Definition of Terms as they are applied to the Rules and
Regulations of the Transportation Department. ABSOLUTE-
PERMISSIVE BLOCK. A block within which the movement of trains on
a desigated section of track or tracks is directed by signals
automatically controlled and without train-order authority and
without superiority of trains. A-PB. Abbreviation for Absolute-
Permissive Block. ABSOLUTE SIGNAL. A home signal, the
indications of which authorize and govern the movement of trains
and engines and supersede the superiority of trains. APPROACH
SIGNAL. A fixed signal used in connection with a home signal to
govern the approach thereto. AUTOMATIC BLOCK SIGNAL SYSTEM. A
series of consecutive blocks governed by block signals actuated
by a train, or by certain conditions affecting the use of a
block. ABS. Abbreviation for Automatic Block Signal System. ATS.
Abbreviation for Automatic Train Stop. BLOCK. A length of track
between consecutive home signals governing in one direction; or
from a home signal to sign reading