be double this or 1394 feet.
The average length of overlaps, as laid out, is about 800 feet, and
the length of block sections double this, or 1,600 feet.

[Illustration: VIEW UNDER CAR, SHOWING TRIGGER ON TRUCK IN POSITION TO
ENGAGE WITH TRACK STOP]

The protection provided by this unique arrangement of signals is
illustrated on page 143. Three positions of train are shown:

"A." MINIMUM distance between trains: The first train has
just passed the home signal, the second train is stopped by
the home signal in the rear; if this train had failed to stop
at this point, the automatic stop would have applied the air
brake and the train would have had the overlap distance in
which to stop before it could reach the rear of the train in
advance; therefore, under the worst conditions, no train can
get closer to the train in advance than the length of the
overlap, and this is always a safe stopping distance.

"B." CAUTION distance between train: The first train in same
position as in "A," the second train at the third home signal
in the rear; this signal can be passed under caution, and
this distance between trains is the caution distance, and is
always equal to the length of the block section, or two
overlaps.

"C." CLEAR distance between trains: First train in same
position as in "A," second train at the fourth home signal in
the rear; at this point both the home and distant signals are
clear, and the distance between the trains is now the clear
running distance; that is, when the trains are one block
section plus an overlap apart they can move under clear
signal, and this distance is used in determining the running
schedule. It will be noted in "C" that the first train has
the following protection: Home signals 1 and 2 in stop
position, together with the automatic stop at signal 2 in
position to stop a train, distant signal 1, 2, and 3 all at
caution, or, in other words, a train that has stopped is
always protected by two home signals in its rear, and by
three caution signals, in addition to this an automatic stop
placed at a safe stopping distance in the rear of the train.

[Illustration: ELECTRO-PNEUMATIC INTERLOCKING MACHINE ON STATION
PLATFORM]

[Illustration: SPECIAL INTERLOCKING SIGNAL CABIN SOUTH OF BROOKLYN
BRIDGE STATION]

[Sidenote: _Description
of Block
Signaling
System_]

The bloc