Change of N&^W Signal Aspects, ca. 1940s

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Sometime in the late 1930s or the 1940s the N&W changed its Position Light Signal Aspects. 


The earliest N&W PL aspects, dating from the 1920s, used the rows of lights simply to replicate the position of the earlier semaphore arms. There are extant photographs showing N&W signals in the 1940s having three circular backgrounds, and the pattern of lamp illumination clearly mimics the positions of the semaphore arms on a three arm semaphore signal. 


Sometime in the 1940s, a new scheme of aspects was adopted allowing all indications to be given using only two backgrounds, and involved the reversing of the angle of the lamps in the bottom arm for the Restricting aspect (then called "Caution",) to its present configuration, and elimination of the bottom arm (background) from the earlier PL signals. With this change, the N&W basically adopted the scheme developed between 1915 and 1922 by Alexander Holley Rudd, Chief Signal Engineer of the PRR and designer and father of the PL signal. 


My question is... Has any deliberative or descriptive material survived from the N&W records pertaining to this change? 


My reason for asking is that I'm building a scaled-down version of a 3-arm N&W PL signal using the earlier, original N&W PL aspects, and worked off two levers from a 1909 Federal Railway Signal Co. interlocking machine. I'll have to build an integrated circuit to get five signal aspects from two levers each having only two positions, but the electronics will be well hidden ! 


My next question will be about the introduction of coded track circuits on the N&W in the 1930s, but we'll hold that for now. 


Thanks for any information. 


-- abram burnett 
( кирилл, самий малий ) 
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