I have a single line (A) crossed by another single line (B) at grade. Second line divides straight after the diamond to become 1st and 2nd Main (B1 and B2). All roads are bi directional, There is a running connection between A and B2. B1 is between A and B2. A and B1 (maybe B2) carry some passenger traffic.
I’m looking at Oregon Rail Supply’s 401 single searchlight and 402 double searchlight signals - which are the ready built versions of these two…
First question is whether these would be suitable for an interlocking or CTC controlling a diamond like this in the 80s?
2nd … I am assuming that I use one head where the route ahead doesn’t divide and a double head where it does. Is this correct? … or at least; one way of doing it?
Yes. Note that the picture of the 2-target signal shows the kit assembled with the heads staggered on opposite sides of the post, making that a block signal. A CTC control signal would have both heads vertical on the same side of the post. (The ORS signal is a kit, so will be able to be assembled in either configuration.)
That may depend on the signal rules of the road you’re modelling. On many roads an absolute stop is Red over Red, so even on a route that doesn’t divide or merge through the curved leg of the switch you’d have a 2-target signal, but the bottom light would never be anything but red. You see the same thing at the end of a controlled siding at the trailing end of the switch on the main track. The only possible route is straight through, but the bottom red is required for the absolute stop indication.
A signal head signal is typically a simple block signal, but on some roads depending on the signal rules in effect, could be used as an absolute control signal (especially with APB signalling, but also for CTC control signals depending on the signal rules in effect.)
Dave kindly provided me with a drawing…so here it is for everyone…
Assuming CTC, the protection for the diamond would be incorporated with the protection for the A/B and B/B crossovers.
Single head signals could govern the diamond’s North and East A approaches, most likely though, it would be a two headed signal with the bottom head permanently red. West and South two heads. East B could be a two or three head.
[banghead][banghead] AARGH! [:I] This always happens! [:(]
I really can’t get my head round US practice.
Thanks for the replies. [:)] They’ve completely thrown me. []
Area |(give or take 50 miles) is Chicago. RR… not sure… something like BRC or EJ&E. (Can’t say I’ve actually noticed any signals on either but I’m freelancing a bit). Time is 1980s. Line A has far-end-of-the-route Metra 1 an hour shuttle. Line B has one-a-day Amtrak. (This is all as waffled about in my previous “Chicago 80s” thread).
I’ve recalled… APB = Absolute Permisive Block. [:D] I think? [%-)] That’s scarey weird stuff. [xx(] I’d rather go for absolute signals probably with a tower but CTC would be okay.
It sounds like I might need to wait and get kits to put the heads where they need to be??? One two or three heads? Okay so an Absolute stop has two reds the lower one of which may be always red… can that one give a “proceed” of some kind if the route is set through the curve of a switch/ the lesser route?
Thanks for posting the scruffy sketch Nick [tup] Your answer has completley lost me though. [:I] Any chance you could sketch in the signals when you’ve got time?
Another thing that has come up is dwarf signals … I’m wondering if they would be combined to indicate routes set or instead of mast signals (maybe on the second main)?
Perhaps it will sort the location out a bit if I think in terms of one of the lines being a spun-off chunk of the bankrupt Rock Island? Or will that just rreally mess things up?
Would a recent change in the configuration of the diamond area make a difference… for example, lets say that the straight connection Line A (east) to Line B2
For slow speed through the diverging route, the green (or yellow) would be on the lower signal head. So a signal approaching the facing end of a siding switch would have 2 heads (for a Slow speed switch) and the indications would be Red/Red for stop; Green/Red or Yellow/Red for straight through, and Red/Green or Red/Yellow going into the siding. (Simplest case.) Coming out of the siding, or merging onto the main track through the curved part of the switch, if you are using a full mast signal on that track (which you would if it’s actually two main tracks going down to one) then the signal on that track would only ever have the green or yellow on the bottom (to display slow speed), and the top light would be permanently red.
Dwarf signals can be used instead of mast signals, but they’re used on secondary tracks, like a siding or other connection into signalled track. Dwarf signal indications are slower than the same combination of lights on a full mast (Green on a single-head dwarf is Slow-Clear, not Clear)
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Perhaps it will sort the location out a bit if I think in term
Note: With respect to 2-head vs. 3-head signals, it all has to do with speed.
