Q My firm operates a mixed fleet of
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articulated vehicles with air brakes. Tractors are either plated three-fine braked models or older maximum capacity two-line, but the trailers range from unplated singleaxle (air), up to plated tandem axle with three lines, some of which are built to operate at the maximum weight of 32 tons gross.
Can three-line units legally be used with two-line trailers and vice-versa? If so, what gross vehicle weights will apply?
AThis problem is a common one and there is no doubt that in many instances outfits have operated outside the legal gross because of pure ignorance. In "mixed" operations it is necessary to restrict outfit weight to the maximum operating weight that is applicable to the unplated unit, be it tractor or trailer. Hence a 30-ton-gross tractor when operating with an unplated two-line "maxtrailer is allowed 24 tons gross combination weight only.
Similarly a plated three-line tandem-axle or three-axle trailer can only be loaded to 24 tons gross when used behind an unplated two-line tractor. Single-axle two-line unplated trailers can only operate at 20 tons gross, and should not be confused with the singleaxle three-line plated model which when coupled to a matched tractor can operate at 24 tons gross train weight, provided the outer axle spacing is at least 18ft, and there are two independent braking systems giving 50 per cent and 25 per cent efficiency respectively.
One must take into account the introduction of vehicle testing and plating. as with older equipment the plated weight may be below that for which the vehicle was originally designed. For instance the 24-ton-gross limit will no longer have application to eightwheeled outfits by virtue of the Construction and Use Regulations alone,