Hi,
Where and how might a dual head signal, such as this model by BLMA, be used?
Thanks,
Colin
based on where it is in the video, looks like it’s right before a switch onto a siding…
Several places based on the system used an location. It can be a distant signal indicating the next signal is a home signal. It could be a home signal into or out of an interlocking. Signal lights could be search light with all aspects from single lens or with three lenses per head. Aspect can be steady red on top with various aspects shown on bottom head only or it could be that both heads can show different aspects. Aspect ability would be determined by the system used and the rules in effect.
Usually it’s the signal governing a switch or crossover, or it is the automatic preceding the signal governing the switch or crossover.
In the US some RRs use speed signalling and some use route signalling; I’m guessing the majority of two-head US&S H2s like that one were on route-signalled roads like SP. On the SP a signal like that would be a CTC or interlocking signal with one power switch just beyond it, most likely to a siding. The lack of a number plate suggests it’s not any kind of automatic signal (not that automatic signals looked like that on SP anyway).
Now I read more of their description-- their signal is a model of a UP signal on their single-track CTC railroad between Las Vegas and Los Angeles. So the prototype has one switch to one siding beyond it. If the switch is normal, so an approaching train is going to stay on the main track, then the top H2 lights up green or yellow, and if the switch is set for the train to enter the siding the top H2 is red and the bottom is yellow (or possibly green?).
In the old days on SP when the top unit was green or yellow the bottom unit would be dark; dunno if UP did the same. Nowadays I think the bottom unit is always lit if the top one is.
Jamie tells me Basin siding isn’t track circuited-- I forgot to mention that possibility, that a train entering the siding would get red over lunar on the two-headed signal, rather than red over yellow. Then they’re supposed to enter the siding at restricted speed or some such thing.
There are several examples of two head signals, albeit not of searchlight signals, at Deshler, OH. The view is east from the diamond along the two-track main and across the single track that crosses it.
As I recall, the track west of the diamond includes both the NW and SW wyes and a crossover. That traffic would be governed by the two signals facing east just across the diamond. I don’t recall the westbound signals east of the diamond, so I’m not sure which signals would be governed by north-south traffic on the diamond for westbound traffic.
In the distance you can see three sets of two signals. Two sets are on the cantilever signal bridge - those control the main track (left set) and the SE wye (note the single lens in the top head). The third signal mast is just visible over the train about 10 cars or so back - that controls track 1. I believe there may be a crossover east of town as well.
Several legs of the wye and portions of the track south of the diamond are (or were) still controlled by B&O CPLs, which have their own set of modifiers regarding speed, etc.
The model has no number plate, so it’s an absolute signal. That means it’s right at the switch, not a block away.
Now notice the distance between the two heads. That was (no longer is) done to put the lowest head close to the ground, so you would think of a dwarf signal, and restricted speed. Wouldn’t be surprised if the top searchlight showed green, yellow, or red; the lower light would be (in UP’s case) red or lunar white.
Were this a CTC siding, with track circuits in it, those two heads would have been much closer together, and the bottom head would show green, yellow, or red. Or possibly yellow, red, and lunar white, particularly if the siding were one block long (a green on the bottom would suggest that the train was lined into the siding and out the other end, in this case).
In the old days, when head placement meant something, a distant signal would have had its two heads on opposite sides of the pole, as viewed from an approaching train, so the two signals wouldn’t be on a vertical line. Our distant signals on the east-west main line, when they were searchlights, were like this.
An SP two-head signal at the end of a circuited siding would be spaced just like the model. AFAIK the distance between the two heads doesn’t tell anything about whether the siding is circuited; can anyone find any mention of that in a rulebook?
By “distant signal” he probably means automatic signal.
You won’t find rules for any of this anymore. The rules will just show you the different possibilities, and say that they all mean the same thing, regardless of which side of the track, or which side of the pole (or how far apart) the heads happen to be.
By “distant signal” I meant distant signal–the signal in advance of an interlocking’s home signal. Call it an “approach signal” if you prefer.
I’m just going by experience and observation, and would appreciate any other plausible explanations someone can come up with.
I seem to be taken to task often for using old book of rules definitions and descriptions. Thus, dwarf signal is a specific low signal for back up or moves against the current of traffic at a switch or entrance to an interlocking and usually with only two aspects, red or yellow. A home signal is a signal at the entrence to an interlocking or at a switch which will indicate route and occupancy of a block to the next signal. Thus a distant signal would be the signal entering the block ahead of the home signal indicating that the next signal will be a home signal and possible give an indication of the route being displayed or the aspect being shown by the home signal…but an approach signal would be an aspect or indication of a signal and not the style or name of the physical signal. I believe the signal nearest to the track on the right is the signal governing that location unless otherwise provided by rule or bulliten or in single track territory. Each railroad had, and still has, its own system of signaling with style signals used, aspects used, name of aspect, and instruction of aspect. You can see two or three different railroads all using, say, a three or four light signal head but with each railroad having different combinations meaning the same thing or something entirely different from the others. Check through some old Trains or Railroad magazines or a pre NORAC book of rules some time, its fun and sometimes even confusing when you compare two railroads’ books!
