Round signal demise

[NW Mailing List]

 Howdy,

 I worked as a Signal Maintainer on the Georgia Southwestern RR, but the old signal targets on the N&W are different from most other railroads and something I am not familar with. I am currently building an N&W layout and want to make it as prototypically correct as possible. 

 Can someone tell me what year the N&W stopped using the large round signal targets and went to the current type? Also, did they use any other type before using the current target faces? Next, what do the single light targets mean or what is their use? I have seen these on bridge approaches on the New River. Last, what do they use the horozontal elongated double light targets for? 

 Thanks!

 Ken McWilliams