CONDUIT AND SURFACE-CONTACT TRAMWAY SYSTEMS
Roughly speaking, the arrangements for generating electricity,
distributing it, and utilising it on the car, remain the same in
conduit tramways and surface-contact tramways as on the overhead
system. The differences between the three systems are, as already
indicated, confined to the means of collecting the current for each car.
Both the conduit and the surface-contact system were suggested as a
means of escape from the main objection to the overhead system--the
exposure of 'live' wires in the street. The cable tramway, with its
concrete trough and slot, gave an obvious hint. There would be no
difficulty, apparently, in carrying wires on insulators in the trough
or conduit, and utilising the slot for a 'plough' which would slide
along inside the conduit, keeping contact with the wires, and so
conveying the current to the car.
This was tried for the first time in Blackpool, where--in 1884--a
length of conduit tramway was laid along the front street of the town.
The conditions could hardly have been less favourable for the system,
as the sea frequently washed over the roadway, flooding the conduit
with water and sand. Further, the conduit was so shallow that children
were able to get at the conductors with their metal spades. As the
conduit carried the return wire, the effect of a metallic contact
between the two conductors was to cause a 'short circuit,' with very
entertaining fireworks but with no amusing results for the tramway
engineer. After a heroic trial, the system had to be abandoned.
Bournemouth was the next British town to adopt the conduit. It did so
as a token of its exceptional civic pride. Three times, in fact, the
Bournemouth Corporation declared that it did not want tramways of any
kind whatever within its gates. And when the pressure of public opinion
forced its consent, the arrangement was made that no overhead wires
should appear in the central district of the town. Several miles of
conduit tramway were therefore constructed (the trolley system being
used for the outer tramway routes); and as by that time a good deal of
experience had been gained in conduit work both in America and on the
Continent, the contractors were able to give the Corporation a conduit
system built to endure. At first the Corporation was reconciled to the
fact that the conduit sections had cost about twice as much per mile as
the trolley lines, but as years went on, and as the financial results
of the system continued to prove unsatisfactory, the Corporation's
contentment became modified. An examination of the accounts showed that
the conduit sections could be reconstructed on the overhead system at a
cost equal to the annual expense of maintaining these sections in good
working order. Since the public had got used to the overhead wires on
the other sections, and since they had not got used to owning tramways
which produced a heavy loss, the decision was made to abandon the
conduit system altogether.
In London the conduit system was adopted by the London County Council
for various reasons. One was that the Council felt that London ought
to have the best, the very best, and nothing but the best. Another
was that the streets were so congested with traffic, lamp standards,
telegraph and telephone poles, and other obstructions, that trolley
wires and trolley standards would be a great nuisance and a serious
danger. Aesthetic reasons were also advanced, but it is difficult to
realise that they had much weight in connection with the majority of
metropolitan streets. Trolley wires were, in fact, freely erected in
suburban streets where there was a certain amount of beauty worth
preserving.
The main underlying reason, no doubt, was the feeling that London could
afford the most costly system. In any ordinary city (and perhaps in
London as well) the conduit must be regarded as a luxury. It involves
a continuous road excavation so deep that a great deal of incidental
work has frequently to be done in moving gas, water, and drain pipes
out of the way. The conduit itself is a thick channel of concrete,
strengthened at intervals of a few feet with heavy cast iron 'yokes'
which support the 'rails' forming the lips of the slot through which
the 'plough' of the car passes. Elaborate arrangements have to be
made for draining the conduit, as any accumulation of mud or water
in contact with the conductors, or the special insulators supporting
them, would be fatal to the working of the system. And in practice
the ordinary drainage has to be assisted by continual scraping of the
conduit with special brushes and by repeated flushing during the hours
when the cars are not running. Heavy rains and snowstorms are therefore
liable to upset the working of the system; and the tramway manager has
to employ quite an army of men simply to keep the conduit in working
order.
Trouble is also apt to be caused by purely mechanical means. On
one occasion a child's hoop fell through the slot and caused a short
circuit. As the ordinary scrapers slipped over the hoop, its presence
was not detected for a considerable time, during which the tramway
service was at a standstill. Altogether there is a greater liability to
interruption on the conduit system than on the overhead system.
[Illustration: Fig. 5. The upper portion of the illustration shows a
section of a typical conduit system of electric tramway traction.
