Nostalgia & History > “SA” or “Semi Automatic” letter signs - SP signals

What in hades is a Semi-Automatic interlocking in SP parlance?

(No inane gun jokes please).....

Posted from iPhone

The letters "SA" were applied to the masts of Interlocking signals that were partially controlled by a track circuit in automatic block signal teritory, and partially controlled by an interlocked device.  The interlocked device might be a spring switch, but was usually the last (or only) controlled interlocking signal at a tower, which also controlled the first  track of automatic block signal beyond the SA signal.

The idea of this was to provide a train a way to pass a red interlocking signal with instructions in a signal case at an automatic interlocking.

Say you are at the end of double track in ABS territory with a trailing-point spring switch  and a red SA signal.  You have train order authority to proceed, but can't because of the red SA.  The rules require you to line the spring switch and check it for obstructions, etc. which you do, but the signal stays red because the track circuit is down in the single main track beyond the switch.  The 'A' part of the 'SA' allows you to pass the red signal by the ABS rules.
G

You are leaving CTC into an Automatic Block System (ABS). Back in the day,  west end of Indo, California there was a SA control signal. You were leaving CTC into Double Track ABS.



Edited 1 time(s). Last edit at 03/24/20 10:59 by HardYellow.

Thank you both for the explanation. I had in mind the crossover in Tehachapi from the north track eastward to the south track. I suspect it was the north to the south for westbound traffic and it all ended at the WSS Cable, where (I presume) ABS ended and CTC began.

Bob

ATSF100WEST......Out

Posted from iPhone

ATSF100WEST Wrote:
-------------------------------------------------------
> Thank you both for the explanation. I had in mind
> the crossover in Tehachapi from the north track
> eastward to the south track. I suspect it was the
> north to the south for westbound traffic and it
> all ended at the WSS Cable, where (I presume) ABS
> ended and CTC began.
>
> Bob
>
> ATSF100WEST......Out
>

Correct...if the dispatcher brought you up the No.1 Tk (north) at the west switch Cable, you crossed back over at Tehachapi to the eastbound main (DT). So you were leaving CTC intering ABS Double Track. Going west, the CTC began at the Tehachapi Crossover. I would think by now, UP would have CTC (2MT) all the way from Tehachapi to Mojave. My last run over that RR was in the mid 1990's.  Here's a photo of a westbound entering CTC on the No.1 Track at the Tehachapi Crossover.
 



Edited 1 time(s). Last edit at 03/24/20 17:47 by HardYellow.

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Rule 303 from my SP Rulebook dated 10-31-76.  Got this when I hired out in 1979.

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Also...going east at Yuma, the signals that authorized you at Colorado to move east into Yuma were both SA's. I understand the two tracks at Yuma are now CTC. Someone refresh my memory...when UP took over, did they do away with the SA signals? I remember, if it was SP in anyway, they had no use for it. They even removed most of the 1000 ft and 500 ft fouling poing (FP) signs in the sidings. 



Edited 1 time(s). Last edit at 03/24/20 16:05 by HardYellow.

HardYellow Wrote:
-------------------------------------------------------
> You are leaving CTC into an Automatic Block System
> (ABS). Back in the day,  west end of Indo,
> California there was a SA control signal. You were
> leaving CTC into Double Track ABS.

Also leaving Interlocking limits where Interlock rules applied (6xx Rules). A couple examples that come to mind, 16th Street interlocking out of 34th Street onto the Cal-P. The Martinez Interlock on to the Mococo Line, and even the Martinez Bridge Interlock. (ed - just noticed the post from SP4360, explained in Rules) 

Also, they would be present in CTC territory if another line departed  CTC main into ABS territory. An example would be Springfield Jct, west of Eugene,  where the main line continuing to Klamath remained CTC, but the line to Medford (Siskiyou line) is ABS.  All westward signals at Springfield Jct. had an S-A plate even if trains lined for Klamath continued in CTC territory. 



Edited 1 time(s). Last edit at 03/24/20 20:09 by BCHellman.

HardYellow Wrote:
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> Someone refresh my memory...when
> UP took over, did they do away with the SA
> signals?

You can't pin this one on the Union Pacific. The SP did away with SA plates when it went to the General Code rule book, which had no SA or A-Plates in the rules. A-Plates came down at the same time and hence forth all absolute signals on the SP were designated by the absence of a number plate. I want to say the change over to the General Code from SP rule book happened in early 1986.

Union Pacific also had A-Plates like the SP (but never SA Plates), and I believe the UP's A-Plates lasted well after SP discarded the A-Plate. What you might be thinking is that UP discarded the P-Plate for protective devices. That happened a couple years after the UP took over the SP.

A bit of SA plate trivia. When the SA plate made its introduction on the SP, it was also accompanied by a number plate, the number plate being the signal number as you would find on automatic signals. I think the SP dropped the number plate on the SA sometime 1932ish. I would have to research further. 

 

HardYellow Wrote:
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>  I would think by now, UP
> would have CTC (2MT) all the way from Tehachapi to
> Mojave. My last run over that RR was in the mid
> 1990's.

It is now CTC-2MT from Tehachapi to Mojave...but there is still just one crossover at Cameron, despite the signals placed far enough west(north) to allow the installation of the other.

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In really simple terms,it was an absolute signal, in ABS territory...

" What you might be thinking is that UP discarded the P-Plate for protective devices. That happened a couple years after the UP took over the SP."


You're correct...it was the "P" plates, along with the 1000ft & 500ft  fouling point (FP) sings, in the sidings



Edited 2 time(s). Last edit at 03/25/20 10:08 by HardYellow.