Signalling Practices for Interlocking (SP Donner Pass)

[jagged ben]

Finally taking a look at this link, it looks like there's 2-head versions of all the indications except "Diverging Approach Diverging" (R/Y/Y), so unless you need that indication on a particular route(s), you can probably do everything with two-head signals.

Notwithstanding the joy, or not, of stuffing wiring for three heads down microscopic tubing...  (trust me, I've done it)...

I'm thinking that the crew of a train coming from the right side on Main 1 needs an indication of whether they are just crossing over to Main 2, or whether they are crossing over and then entering the station.

I don't think it follows to say that because the every rule has a two light version that the three light version isn't needed in certain situations.  Otherwise, why have the three light version?  Why have both R-G-R and R-R-G? 

...

You have 'westbound' M1 to Station, and it would be perfectly acceptable to use:

R-Y-Y
...

First of all, crap, 'west' is actually east and vice versa, I should have flipped the drawing around to follow schematic convention.  Now I'll be thoroughly confused if I stick to your east-west nomenclature.    

Secondly...
I'm really beginning to think it should just be R-R-G here if entering the station, and no second signal and the station track entrance.  Otherwise you are really not following the 'next' signal rule as alluded to at several points in this thread.

[nkalanaga]

R-R-G sounds good to me for the station.  Three routes available, a green for each route, from the top down, should be clear enough, and, with no "next signal", "Approach" really wouldn't be appropriate.

On the other hand, there IS a "next signal" on the first diagram, at the turnout entering the station track.  So R-R-Y would also work, depending on what that signal displayed.  Suppose the station track was occupied?

[cv_acr]

You have westbound M1 to Station, and it would be perfectly acceptable to use:

R-Y-Y

...


For westbound M2 to Station, you could use:

R-Y  (Diverging Approach)

Not really, no.

The indications for routes from *either* main track into the station should be identical.

It can only be Diverging Approach or Diverging Approach Diverging if the track is detected & signalled and there's another interlocking at the other end. If it's unsignalled, then any route into the station would get restricting.

And according to the signal chart in the link above, Restricting can be done with a Red/Lunar or Flashing Red/Red. 2 heads.

R-R-G sounds good to me for the station.  Three routes available, a green for each route, from the top down, should be clear enough,

That's not really how signal indications generally work though... (That I know of?)

It is possible to see a situation that *looks* like it works that way with speed signals if the routes have different speed switches, but that's a bit more by coincidence. (And also doesn't apply here - not speed signalling.)

But then again, as I said above, I'm more familiar with Canadian speed-signalling practices than whatever SP does. But all their myriad variations on Diverging indications seem to mean exactly the same thing.

On the other hand, there IS a "next signal" on the first diagram, at the turnout entering the station track.

But as discussed above, that "rogue signal" by itself in the middle of the interlocking isn't really valid. (At least not that I've ever seen.)

I'm thinking that the crew of a train coming from the right side on Main 1 needs an indication of whether they are just crossing over to Main 2, or whether they are crossing over and then entering the station.

If the station track is unsignalled, Restricting takes care of that appropriately.

I don't think it follows to say that because the every rule has a two light version that the three light version isn't needed in certain situations.  Otherwise, why have the three light version?  Why have both R-G-R and R-R-G? 

That actually doesn't make a lick of sense to me that they have that many different valid variations of "Diverging Clear" - but ANY combination that has a green below a red all means the same thing: there's only "Diverging Clear" and R/G/R, R/R/G, and R/G/Unlit are all the same.

And they do Restricting in several different ways with either flashing reds or lunar lights. In the top, middle or bottom spots. All with the same apparent meaning under the same rule. That amount of variation is odd.

It's probably historical from the combining of several different older rulebooks from merged roads.

Maybe the practice really was in certain areas to always use 3 heads, but looking at the rules, you can totally do the entire interlocking with just two unless you need Diverging Approach Diverging.

[railnerd]

It can only be Diverging Approach or Diverging Approach Diverging if the track is detected & signalled and there's another interlocking at the other end. If it's unsignalled, then any route into the station would get restricting.

And according to the signal chart in the link above, Restricting can be done with a Red/Lunar or Flashing Red/Red. 2 heads.

Yeah, much simpler.  I didn't think of the station track as "dark"... but it could be.

[jagged ben]

The indications for routes from *either* main track into the station should be identical.

My understanding is that with SP route signalling, you get a different indication for crossing over to the other main than you do for crossing the main and then entering the station.   Note all the mentions of 'proscribed speed through turnout' in the rules.  How do you know the proscribed speed if it might be different for the different turnouts?

It can only be Diverging Approach or Diverging Approach Diverging if the track is detected & signalled and there's another interlocking at the other end. If it's unsignalled, then any route into the station would get restricting.

