Problems of the
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HAULIER
and
CARRIER
NOW I pass to the consideration of a phase of trailer use entirely different from that with which I have hitherto been dealing. With a steam wagon and trailer, or a petrol lorry and trailer—the two are one in principle—the hauling vehicle also carries a load and can be used independently for that purpose, that is to say, whether the trailer be attached or not. The trailer is, in a sense, an auxiliary or supplementary unit and, in the majority of cases, is best regarded in that light.
Now I want to discuss the use of a trailer, or several trailers, in conjunction with a tractor—a non-loadbearing machine.
The first factor to consider is the legal aspect. I showed, in dealing with the case of the steam wagon and trailer, that the operation of the Road Traffic Act, 19341 would encourage the use of trailers, or, at any rate, should do so, so soon as its provisions began to be generally understood. I think it should offer even greater encouragement to the use of tractor-trailer combinations. I do not think that effect was ,in the
minds of those ivho drafted the Bill. Indeed, the reverse was the case, for. the intention was to discourage the employment of trailers. However, let us examine the position.
A motor tractor, according to the Act, is a mechanically propelled vehicle which itself is not constructed to carry any load other than water, fuel, accumulators and other equipment used for the purpose of propulsion, loose tools and equipment, and the unladen weight of wfiich does not exceed 71 tons.
That is a plain definition of a simple and straightforward type of tractor. It does not, however, cover B44 all those types of mechanically propelled vehicle which operate as tractors and which, so far as the user is concerned, may appear to be tractors, neither more nor less. For a complete understanding of the practical application of the term it is necessary to consider those forms of tractor which are constructed so that a small portion of the load of the trailer is superimposed upon them.
This distinction between the two designs is most important, as may be realized when we come to consider the question of speed limits. The words of the Act in this connection are: " That the maximum speed of a motor tractor when not drawing a trailer, if all the wheels of the tractor be equipped with soft or elastic tyres, shall be 16 m.p.h. and the maximum speed of a motor tractor when drawing a trailer, if all the wheels, both of the tractor and of any trailer drawn by-it, be equipped with soft or elastic tyres, shall be 8 m.p.h.."
There is no definite or direct provision in the speedlimit schedule for a tractor and trailer equipped with pneumatic tyres, which is a curious omission. It is necessary just here to interpolate a reference to the speed of -a heavy motor vehicle when drawing a trailer. In such a case, as I have already disclosed in discussing the steam wagon and trailer proposition : "If all the wheels' both of the drawing vehicle and of the trailer be equipped with pneumatic tyres . . . ." the maximuni limit of speed is 16 m.p.h. The position is, therefore, a peculiar one. It seems as though a tractor pure and simple may not, when it is drawing a trailer, travel at more than 8 m.p.h., but ' If it can be trangferred to that class of vehicle which itself carries a load as well as hauls a trailer, then, if it be on pneumatic tyres, its legal speed may be increased to 16 m.p.h. a It almost seems as though, if the method of coupling between a tractor unit and a trailer be such that a certain amount of weight is superimposed so that the tractor is then actually carrying a load, it need not, for our present purpose, be considered lobe a tractor, but falls within the category of vehicles carrying loads.
Here, it becomes necessary to distinguish between
tractor and trailer combinations and articulated vehicles. The latter type of machine is indicated in the Act by that definition given in sub-section 4 of Section 2, Part 1, which states that "In any ease where a motor vehicle is so constructed that a trailer may by partial superimposition be attached to the vehicle in such a manner as to cause a substantial part of the weight of, the trailer to be borne by the vehicle', that vehicle shall be deemed to be a vehicle itself constructed to carry a load." (The italics are mine.)
It seems, therefore, that if too great a proportion of the weight of the trailer be superimposed upon the tractor the combined unit becomes an articulated vehicle, which we do not want, as I shall show a little later.
In the case of a tractor-trailer combination the weight which is superimposed upon the tractor will be less than 1-10th of the total and that, I have been informed, is not regarded as "a substantial part." In those circumstances the tractor-trailer combination would not be classified as an articulated vehicle, but instead would rank as a load-carrying vehicle (either a light or heavy motorcar) drawing a trailer. That point is important, because it allows the overall length to loc 34 ft. and affords a trailer length exclusive of drawbar Of 22 ft.
Reference must also be made here to the Finance Act, under which taxation is imposed. The tax on a tractor and trailer, regarded as I have just defined it, would be much less than would be the ease were it considered as an articulated vehicle. Now, the Finance Act describes an articulated vehicle as a towing vehicle which is attached to it's trailer by partial superimposition. I believe the word "is" in the above definition is to be interpreted as meaning always" and the word "attached ' as "coupled." In the ordinary way a tractor and trailer are not attached by this method but are merely coupled up without any superimposed weight. Provision is made to superimpose some weight if' it be desired, but that is not the same thing.
tsers of tractor-trailers should study the foregoing• extremely carefully and bear it in mind when
registering their vehicles. It is distitictly to their advantage to keep the vehicle in the one clasSificatiOn for licensing, speed limits and constructional regulations, and they will serVe their " own ends best if they run them as loadcarrying vehicles drawing trailers.
In that way they will reap' the benefits of reduced taxation and increased Iiinits of overall dimensions. It compels them, however, to bear in mind the need for provision, in the coupling between tractor and trailer, for superimposing some of the load of the latter upon the former and makes it necessary for them to fit pneumatic tyres.
What does emerge from the foregoing is this: if there be an arrangement whereby the drawbar between the tractor and trailer can be manipulated so as to transfer a small portion of the weight, in the manner described, from trailer to tractor, then a pneuniatic-tyred outfit may travel at 16 m.p.h: Its gross weight may be 22 tons, and as the tractor and trailer can be brought well below a limit of I tons in weight it is possible for the pay-load to he 15 tons. So much for the legal aspect of the matter ; in the next article I propose to deal with the economics of the use of this type of machine.