ROBERT PETRICK ATLANTIC CENTRAL On our model layouts we can simply make do with a limited number of aspects and only use interlocking or absolute signals in all cases. So, signals with one head, red = stop, yellow = approach prepare to stop at next signal, green = clear. In or about 1977, the entire Star Wars genre began with a simple declarative statement of fact: . . . a long time ago in a galaxy far, far away . . . Who doesn't love a place where the rules are clear cut and concise? Robert
ATLANTIC CENTRAL On our model layouts we can simply make do with a limited number of aspects and only use interlocking or absolute signals in all cases. So, signals with one head, red = stop, yellow = approach prepare to stop at next signal, green = clear.
On our model layouts we can simply make do with a limited number of aspects and only use interlocking or absolute signals in all cases.
So, signals with one head, red = stop, yellow = approach prepare to stop at next signal, green = clear.
In or about 1977, the entire Star Wars genre began with a simple declarative statement of fact: . . . a long time ago in a galaxy far, far away . . .
Who doesn't love a place where the rules are clear cut and concise?
Robert
Agreed, and the interesting thing is that the aspects I do use are pretty much correct for the situations and the era I model.
wjstix refered to Bruce Chubb and his early work on signals and operation, much of what I do is based on his work, as well as Paul Mallery and Ed Ravenscroft.
Too many people in this hobby today have failed to understand the idea of "selective compression", not just in physical size, but in complexity.
Sheldon
LINK to SNSR Blog
One other note, my simplified signals use even less aspects than I listed above.
Two and three head interlocking signals never show Yellow "approach" on the two upper heads. My blocks are long and with DC control the status of the block past the one you are entering is not important.
Secondly, in place of those "approach" aspects, there is a single head signal half way thru the block, it is an approach signal for the next interlocking and never shows "stop", it shows green when the next signal is green, and yellow when the next signal is red.
This provides more information while using fewer aspects for the operators to learn.
gregc it's clear to me that signals can be interpreted in different ways depending on era, RR and situation. my questions was what makes sense for model RRs who aren't trained to interpret the wide variety of possible signals or who may be unfamiliar with the unique situations on a particular layout. here in Cumberland, CSX has 3 headed south facing (compass) signals at the fairgrounds. the bottom signal indicates that the northbound train should stop before the access road to the fairgrounds. the top signal indicates that it is clear thru Viaduct Junction. but the middle signal indicates to stop at the bridge to avoid blocking city streets or for a possible crew change (note the woodend staircase between the track and road) i'm told there is a similar situation on the tracks from Pittsburgh leading into Cumberland. there's a crew change point at a billboard in the narrows. 2497
it's clear to me that signals can be interpreted in different ways depending on era, RR and situation.
my questions was what makes sense for model RRs who aren't trained to interpret the wide variety of possible signals or who may be unfamiliar with the unique situations on a particular layout.
here in Cumberland, CSX has 3 headed south facing (compass) signals at the fairgrounds. the bottom signal indicates that the northbound train should stop before the access road to the fairgrounds. the top signal indicates that it is clear thru Viaduct Junction. but the middle signal indicates to stop at the bridge to avoid blocking city streets or for a possible crew change (note the woodend staircase between the track and road)
i'm told there is a similar situation on the tracks from Pittsburgh leading into Cumberland. there's a crew change point at a billboard in the narrows.
2497
I have no thoughts on the prototype situation you describe, it has no bearing on what is practical for our model layouts.
Two heads assumes an interlocking, G/R = main route clear, Y/R = main route approach, R/G = diverging route clear at specified speed, R/Y = diverging route approach prepare to stop at next signal. R/R = stop.
Three heads assume a more complex interlocking. Aspects for top two heads apply, third head indicates more restrictive diverging route, R/R/Y = restricted speed route clear, R/R/R = stop. Third head will be red when either upper head shows other than red.
That is simple and all most layouts need.
Easy to learn, ALL RED = Stop, Green on top means clear for the main, everything else means slow down.
Forget the rest of the prototype aspects and rule books.
