RAILROAD ACCIDENTS.
182
CHAPTER XVIII.
INTERLOCKING.
IN their management of switches, especially at points of railroad
convergence where a heavy traffic is concentrated and the passage
of trains or movement of cars and locomotives is unceasing, the
English are immeasurably in advance of the Americans; and, indeed,
of all other people. In fact, in this respect the American managers
have shown themselves slow to learn, and have evinced an indisposition
to adopt labor-saving appliances which, considering their usual
quickness of discernment in that regard, is at first sight inexplicable.
Having always been accustomed to the old and simple methods, just
so long as they can through those methods handle their traffic
with a bearable degree of inconvenience and expense, they will
continue to do so. That their present method is most extravagant,
just as extravagant as it would be to rent two houses or to run
two steam engines where one, if properly
THE CANNON STREET STATION. 183
used, could be made to suffice, admits of demonstration;but
the waste is not on the surface, and the necessity for economy
is not imperative. The difference of conditions and the difference
in results may be made very obvious by a comparison. Take, for
instance, London and Bostonthe Cannon street station in
the one and the Beach street station in the other. The concentration
of traffic at London is so great that it becomes necessary to
utilize every foot of ground devoted to railroad purposes to the
utmost possible extent. Not only must it be packed with tracks,
but those tracks must never be idle. The incessant train movement
at Cannon street has already been referred to as probably the
most extraordinary and confusing spectacle in the whole wide circle
of railroad wonders. The result is that in some way, at this one
station and under this single roof, more trains must daily be
made to enter and leave than enter and leave, not only the Beach
street station, but all the eight railroad stations in Boston
combined.*
* "It has been estimated that an average
of 50,000 persons were, in 1869, daily brought into Boston and
carried from it, on three hundred and eighty-five trains, while
the South Eastern railway of London received and despatched in
1870, on an average, six hundred and fifty trains a day, between
6 A.m. and 12 P.M. carrying from 35,000 to 40,000 persons, and
this too without the occurrence of a single train accident during
the year. On one single exceptional day eleven hundred and eleven
trains, carrying 145,000 persons, are said to have entered and
left this station in the space of eighteen hours."Third
Annual Report, [18721 of Massachusetts Railroad Commissioners,
P.141.
The passenger movement over the roads terminating
in Boston was probably as heavy on June 17, 1875, as during any
twenty-four hours in their history. It was returned at 280,000
persons carried in 641 trains. About twice the passenger movement
of the "exceptional day" referred to, carried in something
more than half the number of trains, entering and leaving eight
stations instead of one.
184 RAILROAD ACCIDENTS.
During eighteen successive hours trains have been made to enter
and leave this station at the rate of more than one in each minute.
It contains four platforms and seven tracks, the longest of which
is 720 feet. As compared with the largest station in Boston (the
Boston & Providence), it has the same number of platforms
and an aggregate of 1,500 (three-fifths) more feet of track under
cover; it daily accommodates about nine times as many trains and
four times as many passengers. Of it Barry, in his treatise on
Railway Appliances (P. 197), says: "The platform area at
this station is probably minimised but, the station accommodates
efficiently a very large mixed traffic of long and short journey
trains, amounting at times to as many as 400 trains in and 400
trains out in a working day.*"
The American system is, therefore, one of great waste; for,
being conducted in the way it is-that is with stations and tracks
utilized to but a fractional part of their utmost capacity it
requires a large number of stations and tracks and the services
of many employees. Indeed it is safe to say that,
* The Grand Central Depot on 42d Street in
New York City, has nearly twice the amount of track room under
cover of the Cannon street station. The daily train movement of
the latter would be precisely paralleled in New York, though not
equalled in amount, if the 42d street station were at Trinity
church, and, in addition to the trains which now enter and leave
it, all the city trains of the Elevated road were also provided
for there.
PRIMITIVE WAYS 185
judged by the London standard, not more than two of the eight-stations
in Boston are at this time utilized to above a quarter part of
their full working capacity; and the same is probably true of
all other American cities. Both employees and the travelling public
are accustomed to a slow movement and abundance of room; land
is comparatively cheap, and the pressure of concentration has
only just begun to make itself felt. Accordingly any person, who
cares to pass an hour during the busy time of day in front of
an American city station, cannot but be struck, while watching
the constant movement, with the primitive way in which it is conducted.
