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17th December 1971
Page 45
Page 45, 17th December 1971 — topic
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Which of the following most accurately describes the problem?

Keywords : Truck, Axle

Easyon the bridges

BRIDGES seem to be currently very much a matter of concern. There are qualms about the dependability of box girder bridges on motorways; a lorry load of timber has wrecked a much-loved bridge in the BBC's mythical village of Ambridge; there is a revival of interest in a bridge across the Channel; and, depending on the point of view, bridges are the heroes or villains of the latest decision on maximum lorry weights.

Exactly one year ago, the Minister for Transport Industries, Mr John Peyton, announced that there was to be no increase in those weights. His statement marked the culmination of a swelling campaign against proposals from manufacturers and operators that the maximum should go up from 32 tons to at least 36 tons or 38 tons.

In the earlier stage of the discussions, it became clear that the limiting factor in the eyes of the Government was the load capability of bridges. Expert opinion fixed on 44 tons as the maximum vehicle weight which bridges in general could sustain.

In course of time, 44 became for many interests the figure of the beast. The forces of reaction seized upon it as a target for their abuse. As it happened, the Ministry of Transport, with which the earlier negotiations had taken place, was translated into a sector of the new Department of the Environment, where everything looked different.

The bridges had not changed. A higher gross vehicle weight was no more likely than before to endanger them; nor was there any proof that it would have the other deleterious effects that were feared. It was enough that the fear was expressed from a number of interests claiming to speak on behalf of the environment. A Minister dedicated to that somewhat nebulous abstraction had to take notice of the critics, and the hope of any advance on 32 tons vanished through the discreet medium of a written answer to a Parliamentary question.

Research on the bridges has continued. Recently, according to the Department, "more precise calculations of bridge stresses" have been carried out. They apparently justify the reductions now being offered in the minimum axle spacings for given laden weights.

It is even possible, although the official announcement makes no mention of the matter, that they can take the credit for the increase in the top limit from 22 tons to 24 tons for rigid six-wheelers and from 28 tons to 30 tons for rigid eight-wheelers. But 32 tons remains the limit for articulated vehicles.

This prudent retention of the final barrier in the proposals may explain the lack of positive reaction from the environmental interests. Alternatively, they may have found it difficult to understand what the proposals mean. There was a time when it was considered sufficient to place a single limit on each main vehicle category: the four-wheeler, the six-wheeler and so on.

In some quarters the present complicated provisions were thought to be provisional even before they came into effect in 1964. Most operators regarded them as unsatisfactory, not so much for the restrictions on the maximum limits — which were substantially higher than previously — as for the awkward axle spacings, which among other things often made it necessary to have longer vehicles than would otherwise be necessary.

The hope was for a return to simplicity, no doubt coupled with further relaxations. The new proposals extinguish any such hope. Certainly, they will allow reduced axle spacing for many types of vehicle, but at the cost of much more complicated weight schedules.

The greater complexity, says the Department, is the price to be paid if maximum design freedom is to be given to manufacturers without endangering bridges. At every point it is the bridges which have to carry the blame as well as the vehicles.

Admittedly, care has to be taken to ensure that bridges are strong enough for the traffic they have to bear. It is still strange that they should have become so obsessive a theme, even to the point of provoking legislation which looks like a row of beads.

Other countries seem to make do with much less detailed provisions. They also must have bridges on their roads. The research which has made such precise calculations possible in Britain must have involved a wide variety of bridges of every size, shape and material. It would be curious if they were all found to have exactly the same breaking point.

Where there is a risk, a weight limit could always be applied to a particular bridge. The road transport industry may also wonder to what extent work is on hand for strengthening the structures. Such an activity should be an integral part of the augmented road programme for which the Minister deserves to be congratulated.

The true symbol of the bridge may be that it links him with the opposing interests and still keeps them apart. It gives him a practical reason for restraining the demands of the industry for heavier vehicles — a demand which Common Market membership will redouble — and for silencing the clamour of the environmental lobby without appearing to give in to it.

by Janus

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