Brake fade tests and cut-in limits coming?
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• Because heavy vehicles are now being driven faster. the Ministry of Transport is seriously considering the specification of a brake fade test at the manufacturing stage: it is also thinking of making regulations which would specify the maximum permitted cut-in of rigid and articulated vehicles on curves.
This was revealed by Mr. Dennis Baker, senior engineer, Ministry of Transport, in London last week when he presented a paper on future legislation at a commercial vehicle conference organized by Henlys Ltd. and Stewart and Ardern Ltd. to coincide with the announcement of the BMC Boxer range (CM last week).
His fellow speaker was Mr. Donald Goodier, product planning manager of British Leyland Truck and Bus Division. The success of the meeting was aided by the lively participation of the transport operators present—livelier perhaps than the organizers anticipated.
Other important points to emerge from Mr. Baker's paper were:
• Compulsory fitting of anti-jack-knife devices is a "distinct possibility".
• The present length limit of 15 metres is unlikely to be increased.
• A simple power-to-weight ratio is more likely than gradient or speed performance formulae.
• Heavier vehicles will not be accompanied by a rise in the 10-ton axle limit.
• Axle spacings may be reduced to give, for example, more compact 32tonners.
• Load height may be limited to 13ft in the interests of stability.
• New rules on load securing may be introduced.
Mr. Baker emphasized that the Ministry was not committed to raising maximum vehicle weight limits and was at present only exploring the possibilities with the manufacturers and the operator associations: it was only when— or if—the scope for increases was accepted that proposals would be circulated for comment and then submitted to the Minister for a decision.
There were two main reasons, said Mr. Baker, why an increase in maximum axle weights was unlikely: it would probably cause considerable increase in road-surface repair costs because of damage to the foundations, and there were many sub-standard bridges in the country. A recently completed two-year exercise to assess bridge strengths on the basis of a 10-ton axle limit showed that many were unable to take a 10-ton loading and had had to be down-rated. This was why there had been a sudden increase in the number of bridge restrictions, forcing heavier vehicles to follow alternative routes which sometimes involved considerable diversions.
Even on the Continent, he said, there was no strong move towards greater axle weights. The 13-ton axle was permitted in France. Belgium, Luxembourg and the Saarland district of Germany but elsewhere 10 tons was the rule. Italy had considered a 13-ton limit but had now decided on 10 tons and even in France there were indications that the 13-ton limit might prove too heavy when road and bridge repair costs were assessed. If France downrated, Belgium and Luxembourg were likely to follow and in any case 13-ton axles were heavily taxed in France.
Axle-spacing problems
But in Britain, said Mr. Baker, there seemed to be scope for an uplift in maximum weights linked with control over axle spacings. The Ministry would prefer the limits to be applied over intermediateas well as outer-axle spacings, which would permit maximum benefit to be obtained from any scope-for-weight increases, but the manufacturers felt that this would provide too many design complications, Added Mr. Baker: "It rather looks as if any possible increase will be linked to outer-axle spacings only, but these will have to be greater than they otherwise would have been in order to cater for the absence of control over the spacing of intermediate axles." There was a strong possibility that the present spacings might be reduced, and the 32-ton four-axle artic, now required to have an axle spread of 38ft, might benefit in particular.
No increase in the maximum lengths of 11m 136ft 1in.1 for rigids, 15m I49ft 24-in.) for artics and 18m (59ft approx) for drawbar combinations was likely, said the speaker. Whatever maximum weights were chosen, there would still be difficulty in carrying a maximum-weight 40ft container, and especially two 20ft units; the fully loaded 40ft type was unlikely to be used to any great extent because it could not be hauled over the road on the Continent or in most US States. But because of the greater outeraxle spread, more weight could theoretically be allowed on a drawbar combination and there might be more scope for this type in the future.
Power-to-weight likely
Among associated legislation which might be introduced to coincide with any weight increase was a minimum power-to-weight ratio. The Ministry was considering what basis should be chosen for minimum power requirements and there were good reasons why vehicle performance should be specified not on a simple ratio basis but on the speed which must be maintained up a given gradient, or the time required to accelerate from rest to, say, 20mph. But such a specification would involve some form of type approval and would probably be impracticable to enforce on vehicles in use. So in spite of its disadvantages, a powerto-weight criterion was the most likely basis for legislation.
Brake fade was likely to become a prominent problem if weights were increased, said Mr. Baker, and the higher braking efficiencies now specified had been matched to a certain extent by the higher speeds of heavy vehicles. The Ministry was therefore considering specifying a brake fade test at the manufacturing stage. Brake lining characteristics had a considerable influence over fade-resistance properties, and the problem would be how to prevent alternative but less suitable linings being fitted on vehicles in service.
