Block.- In Automatic Block Territory, the length of track between two signals in the same direction, the use of which by trains or engines is governed by an automatic block or interlocking signal.

    In Manual Block Territory, the length of track between designated points or between open train order offices, the condition of which will be given as prescribed by the rules.

    Absolute Permissive Block (APB) System.- An automatic block signal system for a track signalled in both directions on which a train or engine causes STOP indication to be displayed on next opposing absolute block signal and STOP or STOP AND PROCEED on signal in rear of train. Signal indications do not supersede the superiority of trains, therefore, Timetable or Train Order authority is required.

    Absolute Block.- A section of track which may be occupied by only one train or engine at a time.

    Absolute Block Section.- The section of track between opposing Absolute Block SIgnals, at least one block in length, on a track signalled in both directions.

    Automatic Block Signal System.- A series of consecutive blocks governed by block signals, actuated by a train, engine, or by certain conditions affecting the use of a block.

    Manual Block System.- A system used for the blocking of trains moving in the same direction and for which Manual Block rules are in effect.

    Automatic Railroad Crossing System.- An arrangement of fixed signals and signal appliances so interconnected that the movement of trains or engines over the crossing are automatically controlled.

    Traffic Control System (TCS).- An automiatic block signal system under which trains or engines are operated in either direction on one or more tracks under Rule 271.

    Single Direction Signal System (SDSS).- An automatic block signal system under which trains or engines are operated with the current of traffic under Rule D-251.

    Division.- A portion of a railway or railroad designated by timetable.

    Subdivision.- A portion of a division designated by timetable.

    Engine.- A unit propelled by any form of energy, or a combination of such units operated from a single control, used in train or yard service.

    Interlocking.- An arrangement of fixed signals and signal appliances so interconnected that their movements must succeed each other in proper sequence and for which interlocking rules are in effect.

    Interlocking Limits.- The tracks between the opposing absolute signals governing entrance to an interlocking.

    Pilot.- An employe assigned to a train when the Engineer or Conductor, or both, are not fully acquainted with the physical characteristics or rules of the railroad, or portion of the railroad, over which the train is to be moved.