Model Railroading > SP Signals - Flashing Yellow

Understanding railroad signals is a bit of mystery to me.  Trying to equate them to traffic lights will only get me so far.  Railroad crews study them and must pass tests to confirm their understanding.  Each railroad seems to have their own interpretation of what the combination of colors and positions mean.  I am narrowing my focus to the SP operations over Tehachapi in the late 90's.  

Here's a PDF of the Signal Aspects of the Southern Pacific:

https://railroadsignals.us/rulebooks/sp98/SPaspects.pdf

From that set of Rules, I'm trying to decipher how this translates to signals on a model railroad.  Specifically, where the Flashing Yellow signal would be.  Is the attached diagram correct?  If I am in the Purple Train, and the Red Train is stopped ahead of me, are the color aspects in the correct order?

The reason this matters is I want the logic for my signals to match SP practices.  It is my understanding that the Flashing Yellow was introduced to allow for more time to slow a train, since a single block may not be enough distance for a long/heavy train.

BTW, this video does a nice job explaining those signals with 3 heads.

          youtube.com/watch?v=JPI_JG_4pYs&t=5s              (Cut-n-paste that into your browser, since TrainOrders doesn't allow live links to YouTube.)

It is pretty long, and will take a few viewings to unpack all of the information, but helps "decode" Railroad Signal Rules.

Thank you in advance for sharing your expertise.  :-D
Dave
 



Edited 2 time(s). Last edit at 06/05/23 04:10 by tmotor.

---

I believe you are correct, Flashing Yellow so the freight train reduces speed, then Yellow so they have time to stop at the next Red, or taking the diverging route at the siding.  For the portion of the SP that I'm modeling (Cal-P between Oakland and Sacramento), it was rebuilt to 2 Main Track CTC with higher speed crossovers to allow the Capital Corridor and San Joaquin trains operate at higher speeds around the freight traffic.  The Flashing Yellow was used in advance of a crossover to let the engineer know they would be taking the diverging route at the crossover.  So Flashing Yellow to slow down for the crossover speed, then Red over Green at the crossover so the passenger train could jump back up to speed once through the crossover.  It was fun to watch through the cab car windows when I used to commute on the Capital Corridor.

Nathan

On railroads that had double or triple head signals, the equivalent of a flashing yellow on the SP would be yellow-over-yellow (on a two-head signal) or yellow-over-yellow-over-red (on a three-head signal). The name of this aspect was called "adance approach."

Arrt House

San Joaquin Valley had double heads at intermediates in place of a flashing. Part of the CTC program of the early 60s. Andover westbound on Donner Pass was a double head for the crossover at Shed 47

Greetings Nathan!

> I believe you are correct, Flashing Yellow so the
> freight train reduces speed, then Yellow so they
> have time to stop at the next Red, or taking the
> diverging route at the siding.  
Thank you for confirming I'm on the right track.  

> For the portion
> of the SP that I'm modeling (Cal-P between Oakland
> and Sacramento), it was rebuilt to 2 Main Track
> CTC with higher speed crossovers to allow the
> Capital Corridor and San Joaquin trains operate at
> higher speeds around the freight traffic.  The
> Flashing Yellow was used in advance of a crossover
> to let the engineer know they would be taking the
> diverging route at the crossover.  So Flashing
> Yellow to slow down for the crossover speed, then
> Red over Green at the crossover so the passenger
> train could jump back up to speed once through the
> crossover.  
Good to know.  

It was fun to watch through the cab
> car windows when I used to commute on the Capital
> Corridor.
Cool to get the engineer's perspective of the signals ahead.  Good times!

Take care and God bless!
Dave

Greetings Art!

> On railroads that had double or triple head
> signals, the equivalent of a flashing yellow on
> the SP would be yellow-over-yellow (on a two-head
> signal) or yellow-over-yellow-over-red (on a
> three-head signal). The name of this aspect was
> called "adance approach."
Impressive you can interpret those signals.
I suppose if my job (and life) depended on it, I could do it.  :-0

Take care and God bless!
Dave

Greetings WAF!