This section is taken at one of the cast-iron 'yokes' which support
the rails forming the slot through which the 'plough' passes from
the car to make contact with the conductor rails.
The lower illustration gives a longitudinal and transverse section of
the 'G-B.' system of surface-contact tramway traction. The rope-like
cable carries the current and is supported on insulators. When the
collector on the car covers the stud, the action of the magnet draws
the lower part of the stud into contact with the cable, thus supplying
current to the car. After the car has passed, the lower part of the
stud rises by the action of a spring and, breaking contact with the
'live' cable, becomes dead. (In actual practice contact would be made
under the conditions shown in the left-hand diagram.)]
Experience of these drawbacks led the London County Council to seek
an alternative to the conduit when constructing electric lines in the
north of London. Many of the borough councils, following the County
Council's own previous arguments, would not listen to the suggestion
of the overhead system; and a freshly-elected Council, pledged to a
policy of economy, determined to try the surface-contact system. How
this trial gave rise to a violent political controversy, leading to
the abandonment of the project and culminating in important libel
actions, forms a picturesque story which need not be told in detail
here. Its main interest lies, for the moment, in the emphasis which the
incidents give to a characteristic of the surface-contact system--its
sensitiveness to minute alterations in detail.
The surface-contact or 'stud' system is really a modification of the
conduit system. It has, in fact, been called the 'closed conduit.'
The electric wires are again placed in a channel or pipe underground,
but instead of being accessible through a slot, contact can be made
with them only through metal studs placed at intervals flush with the
roadway. By special electro-mechanical devices in the stud and on the
car, the stud is brought into contact with the 'live' underground wire
only when the car is over it. That is to say, the studs covered and
protected by the car will be 'live' and supplying power to the car
through a sliding brush or 'skate,' while those not so protected will
be 'dead' and therefore of no danger to the public.
An immense amount of ingenuity has been expended by many engineers in
devising studs to act with absolute certainty under all conditions.
In the laboratory or the workshop, and even on an experimental track,
it was simple enough to arrange a mechanism which would 'make' and
'break' contact with admirable regularity. But when it came to putting
the mechanism down on an ordinary roadway, to be covered with mud,
pounded by heavy traffic, and subjected to the action of damp, frost,
heat, and all sorts of unexpected influences, much less satisfactory
results were obtained. Time and again the hopes of engineers were
dashed by a succession of petty troubles--some of them obscure, most
of them unforeseen. The weak points in nearly all the systems were the
insulation of electrical parts and the road construction work. Lack
of simplicity and rigidity led to the introduction of moisture and to
the shifting of parts so that studs jammed and remained 'alive' after
the car had passed over them. But even after the practical elimination
of these troubles the success of the surface-contact system seemed as
sensitive as the system itself.
One system was tried at Torquay, and discontinued after a protracted
trial on a large scale. Another system--the Lorain system--was
installed at Wolverhampton and is still in operation, but without
imitators. A third system--the Griffiths-Bedell or G-B. system--was
installed in 1905 at Lincoln, with satisfactory results. It was the
G-B. system which was offered to the metropolitan borough councils as
an alternative to the conduit and the trolley. A trial section was
laid down in 1898 in the Bow Road, and a certain amount of trouble was
experienced with live studs and with various parts of the equipment.
Owing to the stud system having been suggested by the Moderate Party,
the experimental difficulties were extensively advertised by members
of the Progressive Party, who condemned the system as dangerous and
unworkable. Public feeling was worked up to such a pitch that, in the
face of expert advice in favour of the system in a somewhat modified
form, the Council decided to abandon the experiment. Libel actions by
the owners of the 'G-B.' patents followed, part of the plaintiffs' case
being that the system as laid down was altered in a number of small but
vitally important details by the Council's officers and was therefore
not the 'G-B.' system proper.
The results with the 'G-B.' system at Lincoln prove that it is
possible to construct surface-contact tramways at a cost about 10 per
cent. more than that of trolley tramways, and to operate them, safely
and with reliability, at a cost not appreciably more than the general
working expenses of an overhead line. But this proof has not only been
enfeebled for the special reasons just described, but it came at a time
when the public had got quite accustomed to the trolley and also when
most towns had already been equipped with electric traction. Ten or
fifteen years earlier, such a proof might have changed the course of
tramway development; now it can have no great material effect.
The upshot of the contest between the three systems has, therefore,
been the survival of the one which was most despised at the outset.