The above, I admit, is a very brief summary of an immense and complex
subject, namely, the bridging of the gap which exists between the
producer and the arterial railway, or the producer and his market, if it
be a distant one. Ruling out pack and porter as being too uneconomical
to be used on a large scale, we are left with the wagon, the lorry and
the light railway. All these three means can cover great distances, but
they do not solve the problem, because the solution does not only lie in
power to traverse distance, but in ability to cover the largest area in
the shortest time.
The difficulty so far has been that the wheel demands a road and
destroys a road, and that, whilst it is easy, though frequently very
costly, to make a road which will suit a wheel, it is most difficult to
make a wheel which will not damage a road; for failing a cheap and
simple form of Pedrail wheel, a system of multi-wheels has to be
resorted to, and this system leads directly to the tracked machine,
which not only can dispense with roads, but, what is equally important,
can make its own track, just as the feet of a man form a path by
frequently crossing the same piece of ground.
This is not the place to examine in detail the technicalities of
roadless vehicles; but to-day there are two main types of these
vehicles; an all-tracked machine of the tank type, and a half-tracked
machine which has wheels in front and tracks in rear. The first is more
suitable for heavy loads, and the second for light.
In the manufacture of these vehicles three main problems must be solved:
(1) The vehicle must be able to use roads without damaging them; nor
must it damage the surface of the ground it travels over.
(2) It must be able to move across country without damaging itself.
(3) The cost per ton-mile must be equal or lower than that of existing
vehicles.
It may seem a paradox to lay down that the first requirement of a
roadless vehicle is that it can negotiate roads, but, in fact, it is not
so; for it stands to reason that, when prepared tracks do exist, it is
only wasting time and energy to travel across country. Further, if the
tracks of the vehicle are so constructed that they do not damage roads,
they will not damage the surface of the ground, and, consequently, by
continually travelling over the same ground, they will compact and
consolidate its surface and rapidly form a road of their own which will
require no metalling. This advantage is one of the great secrets of its
success.
As movement across country entails traversing rough ground, the tracks
of a roadless vehicle must permit of the absorption of obstacles. This
absorption is attained by springing the tracks. In an unsprung machine,
obstacles are either crushed into the ground or the vehicle has to lift
itself over them. In both cases the result is injury to the machine, and
loss of power and discomfort.
It stands to reason that the vehicle must be durable, simple and easy to
maintain; also that the ton-mile cost must be low. As regards this
latter requirement, experimental machines have so far proved that this
is a possibility. A one-ton roadless Guy Lorry recently travelled from
London to Aldershot, and its ton mileage was fifty-two to the gallon. It
has also been worked out that the cost per ton-mile of the Sentinel
tractor, “including overhead charges, depreciation, interest on capital
and all running charges, and allowing for a 20-tons net load for a
reasonable number of working days in the year,” will be slightly under
twopence per ton-mile.
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