Here are a multiplicity of tracks all connected with each other,
and cars and locomotives are being passed from one to another
from morning to night. A constant shifting of switches is going
on, and the little shunting engines never stand still. The switches,
however, as a rule, are unprovided with signals, except of the
crudest description; they have no connection with each other,
and during thirty years no change has been made in the method
in which they are worked. When one of them has to be shifted,
a man goes to it and shifts it. To facilitate the process, the
monitor shunting engines are provided with a foot-board in front
and behind, just above the track, upon which the yard hands jump,
and are carried about from switch to switch, thus saving the time
they would occupy if they had to walk. A simpler arrangement could
186 RAILROAD ACCIDENTS.
not be imagined; anyone could devise it. The only wonder is
that even a considerable traffic can be conducted safely in reliance
upon it.
Turning from Beach to Cannon street, it is apparent that the
train movement which has there to be accommodated would fall into
inextricable confusion if it was attempted to manage it in the
way which has been described. The number of trains is so great
and the movement so rapid and intricate, that not even a regiment
of employees stationed here and there at the signals and switches
could keep things in motion. From time to time they would block,
and then the whole vast machine would be brought to a standstill
until order could be reestablished. The difficulty is overcome
in a very simple way, by means of an equally simple apparatus.
The control over the numerous switches and corresponding signals,
instead of being divided up among many men stationed at many points,
is concentrated in the hands of two men occupying a single gallery,
which is elevated across the tracks in front of the station and
commanding the approaches to it, much as the pilot-house of an
American steamer commands a view of the course before it. From
this gallery, by means of what is known as the interlocking system,
every switch and signal in the yard below is moved; and to such
a point of perfection has the apparatus been carried, that any
disaster from the misplacement of a switch or the display of a
wrong signal is rendered impossible. Of this Cannon
THE ORIGIN OF INTERLOCKING. 187
street apparatus Barry says, "there are here nearly seventy
point and signal levers concentrated in one signal house; the
number of combinations which would be possible if all the signal
and point levers were not interlocked can be expressed only by
millions. Of these only 808 combinations are safe, and by the
interlocking apparatus these 808 combinations are rendered possible,
and all the others impossible."*
It is not proposed to enter at any length into the mechanical
details of this appliance, which, however, must be considered
as one of the three or four great inventions which have marked
epochs in the history of railroad traffic.+ As, however, it is
but little known in America, and will inevitably within the next
few years find here the widest field for its increased use, a
slight sketch of its gradual development and of its leading mechanical
features may not be out of place. Prior to the year 1846 the switches
and signals on the English roads were worked in the same way that
they are now commonly worked in this country. As a train drew
near to a junction, for instance, the switchman stationed there
made the proper track connection and then displayed the signal
which indicated what tracks were opened and what closed, and which
line had the right of way;
* Railway Appliances, p. I 13.
+ A sufficiently popular description of this
apparatus also, illustrated by cuts, will be found in Barry's
excellent little treatise on Railway Appliances, already
referred to, published by Longmans & Co. as one of their series
of text-books of science.
188 RAILROAD ACCIDENTS.
and the engine-drivers acted accordingly. As the number of
trains increased and the movement at the junctions became more
complicated, the danger of the wrong switches being thrown or
the wrong signals displayed, increased also. Mistakes from time
to time would happen, even when only the most careful and experienced
men were employed; and mistakes in these matters led to serious
consequences. It, therefore, became the practice, instead of having
the switch or signal lever at the point where the switch or signal
itself was, as is still almost universally the case in this country,
to connect them by rods or wires with their levers, which were
concentrated at some convenient point for working, and placed
under the control of one man instead of several. So far as it
went this change was an improvement, but no provision yet existed
against the danger of mistake in throwing switches and displaying
signals. The blunder of first making one combination of tracks
and then showing the signal for another was less liable to happen
after the concentration of the levers under one hand than before,
but it still might happen at any time, and certainly would happen
at some time. If all danger of accident from human fallibility
was ever to be eliminated a far more complicated mechanical apparatus
must be devised. In response to this need the system of interlocking
was gradually developed, though not until about the year 1856
was it brought to any considerable degree of perfection. The whole
THE ELIMINATATION OF BLUNDERS. 189
object of this system is to render it impossible for a switchman,
whether because he is weary or agitated or actually malicious
or only inexperienced, to give contrary signals, or to break his
line in one way and to give the signal for its being broken in
another way. To bring this about the levers are concentrated in
a cabin or gallery, and placed side by side in a frame, their
lower ends connecting with the switch-points and signals by means
of rods and wires. Beneath this frame are one or more long bars,
extending its entire length under it and parallel with it. These
are called locking bars; for, being moved to the right or left
by the action of the levers they hold these levers in certain
designated positions, nor do they permit them to occupy any other.
