the singaling system isn't learnëd on more employees. Studying the details of a signal chart tells how you that signaling schema ticks.
ns145I have been told that flashing aspects were used for limited speed applications for the purpose of safety. If the mechanism producing the on-off flash effect fails, then the signal will revert back to a less favorable aspect with an indication for medium speed. That is, it would "fail safe". This principle seems to apply to most of the other non-limited speed flashing signal aspects that I have seen on different railroads too. For example, a flashing yellow Approach Diverging signal reverts back to a solid yellow Approach, a flashing Red Restricting signal would revert back to a solid red Stop, etc. It makes sense. Better for a train to stop or run slower than necessary than accidently tell it to run faster than what is safe.
This principle seems to apply to most of the other non-limited speed flashing signal aspects that I have seen on different railroads too. For example, a flashing yellow Approach Diverging signal reverts back to a solid yellow Approach, a flashing Red Restricting signal would revert back to a solid red Stop, etc. It makes sense. Better for a train to stop or run slower than necessary than accidently tell it to run faster than what is safe.
Just remember that flashing aspects can fail two ways: steady lit or steady dark.
The graceful and safe downgrade of a failed flashing aspect is definitely desired. It is not often that wrong-side failure is designed into a signal system, but it has happened. (Looking at you, N&W!)
JovetI know I'm an idealist, but it's a shame that the philosophy of the singaling system isn't learnëd on more employees. Studying the details of a signal chart tells how you that signaling schema ticks.
Fun for trivia nights and forums (or to bore a new conductor); pretty uselss for operations.
Jovet BaltACD On Dispatcher model board representations - the board only shows if a signal is (supposed) displayed - not the indication that the signal is displaying. The indication is controled by the ABS rules that are wired into signal systems. Depending upon route or track occupancy on the route lined, the indication displayed CAN be anything from Restricting to Clear and appropriate indications in between as dictated by the actual conditions and other train locations. Be careful throwing out "ABS" or "ABS rules" out there willy-nilly. The usual term is track conditions. Despite CSX's idiotic please otherwise, there are not ABS signals in CTC territory (for example).
BaltACD On Dispatcher model board representations - the board only shows if a signal is (supposed) displayed - not the indication that the signal is displaying. The indication is controled by the ABS rules that are wired into signal systems. Depending upon route or track occupancy on the route lined, the indication displayed CAN be anything from Restricting to Clear and appropriate indications in between as dictated by the actual conditions and other train locations.
The usual term is track conditions. Despite CSX's idiotic please otherwise, there are not ABS signals in CTC territory (for example).
ABS - Automatic Block Signals
CTC operates the Control Points - where switches and derails can route trains on multiple routes through the Control Point.
Signals between Control Points operate on Automatic Block Signal rules.
One other thing to remember - Today's Class 1's are operating, in many cases, with the LEGACY signal systems that existed on the 130+ Class 1 carriers that have been winnowed into becoming today's SIX major Class 1 carriers. BNSF CN CPKC CSX NS UP.
You learn what you need to do your job. If you're qualified on a territory, you'll know the signals you may see.
A fantastic example of this is B&O's CPLs.
A fully loaded CPL has eight lamps on the disk and six markers (3 above and three below). Fully loaded CPLs were rare (and even moreso now).
Instead, a given CPL only contains the lamps in the disk and the markers that are needed for a given location.
For example, the SE wye/transfer signal (for traffic going from WB to SB) only has one marker - the center bottom. That's because it can never show anything better than a medium clear or a medium approach.
The lunar that would occupy the upper left/lower right lamp locations in a CPL disk has been pretty much replaced. It would indicate restricting.
I usually tell folks that at its simplest, red is stop, yellow=approach, green=go. There are "always" three heads. If a head isn't there, it's the bottom (or bottom and middle), and is considered to be red. The top head is track speed, the center head is medium speed, and the bottom head is slow speed, all as defined in the rulebook.
Yes, there are all sorts of variations on the theme.
As Balt mentioned, one challenge these days is knowing which signal system you are operating under, as a given aspect may have different meanings on different railroads. This was the root cause of the Amtrak rear-ender some years ago in Indiana (or was it Illinois?), wherein the engineer essentially applied the wrong rulebook to a signal and ended up piling into the rear end of a freight.
BaltACD Jovet BaltACD On Dispatcher model board representations - the board only shows if a signal is (supposed) displayed - not the indication that the signal is displaying. The indication is controled by the ABS rules that are wired into signal systems. Depending upon route or track occupancy on the route lined, the indication displayed CAN be anything from Restricting to Clear and appropriate indications in between as dictated by the actual conditions and other train locations. Be careful throwing out "ABS" or "ABS rules" out there willy-nilly. The usual term is track conditions. Despite CSX's idiotic please otherwise, there are not ABS signals in CTC territory (for example). ABS - Automatic Block Signals CTC operates the Control Points - where switches and derails can route trains on multiple routes through the Control Point. Signals between Control Points operate on Automatic Block Signal rules. One other thing to remember - Today's Class 1's are operating, in many cases, with the LEGACY signal systems that existed on the 130+ Class 1 carriers that have been winnowed into becoming today's SIX major Class 1 carriers. BNSF CN CPKC CSX NS UP.
In the last 30 to 40 years, some rules or their applications have been (in effect) "dumbed down." Some things have been simplified to "this OR that" instead of "this AND that." I have some old ETTs that show ABS over the entire subdivision and then where CTC is in efffect on that same subdivision.
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