Q I am puzzled by one of the diagrams
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in the guide to weights and dimensions published in COMMERCIAL MOTOR on July 7. This is the vehicle-trailer combination which is shown as having a maximum permitted overall length of 59ft 0.75in, yet the sum of the individual lengths of vehicle (36ft I in) and trailer (22ft 11.5in) plus allowance for a drawbar comes out at more than this. Surely this is wrong? The sum of vehicle and trailer totals 59ft 0,5in, leaving 0.25in for a drawbar!
AThe puzzlement is understandable, but
the figures are correct. The very fact that there is a separate limit for the overall train length is an indication that the Ministry does not intend maximum-length components to be coupled in the same outfit, otherwise there would, as you say, have to be an overall allowance of about 65f1—including about 5ft for a drawbar.
The situation which the diagram is intended to convey is that there are three limits on permitted length in a rigid/drawbar combination: the towing vehicle may not exceed 36ft lin, the drawbar trailer may not exceed 22ft 11.5in, and the whole train may not exceed 59ft 0.75in. These figures refer, of course, to operations under Construction and Use provisions. The practical effect of this is that if one uses a maximum-length towing vehicle, then the trailer will have to be sufficiently shorter (say 18ft) for the whole outfit not to exceed the train length limit. The reverse is true.
Recent proposals from the Ministry will, if approved.permit longer drawbar trailers to
be used, but there is no present intention to increase the permitted combination length. Incidentally—a point raised by several inquirers—the reason why these maximum lengths are such odd figures, with fractions of an inch in several cases, is that Continental metric limits have been generally adopted as a move towards international uniformity, and these convert into odd British sizes. (For example, 59ft 0.75in is 18 metres).