In this way what is termed the interlocking is effected. The apparatus,
though complicated, is simplicity itself compared with a clock
or a locomotive. The complication, also, such as it is, arises
from the fact that each situation is a problem by itself, and
as such has to be studied out and provided for separately. This,
however, is a difficulty affecting the manufacturer rather than
the operator. To the latter the apparatus presents no difficulty
which a fairly intelligent mechanic cannot easily master; while
for the former the highly complicated nature of the problem may,
perhaps, best be inferred from the example given by Mr. Barry,
the simplest that can offer, that of an ordinary junction where
a double-track branch-road connects with
190 RAILROAD ACCIDENTS.
its double-track main line. There would in this case be of
necessity two switch levers and four signal levers, which would
admit of sixty-four possible combinations. "The signal might
be arranged in any of sixteen ways, and the points might occupy
any of four positions, irrespective of the position of the signals.
Of the sixty-four combinations thus possible only thirteen are
safe, and the rest are such as might lure an engine-driver into
danger."
Originally the locking bar was worked through the direct action
of certain locks, as they were called, between which the levers
when moved played to and fro. These locks were mere bars or plates
of iron, some with inclined sides, and others with sides indented
or notched. At one end they were secured on a pivot to a fixed
bar opposite to and parallel with the movable locking bar, while
their other ends were made fast to the locking bar; whence it
necessarily followed that, as certain of the levers were pushed
to and fro between them, the action of these levers on the inclined
sides of the locks could by a skilful combination be made to throw
other levers into the notches and indentations of other locks,
thus securing them in certain positions, and making it impossible
for them to be in any other positions.
The apparatus which has been described, though a great improvement
on anything which had preceded it, was still but a clumsy affair,
and naturally
THE SPRING CATCH-ROD. 191
the friction of the levers on the locks was so great that they
soon became worn, and when worn they could not be relied upon
to move the switch-points with the necessary accuracy. The new
appliance of safety bad, therefore, as is often the case, introduced
a new and very considerable danger of its own. The signals and
switches, it was true, could no longer disagree, but the points
themselves were sometimes not properly set, or, owing to the great
exertion required to work it, the interlocking gear was strained.
This difficulty resulted in the next and last improvement, which
was a genuine triumph of mechanical ingenuity. To insure the proper
length of stroke being made in moving the leverthat is to
make it certain in each case that the switch points were brought
into exactly the proper positiontwo notches were provided
in the slot, or quadrant, as it is called, in which the lever
moved, and, when it was thrown squarely home, and not until then,
a spring catch caught in one or other of these notches. This spring
was worked by a clasp at the handle of the lever, and the whole
was called the spring catch-rod. By a singularly ingenious contrivance,
the process of interlocking was transferred from the action of
the levers and the keys to these spring catch-rods, which were
made to work upon each other, and thus to become the medium through
which the whole process is effected. The result of this improvement
was that, as the switchman cannot move any lever until the spring
192 RAILROAD ACCIDENTS.
catch rod is fastened, except for a particular movement, he
cannot, do what he will, even begin any other movement than that
one, as the levers cannot be started. On the other hand, it may
be said that, by means of this improvement, the mere "intention
of the signal-man to move any lever, expressed by his grasping
the lever and so raising the spring catch-rod, independently of
his putting his intention in force, actuates all the necessary
locking.*"
* In regard to the interlocking system as then
in use in England, Captain Tyler in his report as head of the
railway inspecting department of the Board of Trade, used the
following language in his report on the accidents during 1870.
