signal apparatus - ADDENDUM

NW Mailing List nw-mailing-list at
Mon Feb 8 19:00:09 EST 2016


Please ignore my last post, mangled as it was, and bear with me--I'm 
confused. Prior to WAB/NKP, could the N&W have used route signaling in 
the guise of speed signaling, beyond simply that speed can imply the 
route as route signaling implies the max speed? Or a hybrid system?

How early does "prescribed speed" appear in the rule books? This sounds 
like a route signaling term. How early do diverging-specific indications 
appear, regardless of name? Further, "medium" in an aspect name sounds 
like speed signaling, but eventually (or always?) had nothing to do with 
speed in Medium Clear, Medium Approach and Approach Medium, instead 
indicating "prescribed speed." I believe the indication for Approach was 
preparing to stop at next signal, later medium speed language was added, 
still later deleted?

Enginemen have acknowledged some confusion over "medium," but only in 
rules class--they knew their territory well enough to handle trains 
safely, regardless of semantics. What was less information about speed 
amounted to more train-handling flexibility. Could semantics be the only 
difference here?

Thanks, Abram.

Grant Carpenter

On 1/30/2016 11:42 AM, NW Mailing List wrote:
> I have a nice 8x10 Union Switch & Signal Co. photograph of a full, "four arm" PL signal somewhere on one of the Pokie Division branches, but all my US&S photos are now out-on-loan for scanning. When I get them back, I will post the photograph. It shows three full PL arms showing "Stop" on each of the three arms, with a the marker light below them all. It is probably the best photo that exists of such an arrangement on the N&W.
> There is one more observation to be made about N&W signaling, so here goes.
> There are TWO forms of railroad signaling:  SPEED signaling, and ROUTE signaling
> (1)  SPEED Signaling tells the Engineman at what speed he may proceed through turnouts and crossovers (Medium Speed = 30 MPH, Slow Speed = 15 MPH, and in the post-1940 world, Limited Speed = 40/45 MPH.)
> (2)  ROUTE Signaling, on the other hand, conveys no information about permissible speed through switches and crossovers, and the signals only tell the Engineman, "You will be making a turnout move, and it's up to you, buddy, to figure out how fast you can go!"
> When the N&W had semaphores, they were set up for Speed Signaling.  And when the N&W converted to PL signals in the 1930s, the new PL's exactly replicated the aspects and indications of the old semaphores, so they contained speed information, too.
> Likewise, when the N&W changed from 3-arm PLs to 2-arm PLs sometime in the 1940s, speed information was still built into the aspects and indications.  E.g. Approach Medium, Medium Clear, Medium Approach, etc.
> BUT when the N&W swallowed the Wabash and Nickel Plate in the early 1960s, those roads had only the old Route Signaling which had no nuance of maximum permissible speeds built into the indications.  (Those were both fast railroads, and I have always wondered why they never upgraded to Speed Signaling.)
> So... at the time of the WAB/NKP take over, someone in Roanoke made the decision to downgrade the N&W's good Speed Signaling system to conform with the clunky old Route Signaling system used on the WAB/NKP. And thus the words "Medium" and "Slow" disappeared from the N&W's signal names and indications, and were replaced with the word "Diverging."  Note, however, that this required NO FIELD CHANGES to the aspects shown on N&W PL signals... it was only a change of name and of the wording of the indications (the meanings) in the Rule Book.
> This would appear to have been a mistake because, under the revised scheme, the signals actually gave the Engineman LESS INFORMATION about how he was to handle his train.  Instead of being told by the signals how fast he could operate, he now had to look in his Time Table Special Instructions to determine the allowable turnout speed at XYZ interlocking, or wherever.
> Was this a fatal mistake?  Certainly not, as the huge preponderance of the N&W's interlockings were simple one-switch or one-crossover interlockings, and the railroad was not handling heavy traffic volumes with numerous passenger trains running on close headways, where the saving of two or three minutes on a move really counted.  And since N&W Enginemen by and large were confined to operating over a single territory for their entire careers, the permissible speeds were rather easy to memorize.
> I have always wondered how far up the N&W's food-chain this decision-to-downgrade went. We will, of course, never know.  My guess would be that it came from Dunlap, who most likely had no hands-on knowledge of the ins-and-outs of signal systems.  He had been a Yardmaster at Pulaski, if you will recall.  (Being related by marriage to Race Horse Smith didn't hurt his career advancement, either...)
> -- abram burnett
> advocate-at-large for the passe and the defunct
> ===========================
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