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. The English block systems,
however, all employ overlaps. Without the overlap, a train in passing
from one block section to the other will clear the home signals for
the section in the rear, as soon as the rear of the train has passed
the home signal of the block in which it is moving. It is thus
possible for a train to stop within the block and within a few feet of
this home signal. If, then, a following train should for any reason
overrun this home signal, a collision would result. With the overlap
system, however, a train may stop at any point in a block section and
still have the home signal at a safe stopping distance in the rear of
the train.

Conservative signaling is all in favor of the overlap, on account of
the safety factor, in case the signal is accidentally overrun. Another
consideration was the use of automatic train stops. These stops are
placed at the home signals, and it is thus essential that a stopping
distance should be afforded in advance of the home signal to provide
for stopping the train to which the brake had been applied by the
automatic stop.

Ordinarily, the arrangement of overlap sections increases the length
of block sections by the length of the overlap, and as the length of
the section fixed the minimum spacing of trains, it was imperative to
make the blocks as short as consistent with safety, in order not to
cut down the carrying capacity of the railway. This led to a study of
the special problem presented by subway signaling and a development of
a blocking system upon lines which it is believe