Early Railway Train Signals and Communication
Fixed railroad signals first used on railroads in the United States were Ball signals, derived from tide signals. Semaphores were used according to the old block system after 1851. Each block was one to seven miles long. As the train entered each block, the towerman put down his semaphore and notified the next tower by telegraph that rang a bell. After the train left his block, the towerman returned his semaphore to the safe position.
A photograph of semaphore signals on a railroad high in the Canadian Rockies
Color-light signals were introduced in 1912. Red, yellow, and green were used to indicate, respectively: stop, proceed with caution, and clear. Three years later, the Pennsylvania introduced position-light signals, reproducing the positions of the semaphore with amber lights in rows of three. Later, the Baltimore & Ohio combined the position and color lights, using two green lights vertically for clear, two amber diagonally for caution, and two red horizontally for stop. Other lines came up with different arrangements.
In the early twentieth century, the Railophone was introduced to railroading. It was a practical device by means of which telephone or telegraph messages and control signals were transmitted to and received from a train in motion. The transmission was affected by induction from a wire near the train. The current rang a bell to attract the attention of the train crew. Messages could be sent from a moving train to a distant station and received from the station by the train. Furthermore, it was also possible to automatically set the brakes on a moving train from a distant station by this device, and keep the train at rest in a block until they were released. Railroads equipped with the Railophone allowed a dispatcher who discovered two trains approaching each other on a single track to avoid a catastrophe by stopping one or both trains until matters were straightened out; so those old railroad signals were important.
This page was last modified on Wednesday, January 20, 2016