You’re allowed to search in old rulebooks. Can anyone find a rule saying widely-spaced two-head signals mean something different from unwidely-spaced ones?
You’re saying signals with two heads, not vertically in line, are always followed by an interlocking signal. What about the rest of the two-head automatic signals along the line-- are they vertically in line?
Dwarf signals are dwarfs-- that’s about all you can say about them. They can have one head or two or even three; they can be interlocking or CTC or automatic, or maybe something else; they can show red, yellow, green, lunar, or maybe something else; they can be with the current or against.
Offhand guess: at least 98% of all the signals along US railroads used to be “home signals”. (Dunno if that term is still used.)
Timz. Did you read my opening sentence? Have you ever read a pre NORAC book of rules? If you haven’t done so, do so before you make anymore statements about signals or railroads and railroading… Your statements and comments indicate you haven’t and, although I hate to say it, you don’t really know what you are talking about but making conjectures without substance (and this isn’t the first time). Please, I hate to make comments like this, but if you did take the time to learn you wouldn’t be trying to make others look stupid or silly while actually making yourself look more so. I opened my explanation that I was using defnititions from pre NORAC books of rules. And they are specific as to what a dwarf, home, and distant signal were, and many other factors and definitions, etc… Today, yes, those definitions don’t necessarily hold true. But that does not negate what I said nor what the terms meant.
Could be a railroad existed that had definitions as you quoted. (Were you quoting from an actual book? Which one?)
Your definition of a dwarf is wrong for many? most? all? RRs. Ditto for your definition of home signal. For all I know your definition of distant signal may be almost right, on some RRs.
TIMZ! FIND AND READ THE BOOKS BEFORE YOU START RIPPING ME OR OTHERS APART. YOU ARE OFF BASE ON YOUR REMARKS BECAUSE OF NOT HAVING READ THE BOOKS. YOU DON’T KNOW WHAT YOU WE ARE TALKING ABOUT AND SHOW THAT YOU DON’T CARE TO KNOW. IF YOU DON’T CARE ABOUT FACTS, THEN AT LEAST STOP BEING SO INSIDIOUS. IF YOU DON’T BELIEVE WHAT I AM SAYING OR DON’T WANT TO ACCEPT IT, BASE IT ON FACT AND TRUTH AND NOT FROM YOUR IGNORANCE AND LAZINESS. GO TO THE SOURCES…THERE ARE THOUSANDS OF BOOKS OF RULES AND THE AAR CODE…EVEN ON LINE…THAT WILL EXPLAIN WHAT I’VE SAID AND OTHERS, TOO. I CANNOT CHANGE CHANGE THE FACTS AS THEY WERE. AND NIETHER CAN YOU.
Timz - you might find this site enlightening. They even discuss extra-wide spacing between the heads: http://www.railroadsignals.us/basics/basics5.htm#Staggering_Signals:_Stop_vs_Stop_&_Proceed._ _
There are several sections on signals on the site.
As has been mentioned - different railroads often assigned different meanings to the same aspect. That was the reason found for a rear-end collision in Chicago a few years ago - the engineer mis-interpreted a signal. He responded correctly to the displayed aspect, except that’s not what it meant on the track he was on…
Larry, thanks for posting that link–it’s perfect! And it does a good job of saying what I, in my less than stellar manner, was trying to.
Note that in the rulebook examples, all of the signals in each section mean the same thing. That holds true only on the railroad(s) governed by that book. Having had experience under two railroads in my working career, and several others in observational situations, I can attest to the differences that can come about from one railroad to the next.
When UP took over the C&NW, not much changed here, except that with upgraded lines we got to see some of the rules that we hadn’t seen before.
(If you look back to the Forum discussion on the wreck of the Pere Marquette on the south side of Chicago, you can see how far ahead of the public knowledge the Forum was when nailing down the cause of that wreck.)
Those dual head signals are used primary for fast main line service and are typically placed at a crossover between main lines. You need two signals because you will already be traveling at a certain speed on the mainline (say 40 mph), so you need the top signal to tell you what speed to continue going and a bottom signal to let you know that you are approaching a crossover.
On a normal train if you were not going to switch tracks the signal would likely read green over red. If you were crossing tracks the top signal would probably read yellow over red or flashing yellow over red. It all depends on what speed the crossover is rated for. The bottom signal will likely always be red regardless if you are switching tracks or not.
The other primary reason for a dual head signal is for a siding on the main line. In this case you will likely always see a dual head signal. This should not be confused with the hundreds of turnouts going to various industries and sidings along the main line. Sidings along the mainline re-connect to the main line.