Before we leave the Baltimore & Ohio in Southern Indiana, I’d like to post one more note regarding their splendid choice for a signal system—that of the color position light, often referred to informally as CPL. The color position light was developed by Frank Patenal, superintendent of signaling of the B&O, around 1918 (source). I recall seeing the very same type along the old Chicago & Alton, later the Gulf, Mobile and Ohio, in central Illinois—I now realize the road most likely had them due to it being controlled by the Baltimore & Ohio Railroad. These signals are favorites of rail enthusiasts the world over for their complex and rich appearance. The “position” of the CPL mimics that of semaphores that came before them. The “color” of the CPL adds another layer of information to reinforce the indication. Simplifying here, the most common indications are—clear (or proceed), approach (or proceed at restricted speed), and stop. The additional “marker lights” can alter the simple indication to modify speed or indicate a diverging route ahead, etc. In any event, most signal systems around the United States have been replaced with one type, the color light—with separate green, yellow, and red lights positioned one over the other. To make matters worse, the signal is typically covered by a large sun- and snow-shade, hiding any of its inherent charms. |