"Perhaps no single invention in the history of the development of railway transportation has contributed more toward safety and despatch in that field than the track circuit. By this invention, simple in itself, the foundation was obtained for the development of practically every one of the intricate systems of railway block signaling in use today wherein the train is, under all conditions, continuously active in maintaining its own protection.

"In other words, the track circuit is today the only medium recognized as fundamentally safe by experts in railway signaling whereby a train or any part thereof may retain continuous and direct control of a block signal while occupying any portion of the track guarded by the signal."

[1]

From the Third Annual Report of The Block Signal and Train Control Board to the Interstate Commerce Commission. Dated Nov. 22, 1910.