jeffhergert H<SNIP> I don't agree that waysides aren't has important anymore. That new technology (PTC) still fails. SNIP
H<SNIP>
I don't agree that waysides aren't has important anymore. That new technology (PTC) still fails.
SNIP
Jeff,
Oh, sure, maybe my suggestion that signals were no longer important was too strong. I didn't mean it to be.
My thoughts were that back in the steam days and perhaps even the very early Diesel days, the only form of communication between the ground and the crew was through signals whether they be wayside block or CTC signals, train order semaphores or a guy on the ground with a flag or lantern. Other than that, in order to get further communication the train had to be stopped at a wayside call box.
After the crews all had radios that changed somewhat so that wayside signals aren't as important as they once were. But neither can they be done away with.
I have long wondered what would happen if the PTC crashes? I would like to think that movements could still proceed according to wayside block signals. Or, one can at least hope. :)
Regards,
Fred M. Cain
If PTC fails, you revert back to wayside and/or cab signals. Some may have their cab signals integrated with PTC. We don't, although they will work with PTC. We have waivers to run without cab signals if PTC is operational. Even with the waivers, the lead engine must have cab signals and have had a departure test performed, in case the PTC fails enroute in cab signal territory.
Even with radios, block signals still govern now just as much as they did years ago. All radio really replaced was telephone communications. Orders and instructions can be issued directly, but the signals still hold as much authority now as then.
A 2-position semaphore only says either "red" or "green?" Seems like there would always be a need for some type of "yellow." No?
Lithonia OperatorA 2-position semaphore only says either "red" or "green?" Seems like there would always be a need for some type of "yellow."
The only way to provide a 'yellow' indication would be to provide motorized indexing and locking for an intermediate 30-degree position and putting a yellow lens there; the normal ways to show caution on a two-aspect signal (like the pre-'65 New York City traffic lights that lit both red and green together) won't apply to spectacles with only one light source. I am told in multiple sources that no lower-quadrant 30-60 degree system used other than the horizontal and 60-degree aspects -- so no yellow at home signals.
There is doubtlessly more about this that semaphore guys will know. I was a TVM guy in the '70s and a Patenall CPL lover before that, so I have little objective interest other than what I've read.
OvermodThat's done with the blade color and approach/home position -- the yellow-blade approach is 'always' yellow or green (with two yellows in the continuous view) and the red-blade home signal following the yellow-blade semaphore will be red/red/green (with two reds).
Thanks, OM, for responding.
But I really don't understand what you're saying. Referring to what I've bolded above, if we're talking about a single (LQ) semaphore, how can it have two yellow indications, and what would be the point? and what does "in continuous view" mean? Similarly, how can a single red blade have two red indications, and what is the point?
Following is what at first glance I thought you you were going to say. Yellow blade can only designate a distant signal; it's green at 60, and yellow at 0; no red indication is available. Red blade means it's a home signal; it's yellow at 60, and red at 0; no green indication is available.
I thought that would be a workable arrangement; however, I clearly must have that wrong. But maybe getting a glimpse of how I think can help you undersand what I'm missing. ??
Now, if you are talking about pairs of semaphores at each location, then obviously other possibilities open up.
I very much appreciate your input.
My understanding of an approach signal was that it had two heads. Both blade down was a full clear, lower blade down and upper plade horizontal was an approach and botn blades horizontal was a stop & stay.
You could be right, Electroliner.
That brings to mind this question: what is the difference between a distant signal and an approach signal. And what is an absolute signal?
I'm going to dive back into my books on this subject. After gleaning some knowledge on this board, the books may make more sense to me upon a second reading. I find this subject surprisingly confusing, TBH.
But isn't this two upper-quadrant semaphore heads, one over the other? As I recall, Rudd designed the classic PRR position-light system to replicate such aspects, which is why 'approach' tilts the lower head like / rather than \.
Lithonia: here are a few additional points. If you did not read what I said about 'Continuous Light Spectacles' you might want to look them up by name (as it was in one reference to them that I learned the correspondence of the non-green positions in a CLS to the blade color.)
Keep in mind that at the time of the CLS, automatic block signaling was still in comparative infancy, and I think you would usually find the usual three-position 45-degree upper-quadrant semaphore with red/yellow/green or equivalent being used for block warning.
The distant and home convention is for controlling approach to a fixed known hazard -- a crossing at grade, a drawbridge, gantleted track, a hard sharp curve like the one in the DuPont 501 wreck perhaps -- and this has only one aspect at 'stopping' distance, which is only a warning, and one for the actual stop.
We understand as a given that both the 'distant' and 'home' signals run continuously; if either were observed to be dark it would be the most restrictive indication possible. Now, when the route is clear through an obstruction like a crossing at grade or a properly-locked drawspan, both 'distant/approach' and 'home' will be green. On a 2-position signal that only leaves one other color, which is duplicated on a CLS so that if the blade sags it still shows a proper lighted indication. That can't be 'red' for approach, so the duplicated lens in the CLS matches the only other indication an approach signal shows -- which is yellow meaning 'prepare to stop at next signal'. (Note again that this is not a 'block' signal, merely a heads-up to let what might be a poorly-braked train get stopped at the 'home' location.)
