Following the original manual semaphore and the controlled manual system of operation came the pneumatic and electric systems, for localities which required a great number of signal movements. With the development of motors and batteries capable of economic operation, automatic signals of the semaphore type have been successfully and widely installed.
In the semaphore system numerous failures have occurred, due to the formation of ice and sleet upon the blades. This has led to the introduction of the so-called "upper quadrant" operation; that is, the motion of the signal being from horizontal to an upwardly inclined position and back.
On account of the widespread prevalence of electric lighting and the building up of the territory adjacent to railroads, changes in the color indication of night signals have been adopted, generally in such localities using green instead of white for the safety indication.
INTERLOCKING.
Developing with the manual operation of signals, and as a safeguard against mistakes of the signalmen, interlocking grew up as a means for preventing conflicting signals being given at the same time. As with signals, so with interlocking, England led at first. After a trip to that country in 1869, Mr. Ashbel Welch recommended the advantage derived from the English method of operating switches and signals in large yards and terminals, where the entire control fell to one man so located as to be in touch with the whole situation and equipped with a machine that would not permit of setting up conflicting routes. The plea resulted in the order of a twenty-lever Saxby & Farmer interlocking machine, which was installed in 1874 on the New Jersey Division of his line. Railroads were prompt to see its advantage, and in a short time machines performing the functions were made and installed in this country, not only for the protection of railroad intersections, but for the control of large terminal layouts. In 1876 the first power-operated interlocking system was perfected, which was the pneumatic type. In 1900 an all-electric interlocking system, advantageous where distant functions were to be embraced within the operation of the plant, and applicable to localities where electric traction was in use, was devised.
The more recent development of power-operated interlocking systems, with complete electric indication of the conditions on all tracks, has made it possible for larger systems to be consolidated under the control of a central plant, and thus under the direction of a central authority; these machines, being of a completely interlocked character, insure greater safety by the central control, as well as greater facility of operation.
TRAIN DISPATCHING.
In this country the first radical departure from the time interval and flagging method of operation came in 1851. The New York & Erie Railroad had established a single line of telegraph between Piermont, on the Hudson River, and Dunkirk, on Lake Erie, for company business. The Superintendent of Telegraph, Mr. Luther C. Tillottson, and the Division Superintendent were together in the Elmira depot on an occasion and learned that the westbound express from New York was four hours late. At Corning an eastbound stock train and a westbound freight at Elmira waited for the express. With this information, Mr. Tillottson suggested that the freight train at Elmira could be sent to Corning and the stock train at that point ordered to Elmira, with perfect safety, before the arrival of the express. The move was successful and encouraged similar operation, which shortly led to the adoption, with some modifications, of this train-dispatching method on the Susquehanna Division of the Erie. Its adoption over the entire line followed, in spite of the great opposition which Mr. Charles Minot, the General Superintendent, met when planning for its introduction. Some of the conductors and enginemen went so far as to resign rather than run on telegraphic orders against the time of another train.
This system spread rapidly to other lines and, in company with other features of railroad operation, has been progressively developed and improved. One of the important elements of safety in the dispatching practice has been the tendency to the same words in the same sequence to convey the same instructions, insuring a uniform understanding of the instructions instead of permitting a discretionary phraseology in originating or a misunderstanding in construing the order transmitted. The rules for train dispatching now prescribe the use of standard forms of expression for orders governing the movement of trains.