Okay, let's nip this part of the discussion in the bud.  The station track will be detected and there is a signal at the other end of it.    For the purposes of this discussion I should have just called it Main 3.   See previous post about it also being a yard lead for further interest, but this is not my question.  Yes, the indication of the bottom head on the three-light signal, whether it be green, flashing yellow, yellow, or red flashing, is obviously determined by what's further down the track.

Again, the question is really this:  Would SP just show red-red-whatever for entering the station in this track arrangement?  Or would they have required red-yellow-yellow (or just red-yellow) and a second signal?   I'm fine if the answer is the former.  It's easier to install and so far no-one has indicated to me that it would be wrong.

But as discussed above, that "rogue signal" by itself in the middle of the interlocking isn't really valid. (At least not that I've ever seen.)

Not 'valid' or just not necessary?  There's a section of the UP (old SP) line through Emeryville in California that has signals every 500ft or so, to handle multiple crossovers, and a yard entrance and station entrance.   So it seems that in at least some complicated situations the prototypes install extra signals.

But then again, as I said above, I'm more familiar with Canadian speed-signalling practices than whatever SP does. But all their myriad variations on Diverging indications seem to mean exactly the same thing.
...
And they do Restricting in several different ways with either flashing reds or lunar lights. In the top, middle or bottom spots. All with the same apparent meaning under the same rule. That amount of variation is odd.   It's probably historical from the combining of several different older rulebooks from merged roads. 
...
That actually doesn't make a lick of sense to me that they have that many different valid variations of "Diverging Clear" - but ANY combination that has a green below a red all means the same thing: there's only "Diverging Clear" and R/G/R, R/R/G, and R/G/Unlit are all the same.

The different lights on older SP three light signal refer to different diverging routes.  I've seen enough prototype examples to be reasonably sure of that.  So they are all the same rule, but they don't mean the same destination for the crew looking at them.

The duplication of red-flashing and lunar is presumably, as you say, because of legacy installations throughout the system.  Not sure if between Rio Grande and SP one of them used lunar and the other red-flashing, but that would be an explanation in the case of a 1996 rule table.

Maybe the practice really was in certain areas to always use 3 heads, but looking at the rules, you can totally do the entire interlocking with just two unless you need Diverging Approach Diverging.

Well, this is sort of what I'm wondering.  Precisely which situations would SP use a three-light signal for, or not?   But if you are wondering the same thing that's not helpful to me.   

[cv_acr]

My understanding is that with SP route signalling, you get a different indication for crossing over to the other main than you do for crossing the main and then entering the station.   Note all the mentions of 'proscribed speed through turnout' in the rules.  How do you know the proscribed speed if it might be different for the different turnouts?

...

Well, this is sort of what I'm wondering.  Precisely which situations would SP use a three-light signal for, or not?   But if you are wondering the same thing that's not helpful to me.   

Well I did say I'm not specifically familiar with SP. 

What Indication (name/meaning/rule - example "Restricting") you get at any particular point is easy to logic out, under any system. Which of the dozen possible Aspects (specific colour combination) to choose (L/R/R, R/L/R, R/R/L, W/T/F, ...) based on the particular signal rules chart, I have no idea at this point since there's about 8 or 10 variations of three head aspects that apparently seem to be entirely equivalent. I have no idea how that would tell you what particular track.

(Here I thought Route Signalling was just supposed to be simple as opposed to full speed signalling - you're either diverging or not - but you're implying that the system is also tweaked to somehow tell *which* track but the rules (at least as displayed on that site - I don't have a real SP full rulebook to look at) don't actually tell you how to determine that??)

Okay, let's nip this part of the discussion in the bud.  The station track will be detected and there is a signal at the other end of it.    For the purposes of this discussion I should have just called it Main 3.   See previous post about it also being a yard lead for further interest, but this is not my question.  Yes, the indication of the bottom head on the three-light signal, whether it be green, flashing yellow, yellow, or red flashing, is obviously determined by what's further down the track.

Again, the question is really this:  Would SP just show red-red-whatever for entering the station in this track arrangement?  Or would they have required red-yellow-yellow (or just red-yellow) and a second signal?   I'm fine if the answer is the former.  It's easier to install and so far no-one has indicated to me that it would be wrong.

If it's fully detected, and there's another signal, and the next signal is in any way capable of displaying a "Diverging" indication, then yes, "Diverging [at this signal] Approach Diverging [at the next signal]" is possible/required here.

[draskouasshat]

The change from lunar to flashing red was due to wanting to get away from a white light as a signal indication. Yes lists still are used but the railroads are trying to get away from them.
As for turnout speed, that is found in the timetable for the year you're modeling.
I don't deal with anything sp on the signal side not have I ever looked at it but I would just go with a 2 aspect signal and be done with it. As for a train everything a train entering a station track,I highly doubt you will have a green into that at all due to turnout speed restrictions and the fact that your most likelyentering a controlled siding if said station isn't Neff to the main.

