Signalling Practices for Interlocking (SP Donner Pass)

[jagged ben]

This is for the layout at our N scale club, but it's really a question about prototype signalling practices so that's why I'm putting in here.   

The club has an interlocking that follows the schematic in the attached pictures.   I'm curious if I have the correct concept on the signaling and also if the signalling can be simplified.   

We're not too nailed down on the traffic control method.   Assume for starters that it's CTC.  But I'd like to discuss if it would be different under APB with track warrant control.

The era here is basically 80's and 90's.  Think modern but with the signals still being searchlights.   Prototype is Donner Pass but our track plan does not follow the prototype, signals don't have to either.  But they should follow SP practices for the era, or at least present day UP.

Questions:

Is this correct?
https://drive.google.com/open?id=0BwBRBKEI1xrxeW9QTWM1OW5LeG8

Could it be done this way?
https://drive.google.com/open?id=0BwBRBKEI1xrxRkl0czdWTGdmVHM

(Okay I guess I need to look up the tutorials on image posting.   Will fix so you can see pictures in the post, if I can.)
(EDIT:  So I guess this doesn't work with Drive because the URL doesn't end in a file extension?  Or because they don't allow remote linking?  Lame.  I was hoping maybe I could avoid opening yet another website account.  Anyway, you should be able to view on the drive website, let me know if you can't.)   

[railnerd]

Could it be done this way?
https://drive.google.com/open?id=0BwBRBKEI1xrxRkl0czdWTGdmVHM

The inner signals are not needed, especially if this is a single interlocking on the prototype.

-Dave

[jagged ben]

The inner signals are not needed, especially if this is a single interlocking on the prototype.

-Dave

That's nice to know.

So is the red-over-yellow-over-yellow the correct aspect for a diverging route followed by another diverging route, even if there's no signal at the second one?  Or should it simply be red-over-red-over-green? 

[nkalanaga]

Based on Northwest practices (not necessarily the same as SP) I would say R-R-G, Diverging Clear.  Red over Yellow is Diverging Approach, used where the next signal is Red (Stop).  From your description, there is no "next signal", so Approach wouldn't be needed.

I couldn't find any aspect that had red over two non-reds, although that doesn't mean it doesn't exist.  On the other hand, it would be possible to define a signal aspect in the Special Instructions, as long as it didn't conflict with an existing aspect. 

In this case, if you need a special aspect for a double-diverging route, how about this:

G-R-R:  Clear, proceed on normal route (standard aspect)
R-G-G:  Proceed on diverging route, then on following normal route (not in my rule book)
R-R-G:  Proceed on diverging route, followed by second diverging route (Diverging Clear in the rulebook, but used for a single-diverging route)

R-G-R is also listed as Diverging Clear, the same as R-R-G, so it could be used in place of R-G-G for the second aspect above, with a note in the Special Instructions that it means to take the first diverging route, followed by the normal on the second turnout.  But in a case like this it might be valuable to have a special indication to alert the crew to the fact that there are actually three possible routes, not just Normal and Diverging.

[cv_acr]

In this case, if you need a special aspect for a double-diverging route, how about this:

Why?

Granted I'm not up on SP's specific rules, but anything I've ever seen it doesn't matter how many switches you're diverging through (whether one or ten), just that you're diverging. An interlocking with this schematic or similar would be pretty common.

If your railroad uses speed signaling like we do up in here in Canada (I believe most western US roads just used simple diverging route indications), the indication is based on the most restrictive speed rating in the particular route. (i.e. any number of "Medium" speed turnouts and at least one "Slow" speed turnout -> "Slow Clear" signal indication)

Really all you need here is the five* indications:

Clear
Approach *
Diverging Clear
Diverging Approach *
Stop

* Three if this is a purely isolated interlocking with no other signals further down. Anything with the word "Approach" in it indicates information about the state of the next signal down the line. as mentioned above.

Edit: oh, and almost forgot: if any route lined exits the interlocking onto an unsignalled non-main track, you'd get a Restricting indication.

[C855B]

... if any route lined exits the interlocking onto an unsignalled non-main track, you'd get a Restricting indication.

Bingo. Very likely any route into the "station track" would display a restricting aspect such as red-red-lunar. This was a common SP practice; I happen to have an SA head taken out of service in that general area (Roseville service region) with yellow, red and lunar roundels.

I think the only possible red-red-green indication would be if the station track had full signal detection AND the w/b exit was signaled AND its indication at the time was top yellow or green. IOW, red-red-green really would only be for a second diverging route with expected continuous travel into a signaled and clear block.