> San Joaquin Valley had double heads at
> intermediates in place of a flashing. Part of the
> CTC program of the early 60s. Andover westbound on
> Donner Pass was a double head for the crossover at
> Shed 47
I have no idea how the Signal Maintainers keep all of that stuff going.  Seems like each signal has its own personality.

Take care and God bless!
Dave

Some of the flashing yellow weren't available on Espee lines until 1988-90. Many older searchlights had extra relays added to set up those signal aspects. That's what signal maintainers told me when my favorite block signals suddenly began displaying flashing yellows. Prior to this, some signal circuits would display 2 "solid yellows" to protect a red signal.

It's far more helpful to go by the proper names of signal indications rather than the color aspects. Here are the most common signal names for single head signals.
Stop = Red
Approach = Yellow
Advanced Approach = Flashing Yellow
Clear = Green
Restricting  = Lunar or Flashing Red .... operate at restricted speed past signal

For double headed signals, here are some common indications
Stop = Red over Red
Approach = Yellow over Red
Advanced Approach = Flashing Yellow over Red
Clear = Green over Red
Diverging Approach = Red over Yellow (signal at switch)
Diverging Advanced Approach = Red over Flashing Yellow (signal at switch)
Diverging Clear = Red over Green (signal at switch)
Diverging Restricting = Red over Lunar or Flashing Red (often entrance signal into a yard)
Approach Diverging = Yellow over Yellow (signal one block before signal at switch with a Diverging Approach Indication)
Approach Restricting = Yellow over Lunar (signal one block before signal with restricting indication, often the Diverging Restricting into a yard.)

I hope by reading and understanding these basic signal indications, you will understand the basic core of the signal indications and how they work together. For model railroad purposes, I would drop the adanced approach indications as you will rarely have more than one intermediate signal between control points.

Ted Curphey
Ontario, OR

gonx Wrote:
-------------------------------------------------------
> Some of the flashing yellow weren't available on
> Espee lines until 1988-90. Many older searchlights
> had extra relays added to set up those signal
> aspects. That's what signal maintainers told me
> when my favorite block signals suddenly began
> displaying flashing yellows. Prior to this, some
> signal circuits would display 2 "solid yellows" to
> protect a red signal.
That might have come from the merger with the DRGW. They had flashing yellow

funnelfan Wrote:
-------------------------------------------------------
> It's far more helpful to go by the proper names of
> signal indications rather than the color aspects.
> Here are the most common signal names for single
> head signals.
> Stop = Red
> Approach = Yellow
> Advanced Approach = Flashing Yellow
> Clear = Green
> Restricting  = Lunar or Flashing Red .... operate
> at restricted speed past signal
>
> For double headed signals, here are some common
> indications
> Stop = Red over Red
> Approach = Yellow over Red
> Advanced Approach = Flashing Yellow over Red
> Clear = Green over Red
> Diverging Approach = Red over Yellow (signal at
> switch)
> Diverging Advanced Approach = Red over Flashing
> Yellow (signal at switch)
> Diverging Clear = Red over Green (signal at
> switch)
> Diverging Restricting = Red over Lunar or Flashing
> Red (often entrance signal into a yard)
> Approach Diverging = Yellow over Yellow (signal
> one block before signal at switch with a Diverging
> Approach Indication)
> Approach Restricting = Yellow over Lunar (signal
> one block before signal with restricting
> indication, often the Diverging Restricting into a
> yard.)
>
> I hope by reading and understanding these basic
> signal indications, you will understand the basic
> core of the signal indications and how they work
> together. For model railroad purposes, I would
> drop the adanced approach indications as you will
> rarely have more than one intermediate signal
> between control points.

Just a nitpick, there is no second "d" in Advance Approach (or other aspects with the word Advance in their names).