What the New Proposals Mean
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BY THE TECHNICAL EDITOR BRIEF details were given in last week's issue of the proposals for increased sizes and weights of commercial vehicles. The Ministry of Transport has followed its preliminary announcement with more complete details of the proposed changes, comments on which are invited to be made not later than March 31.
It is quite obvious that the proposed changes have been formulated with the object of bringing Great Britain more into line with the rest of Europe, but because of present road conditions in this country and, in particular, of the strength of bridges the suggested new regulations contain a number of conditions which tend to make the proposed figures more complicated than those at present in effect. As the Ministry says in its letter containing the new details: " It is not suggested that vehicles up to the larger dimensions and heavier weights set out in these proposals are suitable for travel on all roads without distinction: but neither are vehicles built and loaded up to the full existing maxima. The question is whether they are generally within the capacity of the main road system in this country today ".
The letter states also that further consideration will be given in due course to this country's position in the light of whatever international agreement may eventually be reached on maximum weights and dimensions for vehicles engaged in international traffic. Nevertheless, the Ministry considers that the present regulations need fairly immediate revision in order to increase the productivity of the road transport industry in the home market and its competitiveness in the international market, and to facilitate the exports of commercial vehicles.
Taking the dimensional sections of the • proposals first, the new width of 8 ft. 2-5 in. for all vehicles, irrespective of weight (except for locomotives, which
• stay at 9 ft.), is an obvious move, as it was quite ridiculous for p.s.v.s to be allowed this figure while goods vehicles were not. Obviously not all hauliers will want vehiclesbuilt up to the full proposed width, but the extra 2-5 in. could be made good use of by vehicle designers in that it would permit them to use wider brakes or springs and, it is to be hoped, encourage them to design cabs of a more reasonable width. Additionally, the extra 2-5 in. could be made use of by bodybuilders—particularly tank manufacturers
B30 —to reduce overall body height slightly without loss of volume, and therefore provide greater vehicle stability because of a lower centre of gravity.
In the same light, the proposed maximum length of 36 ft. for all rigid vehicles is a logical follow-up from the increase of the limit for p.s.v.s which took effect in 1961. However, as will be discussed later, it is intended that full use be made of the extra 6 ft. allowed if proposed increases in maximum weight are to be taken advantage of, this obviously being for the purposes of reducing unit loadings on weak bridges. No recommendations are made to define turning circle for rigid vehicles at the new length, and manufacturers will obviously have to take the law into their own hands in this respect, for otherwise vehicles built to the full proposed length would obviously be too unwieldy for use in congested conditions if turning circles were allowed to rise much above the currently accepted standards.
The proposed length of 42 ft. for articulated vehicles (other than those designed to carry long indivisible loads, for which there is still to be no set limit) is less than figures currently permitted on the Continent, most countries allowing 46 ft., whilst Germany allows 49-2 ft. The proposed British limit is sensible, however, in that articulated vehicles of over 45 ft. length can become difficult to handle under congested street conditions. Being 7 ft. more than the present maximum for artics, the proposals mean that payload space could be increased by a corresponding amount, whilst the weight proposals permit greater tonnages to be carried when advantage is taken of the maximum permissible length.
Apparently, maximum lengths for lorryand-trailer combinations are to remain loosely defined, the proposed dimension for a vehicle with one trailer being "about 63 ft.", whilst a vehicle with two trailers will be allowed to run at "about 90 ft. ". Obviously the ruling here is an increase in overall length of 6 ft. above the present figure, which 6 ft. could be either on the towing vehicle or on the trailer or split between the two.