In "How to Operate Your Model Railroad" author Bruce Chubb had a good section on signalling. He said that for most model railroads, very simple signals (one head with two lights, two heads each with two lights, and one head/two light dwarfs) would really be all you need. He pointed out that making a rule that a single red light always means 'stop' (unlike the prototype where it can have different meanings) helped a lot to make things simpler.
I'd say too that to keep it simple, you would want to keep it consistent. Having say green means you're clear to proceed, red means stop, and yellow means you're turning off onto a side track or branchline or whatever, isn't perfectly prototypical, but could be a simple, easy way for people to understand what's going on.
greg - Philadelphia & Reading / Reading
BTW if you go about 5 minutes into the NYC film, it explains their two-head (in this case, semaphores) block signaling, where having two heads allows for four indications instead of the usual three for block signaling.
cv_acr gregc it's not clear to me how signals indicate route. Any indication that has "Diverging" or a speed indicated in it, implies a different route being taken. "Diverging Clear", "Slow Clear," "Medium Clear" are all "reduced speed through (diverging route of) turnouts and interlocking" and clear to next signal. "Diverging/Slow/Medium Approach" are all "reduced speed through turnouts/interlocking at next signal. "Approach Diverging/Slow/Medium" will generally imply that the next signal is showing a reduced speed (because of a divering route lined) gregc can signals have different meanings depending on location? or would operator understand the implied meaning of a signal depending on location? No not really. The meaning of the signals is laid out unambiguously in the rule book. However the possible indications and the reason a specific indication is displayed on a signal depend on the possible routes and conditions at the location of the signal. But different railroads have different rule books and different sets of signal indications. You'll note that the NORAC and GCOR rule books you mentioned are completely different.
gregc it's not clear to me how signals indicate route.
Any indication that has "Diverging" or a speed indicated in it, implies a different route being taken.
"Diverging Clear", "Slow Clear," "Medium Clear" are all "reduced speed through (diverging route of) turnouts and interlocking" and clear to next signal.
"Diverging/Slow/Medium Approach" are all "reduced speed through turnouts/interlocking at next signal.
"Approach Diverging/Slow/Medium" will generally imply that the next signal is showing a reduced speed (because of a divering route lined)
gregc can signals have different meanings depending on location? or would operator understand the implied meaning of a signal depending on location?
No not really. The meaning of the signals is laid out unambiguously in the rule book. However the possible indications and the reason a specific indication is displayed on a signal depend on the possible routes and conditions at the location of the signal.
But different railroads have different rule books and different sets of signal indications. You'll note that the NORAC and GCOR rule books you mentioned are completely different.
Great explaination Chris, especially this part:
The meaning of the signals is laid out unambiguously in the rule book. However the possible indications and the reason a specific indication is displayed on a signal depend on the possible routes and conditions at the location of the signal.
wjstixI believe the term came about because in the days of mechanical linkages and levers being used to throw the switches and signals, the linkages were 'interlocked' in such a way that a towerman couldn't set the signals in a way that could cause an accident.
Here's one look at how the levers are connected (interlocked) with movable tappet bars and locking bars so that a proper route can be established and as you point out an erroneous signal cannot be displayed.
Interlocking Machine by Edmund, on Flickr
I think the New York Central "Signal" film has a segment explaining and showing the levers moving. You can find it on YouTube.
This should begin at the 'interlocking' segment:
Regards, Ed
gregc i was trying to ask if there's a difference between a two-headed signal and a two-headed interlocking signal?
Yes, but it isn't in the signal, it's in how the railroad uses signals.
In block signaling, one head displaying two (red or green) or three indications (red or yellow or green) usually is enough. Red means the next block is occupied, yellow means the next block is clear but the one after that is occupied, and green means the next two blocks are clear.
Interlocking signals are used at places where railroad lines diverge or cross. I believe the term came about because in the days of mechanical linkages and levers being used to throw the switches and signals, the linkages were 'interlocked' in such a way that a towerman couldn't set the signals in a way that could cause an accident. Like say where two railroads crossed each other at grade; setting the signals to clear for one line automatically changed signals for the other line to stop. There would be no physical way to change the one line to clear while the other one was at clear.
