Signals in the Steam Age
In the earliest days of the railroads, trains ran up and down single tracks and signaling was not a necessity. As rail traffic and speeds increased, however, train safety grew to be a major concern and signaling became essential to prevent collisions. Hand and arm signals were soon replaced by flags and lanterns, and in 1832 the first elevated wayside signaling was introduced. By the 1860s, mechanical signals were in general use, but no single system was agreed upon. Semaphore signals were widely adopted in Britain, but were not standardized until 1923, while ball signals were commonin the US. Color light signals came into use from the 1950s.
A chief safety mechanism in train signaling outside the ...