i’d like a better understanding of signals. My understanding is signals are not standard between railroad and maybe not even within the same railroad because of different vintage signal equipment. And my understanding is signal may have different purpose such as speed vs occupancy. I’m not interested in specific differences between railroad.
when I operate on the Pacific Southern, i generally interpret anything other than a stop signal as ok to go.
I’m hopeing more knowledgable peope can provide a comprehensive explaination of the purpose(s) of signals. I think you can think of them as indicating speed of operation depending on both occupancy of blocks ahead, condition of track, presence of turnouts and whether turnout is straight or diverging. on the other hand, they could be just indicating block occuopancy.
i’m not so interested in what the color/position of particular aspect is, but why particular aspect are indicated
Yes, most signals are specific to each railroad with certain aspects having different meanings as to whether being lit solid or flashing. Signals having two heads (beware of Politicians with two heads), are interlocking home signals controlled by a dispatcher. The upper head indicates the condition of the block ahead and the lower head indicates the route aligned at a switch. A signal with a single head is an automatic signal controlled by train movements. Stick with Green, Yellow and Red aspects. There’s a series of videos on youtube on how to read signals on CSX lines. A yellow signal would mean procede at restricted speed and be prepared to stop at the next signal which will be Red. Yellow or green aspects speed meanings would be dependent on the speed allowed by the tracks conditions, not only by the location of a preceding train.
Yup. Signals and interlockings are of particular facination to the LION.
BLOCK signals are automatic. HOME or INTERLOCKING signals are controlled by a dispatcher or by the interlocking tower.
The normal aspect on a BLOCK signal is GREEN, the normal aspect on a HOME signal is RED.
On the NYCT, where signals are only a few hundred feet apart:
RED = STOP : The Block ahead is occupied
YELLOW = Restricting : The next signal will be red.
GREEN = CLEAR : The next signal is not red.
On the subway, the RED signal is absolute and trains must stop, out on the railroads a RED signal usually means Stop and proceed with the intention of stoping with half the distince to an obstruction. Usually this is displayed as a Red signal with a Signal number on a placard, that placard is part of the aspect. If that placard is not there, then the signal is absolute.
The Block signals assume that one train is following another. A HOME signal will allow you to enter that track, and would be red if that track had approaching traffic running on it.
I will tell more, but it is time for morning prayer.
Also, don’t confuse the type of signal with the indication. That is, “Clear” means “Clear” whether it’s shown by a green light or a semaphore or high ball or whatever. Signal indications are pretty standard across the industry.
For block signals, Stop (red light) means the block ahead is occupied. Caution (yellow) means the block ahead is clear, but the following block is occupied, so be prepared for a possible Stop indication at the next signal. Clear (green) means the next two blocks are clear.
For interlocking signals, when approaching a turnout where a secondary line branches off from the mainline, you’ll see two heads, one above the other. Green-over-red means you’re continuing on the main; red-over-green means you’re going on the branchline. Red-over-red means the block ahead is occupied.
One thing that can be confusing is that on real railroads, stop/red is sometimes “permissive”, meaning you can go past some stop signals (usually at reduced speed) but some are “absolute” stops where you have to stop. That’s why railroads sometimes will add a second “dummy” stop/red signal to a single-head signal, to make clear it’s an “absolute” (red-over-red) stop. For example, where two lines merge into one, or one line crosses another, you may see both signals on the lines having a dummy head and a regular one. That way, an engineer can’t get confused and mistake the two-head interlocking signal for a one-headed block signal, which could be permissive. Where two lines cross or merge, only one train can have the right of way!
And just to confuse your wonderful explantion more, on the PRR single color positon light signals, a horizontal aspect indicates STOP, but an iluminated light below the signal head is permissive to continue, knowing that there is equipment in the block in front of you.
On LIRR and “equipment train” refers to the movement of an empty passenger train to a different terminal for use there. You would call it a dead-head move, LIRR calls it an “equipment train”, where as a work train with work equipment onit is simply called a work train.