The more significant changes lie among the proposed weight limits, and these will entail considerably more complication in interpretation of the law than those currently in force. Virtually the only limit unchanged is that for a "single four-wheeled axle "—in other words, twin oscillating axles—the figure for which remains at 11 tons. This will, of course, remove a lot of the advantage that this wheel formation has at present, as under the proposed regulations a single axle fitted with twin tyres (" at not less than 12 in. centres ") will have its limit increased to 10 tons, although the figure for a single axle with single wheel remains at 9 tons. Furthermore, the gross-train-weight limit for articulated vehicles with twin-oscillating-axle semitrailers remains at 24 tons, although the raising of the driving-axle limit to 10 tons will make it easier for operators to load their semi-trailers without exceeding statutory axle limits, the proposals making it necessary to put only three tons on the front axle if running at 24 tons, whereas at present it is necessary to try to get four tons on the front wheels.
At present, the rulings for a tandemaxle bogie are that the total load to be carried by the bogie is double that of a single axle, in other words 18 tons. There is no distinction for bogies of varying axle-centre dimensions, whereas on the Continent some countries have as many as three different bogie-loading limits according to the length of the bogie. It is proposed that this shall be changed in future: the 18-ton limit is to remain, provided the bogie-centre dimension is between 4 ft. and 7 ft., but if the dimension is less than 4 ft. a new limit of 16 tons is proposed, though this should not affect self-propelled heavy goods chassis, which invariably have bogie-centres of more than' 4 ft.: some tandem-axle semitrailers get very close to the limit, however. The proposed regulations do not state that the axles of a bogie must be equally loaded, therefore presumably it would be permissible for a single-drive bogie to have a driving-axle loading of 10 tons.
At first glance it would appear that the current gross-solo and gross-train-weight limits are to remain unaltered, but then one comes to the footnotes, which present a very different picture. For example, a rigid two-axle chassis is limited to 14 tons gross, as at present, unless the axles are more than 12 ft. apart, in which case the limit is raised to 16 tons—a figure widely favoured in Continental countries also. For a vehicle to run at this new weight it is obvious that it will have to have a 10ton axle at the rear and a 6-ton unit at the front, and whilst there are some manufacturers currently fitting axles of these capacities, there are quite a few who will have to either make or purchase
new types if they are going to build for the new limit.
As with the four-wheeler, so with threeand four-axle chassis: provided the outer axles of a three-axle machine are more than 18 ft. apart its proposed grossweight figure is 22 tons—the figure being 20 tons otherwise, whilst an eight-wheeler will be permitted a gross weight of 28 tons if the outer axles are more than 26 ft. apart. The wording used here is that employed by the Ministry, but presumably " apart " can be taken to mean the distance between axle centres. It can now be seen why it will be necessary to take advantage of the proposed 36-ft. length limit if it is desired to run an eight-wheeler at 28 tons gross, because at present an average 30-ft.-long eightwheeled chassis has a dimension of under 20 ft. between the centres of the first and fourth axles.
Thus the 28-ton-gross eight-wheeler of the future will have to have a wheelbase of at least 23 ft., which helps to explain my earlier remark about manufacturers having to use their own judgment as to turning circles: a 23-ft.-wheelbase eightwheeler with the same front-axle locks as at present would have an enormous turning circle—at least 90 ft.—and the position would be aggravated by the need to have larger front tyres than at present, as the front-bogie loading would have to be at least 10 tons if the proposed 18-ton bogie limit is observed at the rear!
In order to get the required front-axle lock, it might even be necessary to adopt a horizontal engine layout, with the engine mid-wheelbase, thereby permitting the chassis frame in the immediate vicinity of the front bogie to be narrowed so as to give the required tyre clearance without having to allow room for a power unit there.
It is interesting to note that Britain steps out of line with current Continental practice in proposing separate weight limits for four-axle chassis, as every Continental country at present lumps threeand four-axle machines in the same category. Perhaps this is something British hauliers can be thankful for, as otherwise they might be faced with the 22-ton limit which it is proposed should apply to six-wheelers.