Interlocking signals virtually always use two or three heads. This is partly so that the signals are recognized as being 'absolute'...a red signal doesn't always mean 'stop' on a real railroad, but if there are multiple heads (2 or 3) all showing red, it always means stop. When two railroads cross each other, you want to be sure one trains stops to let the other go by!
Interlocking also tells the crew of a train how a switch or switches are set. Green-over-red means you're clear to continue on the track you're on. Red-over-green means you're diverging off that line - onto a branchline, onto the other line of a double-track main, or onto a passing siding.
In more recent decades, railroads have switched to signals based pretty much only on speed. They often use multi-head and blinking signals to convey speed settings. So although a two-head signal in that situation would physically look just like a two-head interlocking signal, the information each indication gives would be different.
gregcit's not clear to me how signals indicate route.
gregccan signals have different meanings depending on location? or would operator understand the implied meaning of a signal depending on location?
Chris van der Heide
My Algoma Central Railway Modeling Blog
Sheldon has explained this very well! I'd just add that a few railroads (New York Central) used two-head signals as block signals because with the combination they had of high speeds and relatively short blocks in some areas, a train getting a yellow (slow prepare to stop at next signal) might have less than a minute to slow down to be able to stop. I think (going by memory here) green-over-green was clear, then when a train passed it went red-red, then yellow-red, then yellow-yellow, then green-green.
On my layout, I get by with two-head/two-light interlockings for the most part. If you're on the main and come to a switch that could send you to a branch line, green-over-red means you're continuing on the main. Red-over-green means you're going on the branchline. I haven't set up detection yet, but red-over-red would mean the block ahead was occupied and you had to stop.
BTW a single red signal in real railroading can often be 'permissive', you really just have to slow way down or stop and then proceed. Two head signals can be used to ensure the crew of a train knows that it's an absolute stop, red-over-red. In some cases, like where a railroad crosses another railroad, one head might be a 'dummy' head that only can show red. So green-red, you're OK, red-red, you must stop.
You want to get way into the details, find a copy of "Railroad Operation and Railway Signaling" by Edmund J Phillips Jr, copyright 1942, reprinted 1953 by Simon-Boardman Books.
or,
"Guide to Signals & Interlockings" by Dave Abeles, 2021, Kalmbach Media
or
"Operation Handbook for Model Railroads" by Paul Mallery, 1979 by Tab Books, reprinted 1990 by Carstens.
"Model Railroad Electrinics" by James Kyle, 1977 by Tab Books.
Find Bruce Chubb's orginal relay based signal system articles in MR, sometime in the early 70's.
You will then spend hours and hours boiling down that information to what I have already explained three or four times now.
gregc ATLANTIC CENTRAL Stop looking at those charts and find a more complete book on signals. which one are you looking at?
ATLANTIC CENTRAL Stop looking at those charts and find a more complete book on signals.
which one are you looking at?
Do you mean what book? Try this one.
https://www.amazon.com/All-About-Signals-John-Armstrong/dp/0890245029
It was written 67 years ago.
I'm not looking at any of them, there is more to signaling than those charts. I learned all this four decades ago, I can get by without the chart.
In real life the railroad have reasons why they use the charts and teach the engineers from a perspective that is different from how the signals work on a mechanical level - mainly that not all engineers are mechanically minded people.
But if you can find some old relay diagrams of how the signals are wired, you will see that what I am telling you is correct:
Top head = mainline
2nd head = primary diverging route or routes
Bottom head = secondary diverging route or routes
All conditions must be met to get a clear indication - one of those conditions is turnout position.
Only one route can show clear at a time, so I guess that means the turnout is set to that route if the signal is anything but red.
Greg,
Signal systems have to be adapted to endless possible track arrangements.
BUT, at its most basic level, at an interlocking, the top head indicates the status of the mainline or highest speed route.
The second head indicates the status of the next highest speed/importance route, the third head indicates the lowest, most speed restricted route - even if the routes are not phyically in that order.