Well to make a short story long, an equipment train was in a collision with an sutomobile out in Sofflk County, and the railroad correctly rep[orted that an equipment train was involved. Reporters daft and as stoupid as can be reported as a work tran, and why was a work train running at 80 miles per hour anyway.
I’ve had an interest in signals for a long time and have wanted an operating system on my layout. I became familiar with NORAC rules and signal indications when I was a locomotive electrician for Conrail and part of that job was to do required inspections, servicing, and testing on cab signals. I still have my rule book which includes a complete NORAC section. Now living in northern Nevada and amidst the UP system, there is a noticable difference. Here it’s mostly single track and UP uses diverge and flashing signals NORAC does not. I’m posting a signal chart for the NORAC signals.
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You can more info on this by doing a NORAC search.
A proper answer could take a book. Basically a signal system conveys information on how a train should proceed past that signal. The colors and arrangements of the lights are different but the intent of the signals are remarkably similar between all systems because they pretty much all do the same thing. You are correct that there is one stop signal and all other signals are some version of a proceed signal. One of the biggest differentiations is whether you are modeling manual block, automatic block, CTC or interlocking signals. Each of them have their own physical characteristics and types of operations. For example, ABS signals were the most common signals up until the 1970’s or so, but they really offer little or no advantage to a modeler (until the modeler reaches an era of caboose less operations).
If a signal has a number sign on it it is usually a permisive signal. IE stop and proceede at restricted speed. Among other uses they are used for spacing of trains. If you roll thru a permissive signal you are often ok. If you roll thru an absolute signal oftentimes you win a free vacation, however with no pay.
Oop. My bad. Just realized you were not really looking for a visual of signal indications. Well maybe it’ll be helpful anyway.
As I 've come to understand signals…more form the perspective of Norac and working on cab signals. That signals indicate the speed a train should be entering the block that a particular signal is displaying for. Example: If the engineer sees a signal red/green/red (medium clear) says to pass the signal at medium speed instead of track speed for clear, this could be an indicator that the next signal may have a less favorable indication. A yellow indication, yellow/red/red…for approach, indicates to pass the signal at 20mph (IIRC) being prepared for a full stop at the next signal. Yellow/green/red for approach medium says pass at 30 mph being ready for a possibly less favorable indication at the next signal.
In a nutshell, here in the states, signals govern train speed and warn of track/block conditions ahead.
I hope this better fits what you were asking initially.
In most block signal systems there absolute and permissive signals. Permissive signals can’t display a stop signal. There are two different ways they are differentiated. On some roads the Absolute signals have an “A” sign on the mast, on some they are the signals without a number plate.
The key is they are signals that display a stop indication. And by the way there is no such thing as “absolute stop”, there are absolute signals, but there isn’t an “absolute” stop indication, its just plain old stop. How you get by a stop indication depends on the era, signal system and what is happening beyond the signal.
Trains take a long time to stop, so the engineer needs a warning if he is going to be stopping. One of the purposes of intermediate signals is to provide that warning. In signal systems on territories with higher speeds (over 50 mph or so) they often have a get ready, get set, stop arrangement. The train will get a signal telling it to reduce speed to something around 40 mph, then the next signal will tell it to reduce to 30 mph and be prepared to stop at the next signal (approach). That gives the engineer typically more than 4 miles to reduce his speed where he can safely stop. If there is a situation where the engineer may have to stop more quickly, the signal system gives a slow, restricted or stop and proceed signal that gets the train down to 20 mph or less where the engineer can get stopped quickly.
This also points out the difference between the subway system signals described by LION and the signal systems used by freight railroads. The distances between signals are so short on a subway, that the requirement for a “yellow”, approach, signal is restricted speed while on freight railroads it will mean reduce speed to 30 mph and prepare to stop at the next signal (and that description is pretty much universal for all freight railroad si
One of the key concepts is the difference between ABS (automatic block system, and its sister APB automatic progressive block) and CTC (centralized traffic control.) the two different systems do different things and the signals are placed differently. CTC is an ABS system with certain switches and signals controlled by the dispatcher (or control operator).