Likewise the 'home' signal is interlocked in binary fashion. It would make no sense at all to have a home signal that either reads 'green' (utterly safe to proceed) or red (something impairing safe transit). Consequently the duplicated CLS lens is also red... so that any sagging 'fails safe'.
With searchlight signals you could use the same head and mechanism for both ABS and home/distant; in fact you could use the 'blink' feature to overload some route-signaling or speed-signaling information onto approach/distant. But this is not something a two-position semaphore would be used for.
I an not surprised that the 'color' of distant and home lower-quadrant semaphore blades will be made to match the light 'code' -- a yellow blade denoting distant/approach aspect with no confusion with ABS, and red meaning 'home'.
Don't take my word for it; as I said I'm not a semaphore aficionado.
Lithonia Operator... what is an absolute signal?
One meaning if 'absolute' is a stop signal at which you STOP, not 'stop and proceed at restricted speed' or whatever. As I recall PRR very elegantly provided this on 'upper and lower' position-light aspects with only a single, ominous light in the middle (the lower head usually only rigged to show vertical or 45-degree aspects). To railfans that light was a warning that (most of the time) a train was either imminent on that track or standing within the following block.
Thanks for all of that, OM. And yes, I'll go back and read earlier posts more closely.
I think that SP and the signal company could have saved us all a lot of trouble by just going with 10-50-90. Seems like 10 degrees separation from the post would have been clear enough to recognize that "it means it." And there would be the green spectacle also.
Lithonia OperatorI think that SP and the signal company could have saved us all a lot of trouble by just going with 10-50-90. Seems like 10 degrees separation from the post would have been clear enough to recognize that "it means it." And there would be the green spectacle also.
I wonder if the alternative of a 0-30-60-90 head, with the last position not used but equipped with a red lens, would be viewed as an alternative. It would use existing LQ conventions but allow the extra color. The problem that there appears to be no domestic record of anything but 60-degree two-position for this increment makes me wonder what the 'why not' reasons might have objectively been, though...
(Note that it might make more consistent 'sense' to write the lower-quadrant angles "correctly" for clockwise notation as 90-135-170 (or 165) from vertical. I will NOT be a nerd and number backward around the quadrants as though this were math class from Hades...)
Overmodit might make more consistent 'sense' to write the lower-quadrant angles "correctly" for clockwise notation as 90-135-170 (or 165) from vertical.
I agree. Just think of it as a compass, but it's vertical, then the degrees just are. (It wouldn't even have to be thought of as in relation to anything.) The top of the mast is North. Now, this "compass" reads True, not Magnetic.
Once upon a time, railroads (UP for instance) were known to use single-blade lower-quad semaphore automatic block signals, each one showing red or green, and each one preceded by a single-blade lower-quad yellow-blade semaphore showing yellow or green, maybe 2000-3000 (?) feet from the red/green signal. In later years the single-yellow-blade semaphores mostly disappeared; instead, many of the red/green semaphores got a second blade, a yellow fishtail blade on the same mast. Then if the top blade shows green and the bottom blade shows horizontal/yellow, that means the same as a yellow light -- expect the next signal to be red.
Terminology: don't call a signal an "approach signal". A signal can show an "approach" indication -- a yellow light -- but the signal is a home signal or a distant signal or both. Some home signals are absolute signals, most aren't.
timzSome home signals are absolute signals, most aren't.
Can you elaborate on this. I thought ALL home signals were absolute. If it shows a STOP display, it was a stop and stay. No Ifs ands or Buts.
Traditionally, in the US anyway, block signals were called "home signals" or "distant signals". I'd say any signal that can display STOP is a home signal.
If it's an automatic signal (with a numberplate) showing red, and the train is allowed to pass it slowly, after stopping, it's not an absolute signal, but it's still a home signal.
Think most RR rulebooks included "home signal" in the section of definitions. Stop-and-proceed signals are included.
The 1960 SP rulebook has definitions for Home Signal and Distant Signal.
SPRulebook.pdf (sphts.org)
(I see the definitions also include Approach Signal. I still say don't describe a signal as an Approach Signal -- it might be showing Approach, but it's better described as a home signal or distant signal or absolute signal or interlocking signal or something.)
timz(I see the definitions also include Approach Signal. I still say don't describe a signal as an Approach Signal -- it might be showing Approach, but it's better described as a home signal or distant signal or absolute signal or interlocking signal or something.)
We use the term approach signal for the last distant to a home/interlocking signal. Signal 541 is the approach signal to CP-Whatever. Not really that confusing.
Our rulebooks don't really get into those nuances anymore. I think those were left in the history books. If the signal has a number plate and red it means this - if it doesn't have a number plate it means this.
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
One interesting piece of trivia that I can add here, there WERE a few absolute lower-quadrant semaphores used in CTC territory on the SP. There weren't many, or should I say they weren't used extensively, but there were a few in some of the earlier CTC installations.
Here is a shot of such an installation in Texas (scroll down to the second photo):
http://www.carrtracks.com/tx101.htm
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