The branch to the yard may be the first route you physically come to, but it will be indicated by the bottom head.
So, a single turnout interlocking would have a two head signal as you approach the points. If the top head is green, the turnout is set for the main and the track ahead is clear. The bottom head WILL be red in this case, there is no other choice.
If the turnout is set for the diverging route, the top head WILL be red, and the bottom head will be red, green or yellow depending on the speed restriction and track status ahead.
So, if you approach that turnout and see R/R, you do not know which route is set, but you don't need to know that, you know that you have to stop. But when the signal changes, then you will know which route is selected. If the top head goes green or yellow, the mainline route is set, including the turnout.
If the bottom head goes green or yellow, the diverging route is set, including the turnout.
You can believe me or not, I don't have 100 pages of prototype "proof" at my fingertips to direct you to. And I don't have time to dig thru my library, search 70 years of MR for articles, etc, to give you references to look up.
ATLANTIC CENTRALStop looking at those charts and find a more complete book on signals.
gregc ATLANTIC CENTRAL indicate the route, or the correct speed for a group of possible routes it's not clear to me how signals indicate route. at least on one listing of signals (NORAC ed.7 Solomon) i see the following G/R/R (green over red over red) Clear R/G/R or R/G Medium Clear R/R/G Slow Clear this site, General Code of Operating Rules has R/G Diverging Clear R/Y Diverging Approach can signals have different meanings depending on location? or would operator understand the implied meaning of a signal depending on location? ATLANTIC CENTRAL So why not use them to indicate route selection on our model layouts? because we don't want the expense of multi-head signals
ATLANTIC CENTRAL indicate the route, or the correct speed for a group of possible routes
it's not clear to me how signals indicate route. at least on one listing of signals (NORAC ed.7 Solomon) i see the following
this site, General Code of Operating Rules has
can signals have different meanings depending on location? or would operator understand the implied meaning of a signal depending on location?
ATLANTIC CENTRAL So why not use them to indicate route selection on our model layouts?
because we don't want the expense of multi-head signals
Stop looking at those charts and find a more complete book on signals.
At an interlocking that is what "Medium Clear" means, you are set for one or more higher speed dirverging routes.
R/R/G or R/R/Y means you are set for a slower speed more restricted diverging route.
G/R or G/R/R means you are clear for the primary high speed route.
So, common sense says that if there are only three routes, and there are three heads, each route is indicated by the conditions described above unless there is a train ahead that makes the signal go more restrictive.
If the interlocking is set for the mainline, but there is a train ahead of you in the next block, you will see R/R/R until it clears the block, then it will go Y/R/R when the train ahead clears that block and then G/R/R when it clears the next block.
The lower signals will stay red because those routes are not selected.
General rule books are just a guideline for developing a rule book for a specific part of a specific railroad.
And I can't say enough, before the 1980's there was no effort to make this stuff uniform from one railroad to the next.
ATLANTIC CENTRALindicate the route, or the correct speed for a group of possible routes
ATLANTIC CENTRALSo why not use them to indicate route selection on our model layouts?
gregc ATLANTIC CENTRAL Greg, your second question shocks me in that with all the study you seem to be doing, you don't understand this concept regarding signals. sorry if i wasn't clear. i was trying to ask if there's a difference between a two-headed signal and a two-headed interlocking signal?
ATLANTIC CENTRAL Greg, your second question shocks me in that with all the study you seem to be doing, you don't understand this concept regarding signals.
sorry if i wasn't clear. i was trying to ask if there's a difference between a two-headed signal and a two-headed interlocking signal?
Well that depends.
A permissive automatic block signal will generally have a number plate, or the designation "I". Absolute signals, which include interlocking (control point) signals will have no number plate or will be identified "A".
The problem here is there are endless prototype variations on various roads at various times in history.
Other than that, simply knowing where you are on the railroad is an important indicator.
As I have explained many times, it is the opinion of some with considerable experiance that model layouts don't really need permissive automatic block signals - our distances don't really support their function in most cases.
So a good approach is to use mostly or solely absolute signals on model train layouts - so nearly all the siginals will be interlocking signals.