"When the apparatus is properly constructed and efficiently
maintained, the signalman cannot make a mistake in the working
of his points and signals which shall lead to accident or collision,
except only by first lowering his signal and switching his train
forward, then putting up his signal again as it approaches, and
altering the points as the driver comes up to, or while he is
passing over them. Such a mistake was actually made in one of
the cases above quoted. It is, of course, impossible to provide
completely for cases of this description; but the locking apparatus,
as now applied, is already of enormous value in preventing accidents;
and it will have a still greater effect on the general safety
of railway travelling as it becomes more extensively applied on
the older lines. Without it, a signalman in constantly working
points and signals is almost certain sooner or later to make a
mistake, and to cause an accident of a more or less serious character;
and it is inexcusable in any railway company to allow its mail
or express trains to run at high speed through facing points which
are not interlocked efficiently with the signals, by which alone
the engine-drivers in approaching them can be guided. There is
however, very much yet to be effected in different parts of the
country in this respect. And it is worth while to record here,
in illustration of the difficulties that are sometimes met with
by the inspecting officers, that the Midland Railway Company formally
protested in June, 1866, against being compelled to apply such
apparatus before receiving sanction for the opening of new lines
of railway. They stated that in complying with the requirements
in this respect of the Board of Trade, they 'were acting in
direct opposition to their own convictions, and they must, so
far as lay in their power, decline the responsibility of the locking
system.' "
To still further perfect the appliance a simple
mechanism has since 1870 been attached to the rod actuating the
switch-bolt, which prevents the signal-man from shifting the switch
under a passing train in the manner suggested by Captain Tyler
in the above extract. In fact it is no exaggeration to say that
the interlocking system has now been so studied, and every possible
contingency so thoroughly provided for, that in using it accidents
can only occur through a willful intention to bring them about.
DOES IT WORK? 193
In spite of any theoretical or fanciful objections which may
be urged against it, this appliance will be found an indispensable
adjunct to any really heavy junction or terminal train movement.
For the elevated railroads of New York, for instance, its early
adoption proved a necessity. As for questions of temperature,
climate, etc., as affecting the long connecting rods and wires
which are an essential part of the system, objections based upon
them are purely imaginary. Difficulties from this source were
long since met and overcome by very simple compensating arrangements,
and in practice occasion no inconvenience. That rods may break,
and that wires are at all times liable to get out of gear, every
one knows; and yet this fact is urged as a novel objection to
each new mechanical improvement. That a broken or disordered apparatus
will always occasion a serious disturbance to any heavy train
movement, may also be admitted. The fact none the less remains
that in practice, and daily subjected through long periods of
time to incomparably the heaviest train movement known to railroad
experience, the rods of the interlocking apparatus do not break,
nor do it's wires get out of
194 RAILROAD ACCIDENTS.
gear; while by means of it, and of it alone, this train movement
goes unceasingly on never knowing any serious disturbance.*
It is not, however, alone in connection with terminal stations
and junctions that the interlocking apparatus is of value. It
is also the scientific substitute for the law or regulation compelling
trains to stop as a measure of precaution when they approach grade-crossings
or draw-bridges. It is difficult indeed to pass from the consideration
of this fine result of science and to speak with patience of the
existing American substitute for it. If the former is a feature
in the block system, the latter is a signal example of the block-head
system. As a device to avoid danger it is a standing disgrace
to American ingenuity; and, fortunately, as stopping is compatible
only with a very light traffic, so soon. as the passage of trains
becomes incessant a substitute for it has got to be devised. In
this country,
* "As an instance of the possibility of
preventing the mistakes so often made by signal men with conflicting
signals or with facing points I have shown the traffic for a single
day, and at certain hours of that day, at the Cannon Street station
of the South Eastern Railway, already referred to as one of the
no-accident lines of the year. The traffic of that station,
with trains continually crossing one another, by daylight and
in darkness, in fog or in sunshine, amounts to more than 130 trains
in three hours in the morning, and a similar number in the evening;
and, altogether, to 652 trains, conveying more than 35,000 passengers
in the day as a winter, or 40,000 passengers a day as a summer
average. It is probably not too much to say, that without the
signal and point arrangements which have there been supplied,
and the system of interlocking which has there been so carefully
carried out, the signalmen could not carry on their duties for
one hour without accident." Captain Tyler's report on
accidents for 1870, p. 35.
SWING-BRIDGES AND GRADE-CROSSINGS. 195
as in England, that substitute will be found in the interlocking
apparatus. By means of it the draw-bridge, for instance, can be
so connected with the danger signals-which may, if desired, be
gates closing across the railroad tracks-that the one cannot be
opened except by closing the other. This is the method adopted
in Great Britain not only at draws in bridges, but frequently
also in the case of gates at level road crossings. It has already
been noticed that in Great Britain accidents at draws in bridges
seem to be unknown. Certainly not one has been reported during
the last nine years. The security afforded in this case by interlocking
would, indeed, seem to be absolute; as, if the apparatus is out
of order, either the gates or the bridge would be closed, and
could not be opened until it was repaired. So also as respects
the grade-crossing of one railroad by another. Bringing all trains
to a complete stop when approaching these crossings is a precaution
quite generally observed in America, either as a matter of statute
law or running regulation; and yet during the six years 1873-8
no less than 104 collisions were reported at these crossings.
