(under the class definition) Systems in which a space
interval is maintained between trains on the same track, usually by the subdivision of the way into definite sections termed "blocks", the movement of traffic being governed by cab or wayside signals or devices which control the brakes or motive power, or both.
(1) Note. Home signals indicate the presence or absence of trains within the block about to be entered. Distant signals (usually semaphores having notched blades) indicate the condition of adjacent or distant blocks other than the block about to be entered. The combined functions of the home and distant signals are sometimes performed by a three-position signal, indicating by its three positions, respectively, the presence of a train in the block ahead, the second block ahead, or that both blocks are clear.
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19, for systems closely related in function where the physical possession by an officer of the train of a staff ticket or other token is a prerequisite to entrance upon the block.