Pretty simple idea, you come to a turnout or group of turnouts, two routes, two heads. Three or more routes, three heads and possibly some additional markers, dwarf signals, etc.
And again, interlocking signals do all of the jobs:
So why not use them to indicate route selection on our model layouts? With or without detection and other signaling features.
I'm not a western road guy, so someone can correct me if I'm wrong, but I believe the SP used two head permissive block siginals to convey the status of the next four blocks in front of the train in some locations.
So G/G meant you had four open blocks ahead. G/Y meant you only had three open blocks, G/R only two open blocks, etc.
ATLANTIC CENTRALGreg, your second question shocks me in that with all the study you seem to be doing, you don't understand this concept regarding signals.
gregc wjstix to see the positioning of turnouts ... I found using two-head interlocking signals helped a lot what signal aspects do you use that help indicate turnout position? what makes a two headed signal an "interlocking" signal?
wjstix to see the positioning of turnouts ... I found using two-head interlocking signals helped a lot
what signal aspects do you use that help indicate turnout position?
what makes a two headed signal an "interlocking" signal?
I suspect he is doing EXACTLY what I described above.
Generally speaking signals with two or three heads are interlocking or "control point" signals.
There are other uses for signals with multiple heads, but that is more advanced prototype stuff.....
Greg, your second question shocks me in that with all the study you seem to be doing, you don't understand this concept regarding signals.
This is an over simplification, but in my view it is the best way to start understanding interlocking signals.
EXAMPLE - You are approaching an interlocking with three possible routes.
Those routes are:
You have a signal above or to your right with three heads.
The top head has three aspects - G/Y/R
The middle head has three aspects - G/Y/R
The lower head has two aspects - Y/R
In simple terms, the top shows the status of the straight thru route, the middle head shows the status of the crossover route, and the lower head shows the status of the branchline/yard route.
That status includes turnout position, occupancy ahead, and in CTC territory, permission from the dispatcher.
Assuming no trains in the next two blocks ahead, and no CTC, these aspects will indicate which route is selected.
G over R over R = all turnouts aligned to allow your train to proceed straight thru on the mainline, all clear.
R over G over R = all turnouts aligned to allow your train to take the crossover to the parallel track, and implies whatever speed restriction is in the rule book for that interlocking.
R over R over Y = all turnouts set for your train to take the diverging route into the branchline/yard at the necessary restricted speed.
Detection of trains on the trackage ahead will override these aspects and make them more restrictive, changing them to R or Y.
R over R over R = absolute stop.
So even without detection, a modeler can use them to indicate turnout position and give some appearance of prototype signals.
What did you think that signals with two or more heads did?
Some railroads also used multi head signals as advance approach indications to provide status farther ahead than the next two blocks - but this is/was not common.
In between control points you would typically have automatic permissive block signals to regulate speed of trains following each other. They are typically a single three aspect head.
Looking at those rule charts for the signal aspects will never explain how they are applied to actual trackage.
You mentioned route signaling before - what I just described is route signaling at a control point. Speed signaling is exactly the same, with the possiblity that those three heads control more than three possible routes. So the Engineer does not know for sure which diveging route he will be taking, the combined aspects of the heads convey the necessary speed restrictions to him.
Example - G/R/R could be straight thru on the main, or there could be a full speed rated diverging mainline route in the interlocking.
wjstixto see the positioning of turnouts ... I found using two-head interlocking signals helped a lot
I believe - unless reproducing prototype signalling is really important to you - that having signals that are as simple as possible to get the job done is a good idea. My situation was different from the OP's; although my layout covers a lot of space, it's basically an around-the-walls shelf layout and only sees one train at a time, so block signalling wasn't really necessary. However, to see the positioning of turnouts 10-15 feet away, I found using two-head interlocking signals helped a lot - especially since I want to be able to run the layout at night. I connected the mainline turnout motors to decoders so I could throw them with my radio handheld controller from anywhere in the basement.
The signals I used are from China via ebay - they're pretty cheap, and come pre-wired with resistors for the LEDs. I did use a few two-light dwarf signals too.
