1920 - Electrification near Bluefield, WV

[NW Mailing List]

It appears that the "colorings" on the back side of the semaphore arms you refer to are the product of an imaginative postcard colorist.

Railroads used Black on the back side of semaphore arms, so they would not be mistaken for some meaningful element of a signal aspect.

Recommended practices of the ARA (American Railroad Association) Signal Section were to use RED for semaphore arms used as Home Signals, YELLOW for semaphore arms used on automatic block signals. Early on (say before about 1920,) a few railroads used GREEN semaphore arms on distant signals (i.e. signals distant to a Home Signal of an interlocking.) A few roads used WHITE semaphore arms, but you would have to consult their Rule Books for specifics.

As I recall, the N&W's two arm semaphore automatic block signals used Red on the top arm, and Yellow on the bottom arm. Those colors conformed to the logic: The top arm governed the entrance to an automatic block and was therefore Red, and the bottom arm indicated the condition (occupied or un-occupied) of the second block ahead, so was painted Yellow.

Simple system. Once the logic is understood, the meaning of any signal aspect is instantly transparent. And that is as it should be.

The shape of the end of the semaphore arm was also meaningful. As recommended by the ARA, a square end indicated a Block Signal. A fish-tail end indicated an automatic block signal. A scalloped end indicated a Train Order Signal. I do not recall the ARA recommended practice on diamond pointed ends, but some railroads used those for Train Order Signals.

-- abram burnett
In the Science of Turnipology, N = 1 
.
.