This causes disturbances in
the signal-track circuit in proportion to the amount of "drop," and it
was believed that under the extreme condition above mentioned the
ordinary form of track circuit might prove unreliable and cause delay
to traffic. A solution of the difficulty was suggested, consisting in
the employment of a current in the signal track circuit which would
have such characteristic differences from that used to propel the
trains as would operate selectively upon an apparatus which would in
turn control the signal. Alternating current supplied this want on
account of its inductive properties, and was adopted, after a
demonstration of its practicability under similar conditions
elsewhere.
[Illustration: FRONT VIEW OF BLOCK SIGNAL POST, SHOWING LIGHTS,
INDICATORS AND TRACK STOP]
After a decision was reached as to the system to be employed, the
arrangement of the block sections was considered from the standpoint
of maximum safety and maximum traffic capacity, as it was realized
that the rapidly increasing traffic of Greater New York would almost
at once tax the capacity of the line to its utmost.
The usual method of installing automatic block signals in the United
States is to provide home and distant signals with the block sections
extending from home signal to home signal; that is, the block sections
end at the home signals and do not overlap each other. This is also
the arrangement of block sections where the telegraph block or
controlled manual systems are in use.
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