The top light on a signal indicates “full” (track) speed. Eg. Green/Red is “Clear” (no special restrictions)
An indication using the bottom light indicates Slow speed. Eg. Red/Green or Red/Red/Green is “Slow to Clear” (slow speed through switches, then proceed at track speed.) (NB: under some rules a low yellow is actually “Restricting”, and a low flashing yellow is used for “Slow Approach” (aka. “Slow to Stop” under some rules))
An indication using the middle light indicates Medium speed. Eg. Red/Green/Red is “Medium to Clear” (medium speed through switches, then proceeed at track speed).
Some variations also allow for “Limited Speed” (not full track speed, but faster than Medium) but those are more complicated combinations of lights on a 3-head signal.
Also, if you’re taking approach signals to your interlocking into account, there are more possible indications on those approach signals as well, based on the speeds displayed at the next signal.
To wit, “Approach” (a.k.a. “Clear to Stop” under the current Cdn. rulebook) is your standard Yellow or Yellow/Red. (the next signal will be displaying Stop)
“Approach Medium” is Yellow/Green (the next signal will be displaying a Medium speed indication)
“Approach Slow” is Yellow/Yellow (the next signal will be displaying a Slow speed indication).
Nooooooo! [:O] Not approach signals Pleeeeease! [banghead] My head will explode!
[:D] Seriously, thanks. [tup]
If I can work through the sketch… Left to right first (eastbound).
RR A (top line) approaches the diamond and, once it has crossed RR B splits to add the Second Main. Length constraints mean that this will be a short crossover with slow speed. As I understand it so far a two head signal will show Green over Red for 1st Main and Red over Green for 2nd Main. - I’m wondering whether, if it’s a very slow crossover, the signal will have three heads and give Red over Red over Green for 2nd main? Would a 1980s alternative be two heads with Red over Yellow (no Green available)?
RR B (lower line) seems to need two heads. This is the new connection and laid with longer switches so I’m figuring that both heads will show Red or Green as appropriate. Green over Red for RR B’s route and Red over Green for 2nd Main.
Going the other way…
RR B can only go to RR B so this seems to be Red/Green over Red only.
RR A 1st Main also only has one route so that seems to be Red/Green over Red Only
RR A 2nd Main gets complicated… It looks like The top head will always be Red. I’m not sure which route will come next - to RR B through the faster switches or to RR A through the slow switch? Then there’s certainly the dead end spur and possibly a very slow connection to the switching loop…?
As I understand the answers so far the connections from the spur and switching loop coming out would be dwarf signals… might the spur be controlled by a derail with co-acting switch indicator?
The meandre of thought about the Rock Island was basically wonde
It does depend on the rule book since in the rule books with which I am familiar with the number of heads doesn’t have anything to do with whether or not its an absolute signal or not.
What makes it an absolute signal in most rule books is the abscence of a number plate or an “A” plate. A single head signal with no number plate is just as much a “stop” signal as one with 4 heads.
If you want some really bizzare signal systems, you should check out those in the UK. They make no sense whatsoever.
Its just a matter of what you are used to.
That makes it real easy. That makes it fall into GCOR era. The General Code of Operating Rules can be found on the web so you can read the rules that apply.
Actually its not scary at all. All it means is that when a route is cleared in one direction, all the opposing signals drop to red. Its what 99.99% of US roads use. Whenever anybody talks about “ABS” they are actually talking about APB.
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It sounds like I might need to wait and get kits to put the heads where they need to be??? One two or three heads? Okay so an Absolute stop
I guess I should have clarified that better (I may have as a result inadvertantly said something inaccurate), although of course, due to the variations the clarification is more complicated.
As Dave H. rightly points out, a single headed signal with round metal plate with an “A” on it mounted below the signal head displays an [Absolute] Stop when Red. The lack of a numberplate is often quoted as well, especially when demonstrating examples of APB signalling on western roads. I’m not sure if this rule in included in Canadian Rulebooks; I’ve never seen in used in practices. While it is possible to display (Absolute) Stop using a 1-head signal, I’ve never seen this in practice at any CTC control point or interlocking, although there may be exceptions on other railroads.
I should also have clarified that a signal with 2 or more heads where the heads are mounted vertically all on the same side of the post is an (Absolute) Stop when all lights are Red. In practice, this is the arrange
Or is this what you are talking about? I omitted the switching lead since its irrelevant for the diamond discussion.
What is the line I have the question about?
The only signal I have a question about are the ones at X. The one on the blue line will will be two heads and the one on the red line will be one, but the colors depend on whether connection is a signaled, bonded track or not.