[railnerd]

That's nice to know.

So is the red-over-yellow-over-yellow the correct aspect for a diverging route followed by another diverging route, even if there's no signal at the second one?  Or should it simply be red-over-red-over-green?

When in doubt, find a rule book for your railroad.   Here is a handy set of SP aspects:

http://lundsten.dk/us_signaling/aspects_sp1996/index.html

[jagged ben]

Guys thanks for all the responses.  I'm going to respond to them backwards because it makes more sense somehow.  My first response to railnerd is really the question I'm asking,  which you guys have helped to clarify.

When in doubt, find a rule book for your railroad.   Here is a handy set of SP aspects:
http://lundsten.dk/us_signaling/aspects_sp1996/index.html

Yup, I've been aware of that page for a long time, even have it downloaded to my harddrive.   But it doesn't answer this question for me:

Is red-red-green equally appropriate for (a) and (b)?

a) First diverging turnout is closed, and then a bit down the same track a second diverging route is thrown.
vs.
b) Diverging route is thrown, bringing you onto a different track, where a second diverging route is also thrown.  (This is the situation in our trackplan.)

 

I think the only possible red-red-green indication would be if the station track had full signal detection AND the w/b exit was signaled AND its indication at the time was top yellow or green. IOW, red-red-green really would only be for a second diverging route with expected continuous travel into a signaled and clear block.

Well, yes.  Although it's not the question I was asking.    Red-red-green, red-red-yellow, red-red-lunar, the question is still whether the aspect of the three light signal is appropriate for the track arrangement.  It's really an 'is this correct route signalling' question.

FWIW, the station track is really also a yard lead, but it will be fully detected.   We might make it limited speed so that the aspect is never less restrictive than 'approach' even when the other end is lined  to go back on to a clear main track.     There are several turnouts on the station track, so probably it will be something like:
-yellow if not occupied and lined straight through to the end of the yard (next signal).
-flashing red if not occupied but any turnout is thrown within the yard limits
-red if occupied

Why?

Granted I'm not up on SP's specific rules, but anything I've ever seen it doesn't matter how many switches you're diverging through (whether one or ten), just that you're diverging. An interlocking with this schematic or similar would be pretty common.

If your railroad uses speed signaling like we do up in here in Canada (I believe most western US roads just used simple diverging route indications), the indication is based on the most restrictive speed rating in the particular route. (i.e. any number of "Medium" speed turnouts and at least one "Slow" speed turnout -> "Slow Clear" signal indication)

Okay, well SP didn't use speed signalling, it used route signalling, as far as I understand.  See the link railnerd posted, there's no "Slow" or "Medium" aspects, it's all pretty much just 'diverging' or not and a whole lot of 'next signal.' 

My question is actually pretty specific about the application of a three-light signal to arrangements with multiple diverging routes.   Your first comment speaks to that, but what's the deal with three-light-signals if the lower signal doesn't mean 'Slow'? 

Based on Northwest practices (not necessarily the same as SP) I would say R-R-G, Diverging Clear.  Red over Yellow is Diverging Approach, used where the next signal is Red (Stop).  From your description, there is no "next signal", so Approach wouldn't be needed.

Well there's a next signal within the interlocking in the first option I posted a link for, and not in the second.  So that makes a difference.

I couldn't find any aspect that had red over two non-reds, although that doesn't mean it doesn't exist.  ...

See Diverging Approach Diverging in the SP rulebook railnerd posted.   I didn't pull that out of my .   

To me there's no question that red-yellow-yellow would be the correct Southern Pacific aspect if you have that additional signal within the interlocking at the yard entrance.  The question is whether you can eliminate that additional signal, and furthermore how the applicable rules change because the 'next signal' is then somewhere else.

[nkalanaga]

Chris:  Thank you.  The only interlocking I'm intimately familiar with is (was) the Pasco NP/SP&S junction, and it had signals for nearly every turnout, besides not being that complicated.  I just assumed the usual way of doing it was to have a signal for each possible route.  Your experience trumps my untrained observations!

Jagged Ben:  A very good reason for finding a rulebook for the railroad one models.  "Diverging Approach Diverging" isn't in the 1959 or 1867 "Consolidated Code of Operating Rules" used by most Northwest and upper Midwest railroads.

