Automatic Train Control

Another form is known as the inductor type, and so far as the track element is concerned, consists of specially wound coils in a non-magnetic casing secured to the ends of the ties. These coils are connected to the signal system in such a way that a complete electric circuit is formed when the signal is in a "proceed" posi tion. The engine apparatus or receiver consists of coils in a casing usually attached to the tender truck and adjusted to register with the track inductors but with a clearance of about two inches. When passing over an inductor with a closed circuit there is no effect, but if the circuit is open, the current flow through the engine apparatus is so reduced as to permit the opening of a special valve, directly resulting in an application of the brakes. Nearly all of the intermittent train stop devices now in service are of the inductor type.

The Continuous System.

In this type a flow of alternating current through the rails is provided, resulting in an electrical field being produced around each rail. Collecting coils on the engine are so designed as to be sensitive to this field, and when passing through or near it the action is somewhat similar to that of a transformer, the rails being the primary, resulting in a flow of current from the receiver coils to the locomotive apparatus. This is amplified by means similar to that used in radio, and suffi cient current is produced to operate a relay, which, in turn, con trols the circuits of the engine apparatus. A notable development, the code system provides for the use of interrupted currents of varying frequencies in the rails, which, when picked up by the receiver coils and passed through selective apparatus on the loco motive, permit a number of indications to be transmitted.

Continuous train stop and speed control systems include audible and visible cab signals, the latter usually taking the form of col oured lights or rows of small white lights simulating the position of the wayside signal. Cab signals provide a continuous indication

of the track ahead and afford protection at all times against a switch being opened or a car or train fouling the main track even after the automatic signal has been passed. They increase the safety of train operation during fogs and storms when the wayside signals cannot readily be observed and permit regular schedules with full knowledge of the signal indications. Some railroads have installed two cab signals, one for the engineman and fireman, and an acknowledger, these in lieu of automatic train control devices. A failure to observe a restrictive cab signal results in a whistle sounding until acknowledged.

Speed control devices are used to require definite speeds as a maximum under certain conditions. These generally are in the form of a centrifugal device, attached to one of the locomotive wheels, and are capable of application to most of the systems in use. By means of electrical contacts closed or open at certain speeds, the brake controlling apparatus may be operated.

Automatic train stop devices are not new, but the first perma nent installation in the United States was on the Boston Elevated in 1899. In 1906, an investigation of this subject was started by a special board appointed by Congress, which work was carried on later under the Interstate Commerce Commission. This Commis sion issued orders in 1922 and 1924, requiring 8o passenger divi sions on certain railroads to be installed. Some voluntary installa tions have been made with the result that over 10,25o miles of road and 9,120 locomotives have been equipped with automatic train control or continuous cab signal devices. (G. E. E.)