All of the signals can display an approach signal if all the mains are CTC. The two headed signals will display a color over red for normal routes and red over a color for the diverging routes.
Why is approach such a big deal? All it means is to slow down and prepare to stop at the next signal. The speed through the turnout /crossover will be specified in the timetable/special instructions based on the size of the switch.
For a two-headed signal where two tracks are crossing each other at grade but there are no other route options, as was noted one head will often be a “dummy” which can only show red. Usually that would be the lower head, with the top being red-and-green or red-yellow-green. The problem with single heads in that situation is that a single head block signal is often “permissive” meaning a train doesn’t have to stop at it, it just has to slow down enough that it can stop in time if there is something on the track ahead. At a place where two lines cross, you want to be sure everyone understands that it’s an “absolute” stop indication that you can’t cross until you get the green signal.
In the drawing in the previous post, the X near to the blue line would be at least two-over-two so it could indicate that it’s clear thru the crossing (green-over-red) or that the track is set to turn to the right and not go thru the crossing (red-over-green) or a stop (red-over-red).
You could get by with a single head at the other X, but it might be better to add a dummy lower head so that to make clear that trains have to stop there.
BTW re the signal by the question mark in “what is this?” note that before about 1990 signals had to be above and to the right of the track they controlled, it’s only been in recent years that signals could be on either side of the track.
Under the 1980’s GCOR here are ONLY two stop signals. Stop and Stop and Proceed. Under GCOR a single red signal on a signal mast with a number plate only displays Stop and Proceed (regardless of the number of heads). ALL other all solid red indications are just that, Stop. It is very clear. Everybody understands that.
And a Stop indication can be crossed without it going to green. There is a whole list of conditions that permit that in the rules (rules 9.12.1 through 9.12.4). Everybody understands that too.
If Dave the Train absolutely must put two or three heads on every signal just so people don’t get confused, go for the gusto, but they aren’t really needed. Now if the interlocking was a manual interlocking built in the 1920’s or 1930’s and then modernized it might have older signals that might have more heads. Modern thinking is that if a signal with three heads means the same as a signal with two heads as a signal with one head, why add all the complexity if the indication is EXACTLY the same.
Sorry for vanishing. Between this post and the previous one I got called in to work in a hurry. Didn’t even change until after I got there.
I’ve been on the go all night - unplanned - so I’d not had any rest yesterday… so I’m shattered. However you’ve all put a lot of time in so I’ll get back with this now and then zonk out.
This is closer to what I’m up to. The “What is this” line is about where the dead-end interchange spur would be that Dave H has left out. South of that I have marked the approximate location of a parallel switching road. This will have (or have had) various spurs and loops off it and various docks/platforms. It willrun right across the normal (south) viewing side of the layout and disappear eastward and westward. The only connection to the Main tracks I plan to model will be at the east
Without having my printout of GOCR to hand (or a clue where it’s got to) I would guess that the list is like ours and about 24 items long including things like failed signals, failed locking, failed trains etc. Basically all the times they’ve come up with when a signal cannot be cleared but you have to get a train or loco(s) past it. I used to be able to quote the list but I didn’t know many who could and there were plenty of people who argued that you couldn’t do ones that you could and vice versa. (I knew one signaller who resolved such an argument with a manager by knocking him out. When the manager arrived at the other end and came to everyone was convinced he’d slipped and banged his head… so they got him out of the way in an ambulance and got on with the job[(-D] Ah! Those wer happy days!)
No. Dave the Train wants to put in the signals needed.
The issue is just what signals might have survived from as far back as the 30s and what new ones would be in place. then there’s a question of affordable rationalisation and requied consistancy/uniformity… bearing in mind that I’m reckoning that an
One thing that I can see is that for earlier signalling the use of a second head could be useful to help distinguish between a signal for the Secon Main and that for the First main for traffic in the same direction. IIRC someone posted that the 1st main would give Green over red while the 2nd main would give red over green. Something like that would have avoided the norton Fitzwarren smash in the 1940s.
Also I note the required location of signalsto the right or above the line they applied to. I take it that this is normal practice but that there could be (and were) exceptions where sighting the signal required. Southern of BR got up to a lot of interesting tricks to avoid “Wrong side” signal siting but since I’ve escaped into other parts of the country I seem to have fallen over posts in “the wrong place” all over the place.
All this is muddled in my desig by the fact that somewhere in the 80s my track layout has been altered and the A line Main tracks have been altered from directional to bi directional.
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