Never mind.
ATLANTIC CENTRALAre you thinking that because you only want to use one signal head?
that's all we have
ATLANTIC CENTRALI don't understand why anyone would bother with signals and then try to define their function as a stand alone function and not link them?
don't understand what "define their function as a stand alone function and not link them"?
689
gregc ATLANTIC CENTRAL Not by my understanding, rule 288 implies two heads except as a dwarf right. i now see that it's a single dwarf. but ADVANCE APPROACH, rule 282-a is a sigle lamp flashing yellow. Finally pulled out my book (Solomon). but i hope you understand i'm not trying to be prototypical, just want to convey useful information to a modeler operating on a model layout. if they intend to take a diverging route, they should see flashing yellow, not green or yellow 596
ATLANTIC CENTRAL Not by my understanding, rule 288 implies two heads except as a dwarf
right. i now see that it's a single dwarf. but ADVANCE APPROACH, rule 282-a is a sigle lamp flashing yellow. Finally pulled out my book (Solomon).
but i hope you understand i'm not trying to be prototypical, just want to convey useful information to a modeler operating on a model layout. if they intend to take a diverging route, they should see flashing yellow, not green or yellow
596
I understand, but in my view flashing is just extra complication. Are you thinking that because you only want to use one signal head?
I know your not trying to be prototypical, but if you look at the list of aspects I use, I simply use the most basic prototype aspects and ignore the complex prototype aspects.
And I ignore permissive signals, except for my intermediate signals which give the appearance of permissive block signals between control points but require no extra logic because in function they are approach signals for the control point siginals.
We had this conversation once before, I don't understand why anyone would bother with signals and then try to define their function as a stand alone function and not link them?
But the linking can be basic, not complex like the prototype.
Even simplified, I think of it as a whole system, not just what a single signal does.
ATLANTIC CENTRALNot by my understanding, rule 288 implies two heads except as a dwarf
Not by my understanding, rule 288 implies two heads except as a dwarf in a yard or other slow speed situation.
Here is the thing, just because you put two heads on a mast, does not mean you have to actually light all the colors.
I have signals that have three aspects one of them never lights up.
Also, railroads often only installed two color heads where the third color would never be used.
I use type D signal heads (two or three vertical lights), a diverging route that is always speed restricted would only have yellow and red. The main route head above it would have green, yellow and red.
If the turnout is set for the diverging route and the detection is clear on the diverging route the signal will display red over yellow. This confirms both pieces of information, the turnout is set for the diverging route, and that route is clear of traffic.
A train ahead on the diverging route would set the signal red over red.
The top head would stay red any time the turnout is aligned to the diverging route. The bottom head would stay red any time the turnout is aligned to the main route.
Only the head for the selected route would respond to occupancy conditions ahead.
To explain my comment above about asects that never light, at a typical high speed interlocking a crossover would be protected by two heads in the direction of travel thru the crossover.
I do not use approach aspects at control point signals based on a train in the second block ahead - that is too far away to be of use to the operators, they are going to see two more signals before they get to the second block ahead.
So those are three aspect signals because they would be on the prototype, but they only show red over red, green over red, or red over green.
Here is the trap that you and others fall into - trying to match up the aspects you use to those "rule numbers".
Your operators are not going to learn that stuff.
All they need to know is:
all aspects red = stop
top aspect green = main route clear
top aspect yellow - approach, train in 2nd block ahead
second aspect green or yellow = diverging route clear, yellow indicates train in second block ahead or restricted speed
Third aspect yellow, restricted speed diverging route.
All aspects not described in each situation are red.
It does not need to be more complex than that for our models.
To make my system look more realistic and provide more info to operators I have a signal half way thru each block - it looks like an automatic block signal, but it is actually an approach sginal for the next control point signal.
If the next control point signal is green, the intermediate (approach signal) is green. If the control point signal is red, the intermediate signal is yellow. The intermediate signals have three aspects but they never show red, just like the main route control point signals never show yellow, partly because of the DC control system, these aspects would convey no useful information to the operators.