In ABS the railroad is divided into “blocks”, typically track between sidings or junctions, and the main track at sidings (a siding is a location where trains may be met or passed). The signals control how fast the trains proceed and the manner in which they proceed into and through the next block, but don’t give authority to use the main track. The authority to use the main track is dependent on the timetable schedule, train orders, track warrants or other authority. If I pull up to the end of a siding in ABS territory and there is a green leaving signal, that doesn’t mean I can leave. I still have to have authority beyond the signal (running order, warrant, schedule), I have to make sure there are no superior trains due or overdue, that no other train has a rights over me or I have no waiting, meet or passing orders that apply.
In CTC, a proceed signal is the authority to use the main track (or verbal authority of the dispatcher or control operator). In CTC the signal superseded the superiority of trains (but not schedule times). So in CTC if I get to the end of a siding and it dis
The Railroad - What is is, What it Does by model railroading dean, John Armstrong, devotes an entire chapter to “Signals and Communications” including diagrams in every chapter’s subject. The neat thing about this book is how it answers questions you forgot to ask because you never knew the questions to ask.
i’ve read many of the books and websites mentioned. But I was looking for the kinds of explanations Dave H provided. Thanks you Dave for both responses.
seems to me, proper signals try to keep a train moving, even if slowly, to avoid ever coming to stop as well as maintaining a safe speed.
NORAC covers only the railroads listed, most of whom are Northeastern carriers. Most Western roads use some form of the General Code of Operating Rules, usually known as GCOR. NORAC is speed signaling, while GCOR is route signaling - the NORAC signals are typically associated with a specific speed (e.g., “approach limited” would require you to slow to limited speed (45mph), prepared to stop at the next signal, while GCOR would call a signal something like “approach diverging,” meanin, “proceed at a speed that’s safe for movement onto a diverging route,” which the engineer would be expected to know if he was qualified on that route.
I’m not qualified on any of them, but the CSX and NS rule books conform pretty closely to NORAC, BNSF conforms pretty closely to GCOR (as, I think, UP does). In any case, the Employee Timetable would typically specify which rule book is in effect, which is important, particularly in a place like Chicago. You can find both GCOR and NORAC online; they’re full of i
Technically the signal rules are railroad specific and not part of either GCOR or NORAC.
Actually approach limited in NORAC says to proceed approaching the next signal at limited speed. That is basically the same as approach limited.
NORAC will have more complicated signals since it covers railroads that operate at very high speeds, over 100 mph.
The PRR had rules that were somewhat different from the “typical” rules so any rule book that incorporates ex-PRR territory and rules will be different from the GCOR style rules.
Yes and no. The NORAC book states “these rules govern the operation of the railroads listed on the previous pages.” There is, for example, no specific Amtrak rulebook that governs the Northeast Corridor; NORAC does, and with other rules and instructions, as applicable, set by the employee timetable or other instructions or orders. If you look at an NS rulebook, it’s basically the NORAC rulebook, right down to the rule numbers (251 and 261, for example, are identical). A lot of the rules are dictated by the technology in service, and so the NS CSS rules are, IIRC, basically identical to the NORAC CSS rules because they govern the operation of the old five aspect cab signal system. FRA requires cab signals and/or automatic train stop for any operation over 79mph, and for speeds over 125mph, positive train control, which has its own set of rules (interestingly enough, not included in the basic NORAC book).
The NORAC rules descend, if that’s the way to put it, from the old Conrail rules, which were themselves a congeries of the rulebooks and signal systems of previous carriers. IIRC, NORAC started around 1983, about the time Conrail spun off the commuters. Companies like NS and CSX adopted the NORAC system, but the signal rules make an interesting comparison, because they include signals for predecessor systems outside the Northeast, that show some variations based on the practice of the companies that originally owned the routes. GCOR works in a similar way to NORAC, with each participating company having a vote in the adoption of new rules and editions.
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