The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1898-06-05
THE INTERL0CRING SYSTEM.
This Railway Feature Described by q
TechnicnI school Student.

The term interlocking usually conveys no
idea TO the mind of person who hears the
name and this Is the more remarkable be-
cause interlocking is one of the most impor-
tant features of railway. 1t is still more
remarkable. the ignorance of the term.
when we consider that at some places trains
go over a crossing at the rate of 600 in TWEEN
ty-four hours, and at times 90 in two hours.
On the Union loop Chicagos elevated rail-
way, this record is surpassed; in the evening
trains follow one another every half minute,
and must be guided by the aid of interlock-
ing 10 their proper tracks. And at a point
twelve miles from Chicago, State line, nine
railroads over which run the trains of elev-
en- companies. cross at one point. The term
interlocking is applied to the entire system
of signaling, and interlocking must not be
confused with Understanding, which is a
different thing.
The necessity for interlocking arose many
years ago. S"-ne years ago, say about thir-
", no inter ng system was in general
use. Up t, time people were not in
such a hui get there and it
thought su snt If a train stopped at
crossing, while trainman went ahead and,
If the other line was clear signaled his train
over the crossing. Besides being slow this
was also dangerous, and the danger became
constantly greater with the growth of rail-
roads. Every train loses at least three
minutes by a stop, and when railroad lines
had become sufficiently numerous, most
States passed Il law that unless a crossing
was protected by some safety device trains
must come to a full top before going over
the crossing; but if the crossing was pro-
tected by some device satisfactory TO the
State Railway Commission trains could
ma at g. IL
time train would lose if it stopped at
every crossing, for between Cincinnati and
Cleveland there are twenty protected cross
ings, and between ST. Louis and Cleveland
twent, EIGHT. So that trains between these
points gain at least an hour per trip by the
use CT interlocking. Thus arose the neceS-
slty OF having one man situated that he
could oversee all approaching trains and
regulate their approach upon the crossing,
to the satisfaction of the railway commits
sion. And with the idea in mind of safety,
speed, ana. therefore, convenience some
body saw that if outlying switches could
be controlled by one man centrally located,
and all signals given by him, matters would
be much improved. England is densey pop
ulated, and therefore has more railroads to
the area than other countries. and it was
in England that interoclSing originated.
building what is called an interlocking
plant, and to the ways the ideas are car
ried out in it. l have here the object chosen
for signaling purposes. Its motions repre-
sent as nearly as possible those of man
who is signaling with his arm to train.
This object is called a semaphore (sign-
bearing) signal. A signal post like this is
set at distance of about four hundred feet
from the crossing. 1t may have only one
arm, or blade, for the main line only, or it
may have two one for the main line and
one for any switches ahead AS before
stated, the movements of this blade re-
semble those of a mans arm. When the
arm is horizontal the meaning is danger,
and no train may pass this signal at dam
ger. All signals like this four hundred feet
from the crossing, are called home, or dam
ger signals.
l have before stated that one OF the OBJ
jects of an interlocking plant is speed. Now
suppose a train 10 be going forty miles an
hour; if the engineer does not know whether
the signal is at danger or clear he will
obviously have to slow up so that there will
be no chance of his running past a danger
signal. But this is contrary to the prin-
ciples of interockng, so a second signal
post is set about 1900 feet in advance OF
the first one This is called the distant
signal. and it serves as an index to the
condition of the home signal. That is. it is
merely a caution signal, and an engineer
may go past it when at caution, but must
slow up
The manipulation of these signals, and OF
the switches, is the next point will con-
slider. Each signal blade is connected to
lever in the tower by means of wires
stretched over small pulleys, and the re-
versing, or throwing of lever, lowers the
blade. BY the use of drawing this move
ment can be shown Before lever can be
reversed other movements take place, which
are as follows To the back of the lever
is attached latch, which in its normal
position holds the lever from moving. When
this latch is raised it moves a number Of
small steel rods about an inch square which
have on them small pieces called dogs.
which fit in corresponding notches in other
bars. These rods and dogs constitute what
is called the locking proper of the machine,
and they may be compared to the rods in a
safe lock, which can only be moved by
certain combination. The principle of the
locking is that when lever is thrown which
allows train on one track to come ahead
no lever can be thrown until the first train
has passed and the first lever has been re-
stored to it's normal position.
The only kind of switches absolutely nee
essary to interlocking is the kind called de-
rails. These are switches which, when
open, simply run a train off the track. They
are about $50 feet from the crossing, and are
controlled from the tower by levers which
are connected to pipe. The derais are for
the purpose of running train off the track
if the engineer goes past danger signal.
And now comes an important feature of the
system. There is a derail home signal
and a distant signal on each side of the
crossing, on every line leading 10 the cross
ing Now what is the connection between
them? Simply stated, II is this: They are
all so interlocked that the derail must be
closed first, then nothing can be moved
but the home signal which works with tho
derail. and then, lastly, the distant signal
can be thrown. And ali levers are so inter-
locked that if one derail is shut, no other
derail in the plant which conflicts with the
first can be shut and absolute safety is
assured, for if one train is allowed TO come
onto the crossing and another train tries TO
come ON at the same time it will run Off
the track before getting to the crossing.
because of the derail, thus avoiding a col
lision between the trains.
With the arrangement an engneman
meets on approaching a crossing. first, dis
tant signal second, home signal; third, de-