Jack-knife requirements
The problem of jack-knifing had still not been resolved. Mr. Baker claimed. While operational service trials were not yet complete, interim results proved the desirability of providing devices to prevent driving-axle and trailer-axle locking under light loads and heavy braking and driving-axle locking on rigids. It was too early to say whether such devices would become compulsory but it certainly remained a distinct possibility.
Mr. Baker revealed that civil engineers in the Ministry had long thought that there should be some relationship between the swept paths of heavy vehicles and the specifications which they laid down for road junctions and roundabouts. There was little point in laying down a design for a junction, only to find that there was nothing to prevent the use of vehicles which were unable to manoeuvre in the space provided. This situation could be remedied by including in regulations a specification for a swept path which all vehicles would have to be able to negotiate without infringing the inner and outer boundaries.
This specification would not be unduly severe and was likely to be based on the swept path of a 32-ton four-axle artic with a 38ft outer-axle spread when turning inside the outer turning circle of a 28-ton four-axle rigid vehicle having a 26ft outer-axle spread. These were vehicles which had the minimum axle spacing required by the present regulations for maximum-weight four-axle rigids and four-axle artics.
Stability tests?
There had been a number of spectacular accidents recently in which articulated vehicles, particularly tankers, had overturned, said the speaker. There was little doubt that an improvement in roll stability would make this type of accident less common, but therewas no control over the stability of any goods vehicles except spirit tankers and even in this case the control was rather empirical and took no account of the roll stiffness of the suspension.
Two possibilities existed for enforcement of any regulatory requirements on roll stability. It could be laid down that vehicles should be able to negotiate a curve of specified radius at a specified speed without the inner wheels lifting off the ground. Alternatively, a minimum angle of tilt without overturning could be specified. The Ministry was considering both these possibilities, but investigations so far had been confined to tankers.
A test for platform vehicles would be more difficult to specify because of the great variety of loads carried and the lack of control over the height of the centre of gravity. But it was felt that an overall limitation of loading height would be beneficial, and a figure of 4m (13ft) had been suggested as a maximum.
Possibly because of a lack of suitable vehicles, said Mr. Baker, it had become common to see containers being carried on platform vehicles with very little regard to the proper securing of the container; in many cases rope was used but sometimes there was no securing at all.
The police were becoming particularly perturbed about this situation, especially because of accidents occurring through containers falling from vehicles. The police were also finding it difficult to prove cases of insecure loads under regulation 76 of the C. and U. Regulations. Mr. Baker said it might therefore be necessary to strengthen this regulation to cover the carriage of containers and specifically require that they be restrained by properly designed twist locks or by having steel rings which could be used in conjunction with a chain and turnbuckle.
Asked by an operator whether he would agree that the Ministry was wrong in making vehicles fit the roads, rather than making roads to fit the vehicles, Mr. Baker said that roads came first and one could not expect to remedy the existing road and bridge situation overnight. It was only reasonable that a bridge engineer should expect vehicle design to be modified to suit, and raising axle weights above 10 tons would increase road repair costs astronomically.
Mr. Baker was asked whether chains were really an adequate substitute for twist locks in fastening containers, and answered: "Yes— but we are really concerned about the use of ropes.'" A question on policy concerning towing regulations met with the reply that there was no train weight allocated to rigids towing drawbar trailers, but it might come in the future.
' One operator wanted to know why MoT offices worked only a five-day week, and not for seven days. Mr. Baker said that Saturday opening had been considered but there were not sufficient staff available.
Pressing for 13-ton axle
Mr. Goodier explained to the audience how British Leyland studied the needs of the market and their customers. He spoke of the need. which had now been met, for a new range at the Boxer's weight and illustrated the design features of the new model and its particular advantages.
Saying that the Ministry must not introduce punitive legislation, and that manufacturers needed to make vehicles that could be supplied to world markets, Mr. Goodier revealed that his company was pressing for the introduction of a 13-ton axle limit. He, too, thought that there could be interesting developments in the drawbar trailer field but he suggested that, because haulage of 40ft containers was a major problem, a relaxation in maximum length to permit 15.25m or 15.5m would be a considerable help.
The first question faced by Mr. Goodier was: "When is British Leyland's sales drive going to be backed by after-sales service—this is a real headache?" The questioner explained that of 67 JU250 vans (part of an order for 2901 delivered in the past nine weeks, 24 had broken down between the suppliers and his branches, all with water-pump failure.
Mr. Goodier explained that this was not really within his province, since JU250 vans were not made by the Truck and Bus division. The questioner retorted that he had sent photostat copies of all the correspondence concerning this matter to the managing director of B MC some time ago but had received no reply.
Mr. Goodier suggested that this was perhaps because BMC no longer existed as a separate company.