Some existing vehicles will have trouble meeting brake
Page 33
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standards BY THE MECHNICAL EDITOR THE interim braking standards for existing vehicles which were published last week had been eagerly awaited for some time, and the proposed braking efficiencies for the classes of vehicles covered are more or less as expected. There is an extra point, however, in the section of the draft proposals dealing with attics which are a combination of new and "old" units—a new tractive unit with an old semi-trailer and vice versa. ("Old", in this context is pre-1967 unplated.) As the draft regulation is worded, it appears that this sort of mixed outfit will have to meet the 50 per cent and 25 per cent for main and secondary systems as required of a wholly new outfit. But, on checking with the Ministry, it appears that this is not the intention and that "mixed marriages" will require only the lower efficiencies specified for old outfits. This creates no novel situation as they cannot then take advantage of the increased weights permitted under the latest regulations.
It is quite obvious that the brake efficiencies that will be required (45 and 20 per cent for the service and secondary brakes respectively on two-axle rigids, and 40 and 15 per cent for multi-wheelers and artics) will cause much scratching of heads in many fleets, particularly where fairly old vehicles are operated.
The requirements for secondary brake efficiency—which in most cases will refer to the handbrake—will be the harder to meet without some modification in the way of adding power assistance. The figures that are going to be required for the main service brakes are not so severe but, even so, they will be difficult to obtain on many vehicles —and even where attainable after adjustment, 40 per cent will be difficult to maintain on some artics at all times between services.
Because no reference is made to delay in application of the actual brake units, the draft regulations do not make a major contribution to improved safety. Certainly they will go a good way towards ensuring that all vehicles do have some braking but just because two vehicles give the same reading on a brake meter it does not mean to say that they can stop in the same distance. If in one case there is 1 sec. more delay between applying the pedal and having the brakes on, then it is going to require 44 ft. more to stop from 30 m.p.h.
In the letter from the Ministry of Transport accompanying the draft regulations one sentence includes the words "the method used to calculate efficiency relates the force exerted to stop the vehicle to the weight of the vehicle". It is from this that the use of brake meters to check vehicles can be assumed; and it can also be presumed that peak readings will be used, so if a vehicle gives the required figures at any time during the test-stop it will pass. It is obvious that the only way quick tests can be carried out is by the use of brake meters and for this reason some of the disadvantages this entails must be accepted.
But it must not be imagined that when the regulations come into force we shall suddenly start getting much safer vehicles. Safety will be improved, but some vehicles will still have much better brakes than others and the main responsibility for preventing accidents will continue to lie with the driver's ability to use his vehicle according to its capabilities.
(Achieving better braking by systematic maintenance is discussed on pages 72-74)
RHA Warning
THE latest brake standards were discussed on
Tuesday by the RHA highways and vehicles committee. It was agreed to advise members buying new vehicles to seek assurances from suppliers that braking systems were up to the standards which are to be laid down, or could be adapted to comply with them.
Members are urged to take particular care when buying vehicles specified with vacuum brakes, and the committee recommends airpressure brakes when buying artics.
Temporary Closure of A5 Section
THE Ministry of Transport has announced that a length of Brockley Hill (AS) from its junction with Edgware Way (A41) southwards for a distance of 210 yards will be closed for about six weeks from Sunday (April 24).
This is to facilitate the completion of MI extension from Berrygrove, which is due to be opened to traffic in September, and the Hendon urban motorway. The Ministry will later announce details of diversionary routes and other traffic arrangements.