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Train control is the process by which the movement
of rail rapid transit vehicles is regulated for
the purposes of safety and efficiency. The process is
carried out by a combination of elements-some
men, some machines—located on the train, along
the track, in stations, and at remote central
facilities. These elements interact to form a command
and control system with four major functions:
. Train Protection prevention of collisions
and derailments,
. Train Operation control of train
movement an d
stopping at stations,
● Train Supervision direction of train
movement in relation
to schedule,
. Communication interchange of information
among
the elements of the
system.
The train control system is analogous to the sensory
organs and central nervous system of the
human body. It senses and processes information,
makes decisions, and transmits commands. Also as
in the human body, the execution of commands is
not a function of the train control system but of
other parts specialized for that purpose. For example,
the train control system may sense train speed,
determine that it should be increased, provide an
appropriate command signal to the motors, and
monitor to see that the desired result is achieved.
The means by which a speed change is effected,
however, are not part of the train control system.
All the equipment for getting electric power to the
wayside, bringing it into the train, converting it to
mechanical energy, and providing tractive effort is
external to the train control system. Similarly, the
equipment to select a route for a particular train and
transmit commands to aline switches accordingly
are within the train control system, but the parts of
the trackwork that actually move (the switch
points) are not elements of the train control system.
TRAIN CONTROL
SYSTEM FUNCTIONS
Presented below is a description of the specific
functions performed by a train control system and of the way in which functional elements interact.
These functional relationships are also illustrated
by the diagram in figure 1. Since the purpose is only
to provide the reader with a general background for
understanding the nature of train control, the
definitions presented here are brief and nontechnical.8
Train Protection
Train protection is a family of functions whose
purpose is to assure the safety of train movement by
preventing collisions and derailments. 9 rain protection
functions and requirements override all
other control system functions either through
equipment design or, in a completely manual mode,
by rules and procedures. The functions that make
up train protection are:
Train detection—monitoring of the track to
determine the presence and location of trains;
Train separation-assuring that trains on the
same track maintain a safe following distance
to prevent collisions;
Route interlocking—preventing trains on crossing,
merging, or branching routes from making
conflicting (unsafe) moves that would cause a
collision or derailment;
Overspeed protection—assuring that train
speed remains at or below the commanded or
posted civil speed limit10 as to prevent collisions
resulting from going too fast to stop
within the available distance and to prevent=
derailments due to excessive speed on curves
or through switches;
Train and track surveillance-observing conditions
on and in the vicinity of the track ahead
of the train and monitoring safety-related conditions
on board the train.
Train Operation
Train operation consists of those functions
necessary to move the train and to stop it at stations