It does, however, in the NP/SP&S-specific section, have one named "Flashing slow-clear, approach medium", which is red, or red-red, over flashing yellow.  Not to be confused with "Flashing medium-clear, approach medium", which is red-flashing yellow-red.  I never saw either of those in Pasco either.  All of the signals there had solid lights.

[cv_acr]

Well there's a next signal within the interlocking in the first option I posted a link for, and not in the second.  So that makes a difference.

Yeah, but that wouldn't really happen. Not signals inside an interlocking.

In cramped conditions you could have two interlockings right next to each other, so the next signal could be at the *exit* of the interlocking, but not inside.

The second track diagram has the location of signals for this interlocking correct. Not having looked at the SP signal chart yet, I'm not 100% sure on the heads. Check the rule book for how to display each indication: Stop, Clear, Diverging Clear, Restricting (and possibly Diverging Approach if there really are more signals down the line)

Chris:  Thank you.  The only interlocking I'm intimately familiar with is (was) the Pasco NP/SP&S junction, and it had signals for nearly every turnout, besides not being that complicated.  I just assumed the usual way of doing it was to have a signal for each possible route.  Your experience trumps my untrained observations!

Well, yes - every possible *entrance* into the interlocking would have a control signal. Depending on the complexity this may or may not have any direct relation to the number of switches, but every *track* will be protected.

A signal indication should be available for any possible route through the interlocking from each entrance, but in this simple route signalling example, with no other signals (apparently) on the line other than this isolated interlocking, any route basically has two options: Clear (straight route), or Diverging Clear (one or more diverging switches). (With a possible special case into the station track as Restricting.)

A "Diverging Approach Diverging" (or similar) indication would be seen only if you were diverging (through one or more switches/crossovers) at this interlocking, and also the *next* one down the line, if it's close enough to not have any intermediate block signals in between, as any indication other than Stop [and proceed] (i.e. Clear, Approach, Approach Diverging) would allow this signal to have a Clear indication.

In this example, the routes and indications would be:

From Main 1
...to Main 1 - Clear [+ Approach, Approach Diverging, etc. as req'd if more signals further down. If these are the only signals on the layout, just Clear will do]
...to Main 2 - Diverging Clear [+ Diverging Approach, Diverging Approach Diverging?]

From Main 2
...to Main 1 - Diverging Clear
...to Main 2 - Clear

From Station
...to Main 1 - Diverging Clear
...to Main 2 - Diverging Clear


(Right Side)

From Main 1
...to Main 1 - Clear
...to Main 2 - Diverging Clear
...to Station - Restricting

From Main 2
...to Main 1 - Diverging Clear
...to Main 2 - Clear
...to Station - Restricting

[cv_acr]

When in doubt, find a rule book for your railroad.   Here is a handy set of SP aspects:

http://lundsten.dk/us_signaling/aspects_sp1996/index.html

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.

[C855B]

... you can probably do everything with two-head signals.

Yeah, but that's no fun. There's so much joy to be had in stuffing wiring for three heads down microscopic brass tubing.

[cv_acr]

Yeah, but that's no fun. There's so much joy to be had in stuffing wiring for three heads down microscopic brass tubing.

Ha!

[John]

Yeah, but that's no fun. There's so much joy to be had in stuffing wiring for three heads down microscopic brass tubing.

thats why all my interlocking signals are 2 head, 3 lamps .. so much simpler, and takes less driver hardware also

[railnerd]

Guys thanks for all the responses.  I'm going to respond to them backwards because it makes more sense somehow.  My first response to railnerd is really the question I'm asking,  which you guys have helped to clarify.

Yup, I've been aware of that page for a long time, even have it downloaded to my harddrive.   But it doesn't answer this question for me:

Is red-red-green equally appropriate for (a) and (b)?

a) First diverging turnout is closed, and then a bit down the same track a second diverging route is thrown.
vs.
b) Diverging route is thrown, bringing you onto a different track, where a second diverging route is also thrown.  (This is the situation in our trackplan.)

Only M1 east signal needs a 3-light head, M2 east signal can be a 2-head signal.  Here's my rationale:

Think about what the routes are in the interlocking…  you have "westbound" route on M1 which would be Clear:

G-R-R

You have westbound M1 to M2 which could be represented as:

R-G-R

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

R-Y-Y


Main2:

For Westbound M2:

G-R

For westbound M2 to M1:

R-G

For westbound M2 to Station, you could use:

R-Y  (Diverging Approach)


Finally, the eastbound M1 and M2 routes (WEST signal bridge) could be two head as well.

-Dave