In Great Britain during the nine years I870-8 but nine cases of
accidents of this description were reported, and in both the years
1877 and 1878 under the head of "Accidents or Collisions
on Level Crossings of Railways," the chief inspector of the
Board of Trade tersely stated that," No accident was
inquired into under this
196 RAILROAD ACCIDENTS.
head.* "The interlocking system there affords the most
perfect protection which can be devised against a most dangerous
practice in railroad construction to which Americans are almost
recklessly addicted. It is, also, matter of daily experience that
the interlocking system does afford a perfect practical safeguard
in this case. Every junction of a branch with a double track road
involves a grade-crossing, and a grade-crossing of the most dangerous
character. On the Metropolitan Elevated railroad of New York,
at 53d street, there is one of these junctions, where, all day
long, trains are crossing at grade at the rate of some twenty
miles an hour. These trains never stop, except when signalled
so to do. The interlocking apparatus, however, makes it impossible
that one track should be open except when the other is closed.
An accident, therefore, can happen only through the willful carelessness
of the engineer in charge of a train;and in the face of
willful carelessness laws are of no more avail than signals. If
a man in control of a locomotive wishes to bring on a collision
he can always do it.
* "As affecting the safe working of railways,
the level crossing of one railway by another is a matter of very
serious import. Even when signalled on the most approved principles,
they are a source of danger, and, if possible, should always be
avoided. At junctions of branch or other railways the practice
has been adopted by some companies in special cases, to carry
the off line under or over the main line by a bridge. This course
should generally be adopted in the case of railways on which the
traffic is large, and more expressly where express and fast trains
are run." Report on Accidents on Railways of the United
Kingdom during 1877,.P. 35.
GIVE SCIENCE A CHANCE! 197
Unless he wishes to, however, the interlocking apparatus not
only can prevent him from so doing, but as a matter of fact always
does. The same rule which holds good at junctions would hold good
at level crossings. There is no essential difference between the
two. By means of the interlocking apparatus the crossing can be
so blocked at any desired distance from it in such a way that
when one track is open the other must be closed;unless,
indeed, the apparatus is out of order, and then both would be
closed. The precaution in this case, also, is absolute. Unlike
the rule as to stopping, it does not depend on the caution or
judgment of individuals;there are the signals and the obstructions,
and if they are not displayed on one road they are on the other.
So superior is this apparatus in every respectas regards
safety as well as convenienceto the precaution of coming
to a stop, that, as an inducement to introduce an almost perfect
scientific appliance, it would be very desirable that states like
Massachusetts and Connecticut compelling the stop, should except
from the operation of the law all draw-bridges or grade-crossings
at which suitable interlocking apparatus is provided. Surely it
is not unreasonable that in this case science should have a chance
to assert itself.
In any event, however, the general introduction of the interlocking
apparatus into the American railroad system may be regarded as
a mere question of the value of land and concentration of traffic.
So long as every road terminating in our larger cities
198 RAILROAD ACCIDENTS.
indulges, at whatever unnecessary cost to its stockholders,
in independent station buildings far removed from business centres,
the train movement can most economically be conducted as it now
is. The expense of the interlocking apparatus is avoided by the
very simple process of incurring the many fold heavier expense
of several station buildings and vast disconnected station grounds.
If, however, in the city of Boston, for instance, the time should
come when the financial and engineering audacity of the great
English companies shall be imitated,when some leading railroad
company shall fix its central passenger station on Tremont street
opposite the head of Court street, just as in London the South
Eastern established itself on Cannon street, and then this company
carrying its road from Pemberton Square by a tunnel under Beacon
Hill and the Statehouse should at the crossing of the Charles
radiate out so as to afford all other roads an access for their
trains to the same terminal point, thus concentrating there the
whole daily movement of that busy population which makes of Boston
its daily counting-room and market-place,then, when this
is attempted, the time will have come for utilizing to its utmost
capacity every available inch of space to render possible the
incessant passage of trains. Then also will it at last be realized
that it is far cheaper to use a costly and intricate apparatus
which enables two companies to be run into one convenient station,
than it is to build a separate station, even at an in. convenient
point, to accommodate each company.
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