The "articulated vehicles" category is extended under the new proposals to differentiate between outfits with four and five axles: under the present regulations both these types are limited to 24 tons. The limit for a three-axle artic. remains at 20 tons unless the outer axles are more than 18 ft. apart (the same dimension as for a rigid six-wheeler), in which case the outfit can run at 22 tons gross, or 24 tons—as at present—if the semi-trailer has twin oscillating axles. There are three limits for four-axle outfits: the present limit of 24 tons will continue to apply if the outer axles are less than 26 ft. apart (again, this is the same ruling as for a short rigid eight-wheeler); when the outer axles are more than 26 ft. apart but less than 35 ft. apart the " rigid " limit of 28 tons applies, whilst if the 35-ft. dimension is exceeded the figure becomes 30 tons. There is yet another proviso; 32 tons is permitted if the dimension is more than 40 ft., but. this, of course, applies only for long indivisible loads.
The complete newcomer to the British field is the five-axle artic. . As with the four-axle type, the limit for the 10wheeled combination is 24 tons if the outer axles are less than 26 ft. apart, or 28 tons if the distance is between 26 ft. and 35 ft. Above 35 ft., however, a 32-ton limit is proposed. It will be interesting to see how hauliers try to take advantage of this 32-ton limit. It is highly probable that some will use thirdaxle conversions to apply to four-wheeled tractive units for use in 'conjunction with semi-trailers of 30 ft. ' or thereabouts length. Assuming that it is possible to load the semi-trailer bogie up to 18 tons, it then becomes necessary to ensure that the remaining 14 tons is distributed over the three axles of the tractive unit, and to do this longer chassis wheelbases will probably have to be adopted.
No changes are proposed for the maximum gross train weight of a lorry and trailer, it being intended that the current figure of 32 tons should apply, with the proviso that the limit is 24 tons if power brakes are not fitted or 40 tons for trailers drawn by locomotives. Similarly, the current rulings for locomotives are not affected by the latest proposals.
Welcome as these changes will be in certain sections of the industry, there will obviously be many operators who will either be unable or without wish to take advantage of the increased weight and dimension limits. The proposed changes are, however, all to the good, though as they stand it must be admitted that they cannot be said to offer hope of reducing road congestion.
To my mind one very important thing has been omitted, this being a minimum power-to-weight ratio. As the proposals stand, there is nothing to stop the inconsiderate operator buying a 7-ton four
wheeled chassis, equipping it with a third-axle conversion and a coupling gear, and running it in conjunction with a tandem-axle semi-trailer at a gross weight of 32 tons. Such a vehicle could have an engine developing a mere 90 b.h.p., but even assuming it had a 100-b.h.p. unit the power-to-weight ratio would then be 3.125 b.h.p. per ton, which is completely ludicrous. In my opinion, no vehicle of this weight should have less than 200 b.h.p. Admittedly, proposals are in the wind for the enforcement of plating, with which will be tied-in an unspecified engine requirement, but plating has been on the books for many years, and still seems to get no nearer.
The question of braking ought to be taken into account also, particularly if— as at present—no speed limits are to be enforced on motorways, though the position could get serious enough with the 40-m.p.h. limit which becomes effective tomorrow. Conscientious manufacturers will, undoubtedly, fit larger and more powerful brakes to any vehicles built to comply with the proposed regulations, and at least three British manufacturers are already able to offer .200-b.h.p. engines of their own make, but the chassis makers who have to rely on proprietary units are not in such a happy position unless they are prepared to add to the weight and costs of their products beyond reasonably acceptable limits.
What this boils down to is that vehicles designed for operation at these larger dimensions and higher weights will be noticeably heavier than current designs intended for use at 24 tons, therefore not all the extra 4, 6 or 8 tons which the proposals define will be available for payload. Chassis-weight increases of at least 1 ton must be expected, whilst the figure will be around the 2-ton mark when comparing a 42-ft.-long, 32-ton-gross fiveaxle artic. with a present-day 35-ft.-long, 24-ton-gross four-axle combination.