As for signaling and why certain areas have certain aspects and how many slowly depends on what signal engineering decided was safedepending on train speed, weight, braking disturbance, permanent speed restrictions, and grade. GCOR rules don't tell you crap about a signal systems. If you want to know about signalling, be prepared because you most likely won't understand it. It defies the rules of electricity and stumps electrical engineers daily.

[nkalanaga]

"GCOR rules don't tell you crap about a signal systems."

Very true.  My rulebooks say nothing about the systems, only diagrams of the signals, names of the aspects, and what they mean.  And, yes, there are multiple ways to display most of the aspects, with no explanation WHY one would be chosen over another.  All the rulebook signal section is for is to tell the crew "If you see this, do this".

[John]

I have this book .. great source for figuring this out ..


http://www.amazon.com/Railroad-Signaling-Brian-Solomon/dp/0760338817/ref=sr_1_2?ie=UTF8&qid=1446848783&sr=8-2&keywords=railroad+signals

[nkalanaga]

I was sure there was a book out there SOMEWHERE that would explain it all, but also thought it would be one of those long out of print 1920s books Google has digitized. 

[jagged ben]

I found it really funny that Amazon's suggestion for books 'Customers Also Bought' is a book called 'Train Wreck'.   

Guys, I'm going with red-red-whatever for entering the Station/Yard as discussed above. 

Here's a very similar situation that has the same signal arrangement:
http://redoveryellow.com/signals/misc/22345_red_red_lunar_mojave.jpg
(This is 2003 but I'm pretty sure it's the same signal from the SP days.) 

The second diverging route (yard) diverges from the first diverging route, so very much the same as my example.   What's odd about the track arrangement beyond this signal is there are actually two mainline crossovers, only one of which leads to the yard.   Not sure what the signal would show if a train were taking the second crossover, but then operationally that probably would never be done.  And interestingly the signal for trains entering from the BNSF is the same arrangement, even though entering the yard seems to involve two crossovers before the yard entrance.  So it just goes to show that SP was very flexible in their use of 3-light signals.

Here's another, simpler example, in Oregon:
http://redoveryellow.com/signals/cs/722B_South_CP_VP582_Oakridge_24826.jpg
Again, a three light signal with no second signal when the second diverging route diverges off the first diverging route in short order).

(I knew that once I had some time to peruse redoveryellow.com I'd find some evidence.     )

Interestingly, I found similar arrangements on the BNSF between Portland and Seattle.
This one's the mirror image of my diagram:
http://redoveryellow.com/signals/cs/843A_North_Vancouver_25455.jpg

This one does have the second signal at the second diverging route:
http://redoveryellow.com/signals/cs/859_North_Longview_Jct_South_25422.jpg
http://redoveryellow.com/signals/cs/860A_North_Longview_Jct_25420.jpg

I'm curious what these former BN 3-light signals would display for different situations, but I gather red-yellow-yellow would not be among the aspects.  Diverging Approach Diverging (red-yellow-yellow) does not appear in this BN aspect table.    (It does appear in the first BNSF timetable.  Maybe that's for BNSF crews working on UP/SP trackage rights.)

[draskouasshat]

Ahhhh a book written by a guy that's most likely been inside a signal bungalow. It's kind of like having a children's book author write an essay about neuroscience for a medical journal.

I've scanned through that book a few times. I wouldn't take much in there for a grain of salt. The real world signalling is extremely complex and without doing the job and understanding all of the variables, you won't get far past what signal should be at clear or stop.  I'm really not trying to be crude, just voicing my opinion on this subject.

I would go off of prototype photos and any documentation you can find out about the area youre modeling to get an idea of what type of signals to use.

[cv_acr]

This one does have the second signal at the second diverging route:
http://redoveryellow.com/signals/cs/859_North_Longview_Jct_South_25422.jpg
http://redoveryellow.com/signals/cs/860A_North_Longview_Jct_25420.jpg

That's two fully separate interlockings. Notice the back of the signal bridge facing the other way in between. The first interlocking covers the crossover only. Then there's another one further down.

[jagged ben]

That's two fully separate interlockings. Notice the back of the signal bridge facing the other way in between. The first interlocking covers the crossover only. Then there's another one further down.

Ok but that's pretty much what my original question was: should this be treated as one interlocking or two?  I think the prototype examples prove it could really be either, depending perhaps on the distance between and the operations.

Also, note the three-light signals.  So regardless of how many interlockings you consider it to be I guess they still designate the route at the next signal.

[cv_acr]

Also, note the three-light signals.  So regardless of how many interlockings you consider it to be I guess they still designate the route at the next signal.

That's what I've said all along - the signal indication indicates what to do *here*, and also provides some expectation of what the *next signal* would be.

The only way you'd get a "Diverging Approach Diverging" is if this signal is diverging, and the next signal is diverging. Not simply diverging through two or more switches or crossovers in the same interlocking.

Exactly the difference between all the seemingly equivalent "Diverging Clear" indications is what is not entirely clear to me here.