Railroads

3915

Railroads

struction is on the track or a rail is broken,
the current is broken or ceases to flow through
the relay magnet and the signal goes to
'stop' the same as if a train was in the block.
The ordinary type of signal used in auto-
matic block signaling was formerly the
semaphore. This gives indications by its
position. The blade of arm is about 4 ft.
long and 8 inches wide. It is pivoted at
one end and is carried on a post about 20
ft. above the rails to the right of, or on, a
signal bridge over the track it controls. The
pivot carries a counterweight or spectacle
casting in which red, yellow and green
lenses are mounted and behind which is
placed a lamp for giving night indications.
The arm moves in either the upper or lower
right-hand quadrant. When the blade is in

or in thick weather. In most cases in such
installations colored lights are used as in
ordinary street traffic signals.

Interlocking signals, at junctions and cross-
overs, are those which are made to work in
connection with the shifting parts of rail-
road track, such as moveable frogs and
switches. They are so arranged that, first, no
train shall proceed until all of the tracks
and movable parts have been placed in their
proper positions; second, no train shall pro-
ceed until all other trains which might collide
with it have been warned to stop; third,
none of the shifting parts of the track can be
moved so long as a signal gives an indication
to proceed. Power locking, in its essential
principles, is similar to the manual or me-
chanical interlocking described above. The

Courtesy General Railway Signal Co.

Electric Interlocking Plant at Cleveland Union Terminal.

the horizontal position the signal shows red
at night and indicates stop. If moving in
the upper quadrant when vertical or if in
the lower quadrant, when at the lowest posi-
tion the blade gives a clear indication and
the light shows green. The middle position
in the upper quadrant indicates caution and
shows a yellow light. With lower quadrant
signals a separate arm is used for the caution
indication, The movement of the ram to the
caution or proceed position, as controlled by
the track circuit relay above described, is
effected by a motor, actuated usually by cur-
rent from storage batteries sunk in a well at
the foot of the signal post. Movement to the
horizontal or stop-position is by gravity.
In recent installations or replacements, the
tendency has been to replace the semaphores
by light signals. These use strong lights and
reflectors of sufficient power to be visible in
the brightest sunlight* Such signals give
much clearer indications, especially at night

locking features of the machine are much the
same, but, in place of the manual levers con-
nected to the signals and switches by wires
and pipes, electric control is used, the signals
and switches being controlled by electric cur-
rent in either case but actuated by com-
pressed air in the electric-pneumatic system
and by electric motors in the all-electric sys-
tem. Several interesting adaptations of inter-
locking, particularly in relation to automatic
block signals, have been introduced in recent
years. One is the automatic interlocking sys-
tem used for a crossing of one road by an-
other at a point where the number of trains
is limited. By means of crack circuits, a train
moving to the crossing moves the signals to
clear on its own track if the other track is
not occupied, and moves across the crossing
protected by the stop signals on the other
track. Remote power switches have rapidly
come into more general use. These are
switches located possibly several miles from