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IN view of the growing popularity of articulated vehicles for all classes of haulage work, it is strange that so few of them are manufactured as complete vehicles. At present, an operator wishing to buy an articulated outfit is entirely free to use any type or make of tractor with any type or make of semi-trailer, assuming, of course, that suitably matched coupling gears are fitted. Only one concern in this country makes complete articulated outfits, although matched 24-tongross vehicles are being built to the special order of British Road Services, who have obviously appreciated the shortcomings of indiscriminately mixing tractors and semi-trailers of different characteristics.
The articulated outfit, properly handled, can be as safe as a rigid vehicle, but in emergencies the braking system can make or mar its stability. To be fully efficient, the timing of the braking circuit is highly important: so, too, is the correct braking ratio between the three or four axles.
A perfect braking system for articulated vehicles can be evolved only when the separate systems of the tractor and the• semi-trailer are correctly matched by experimental use of the complete vehicle. There are no standards to which individual tractor and semi-trailer rnanufacturers can work when designing the braking systems on their own units, with the result that it would be rare to find any two makes of tractor or semi-trailer with identical braking characteristics.
With the increasing use of interchangeable coupling gears, " mixing " of different makes of tractor and semitrailer within fleets is common. Every time a tractor is coupled to a different semi-trailer the braking characteristics of the complete vehicle are, consequently, changed.
The solution, of course, would be for definite braking standards to be laid down, to which all tractor and semi-trailer manufacturers would adhere strictly. Axle loadings and the longitudinal location of the coupling pivot relative to the rear-axle centre line would also be taken into account.
It is surprising that more vehicle manufacturers have not taken up the production of semi-trailers, which would then enable them to offer complete, proved. matched outfits. Admittedly, there would be nothing to stop an operator using the tractor or semi-trailer from one of these matched outfits with a semi-trailer or tractor of another make, but at least a start would have been made.
Haulage to and from the Continent is causing another difficulty with articulated outfits. Some Continental operators are having to order tractors specially equipped with coupling gears which will handle British semitrailers. Although standard types of turntable and king-pin will often be encountered, there are sometimes wide differences in turntable heights and semi-trailer front overhang. That is why specialized vehicles have to be employed for what should be a simple exchange of tractors.