The automatic train control problem

Circumstances which make train control a pressing problem at the present time are mentioned. Certain desiderata are briefly discussed; the automatic control should act as a check on the proper exercise of manual control, not as a substitute; should conform to established safe signaling practises; should be designed for the severe conditions of railway operation; should not conflict with existing signals or otherwise introduce new hazards; should so far as possible conform to existing clearance lines; should not impede traffic; may be desired to exercise signal as well as control functions; may ultimately be desired for interlocking plants as well as main line tracks. Methods of transmitting and indication of track conditions to the train are described, (1) by intermittent mechanical and electric contact; (2) by intermittent induction through the use of permanent or electromagnets; (3) by continuous induction from the rails. Two general types of controlling action on the train are described, with some of their variations; (1) unconditional stop effective at a stop signal, with overlapping signal control, and (2) conditional stop effective at a caution signal. Relations between the type of controlling action and traffic capacity are discussed.