• MOTOR VEHICLES AND THE ROADS.
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Three Points of View on the Relation of Vehicle Construction and Road Maintenance.
THE FIRST of the three important papers on this subject gave the petrol makers' standpoint. It was read by -Mr. W. D.
Williamson, Who
its hitroduettion, the self-piopelled vehicle as as allowedUpon the road on sufferance only and thishas been the position ever since. The road engineers have been inclined to look upon vehicle manufacturers as taking .a fiendish delight in the destruction Of roads, forgetting that, if a vehicle is destroying the road, it is certain that the road must simultaneously be destroying the vehicle. -Every vehicle depreciates more rapidly on bad roads.
From the national standpoint, the preservation ef vehicles is just as 'important as the preservation of roads. It is just as necessary to apply regulations governing the strength and nature of roads as regulations controlling the weight and speed of vehicles. The latter should be based on the sole consideration of efficiency and economy of transport and not merely on the consideration of road wear. While the motor vehicle user may still have to live in peril of the police trap or.the weighbridge, the, road maker might well be faced with the use of some instrument which, taken over a strip' of road at a given speed, would register the undulations and coixlemn any length of road not complying with legal requirements.
• No motor manufacturer would suggest driving a vehicle over any road that would abnormally reduce the vehicle's life. Given suitable roads, however, the speed of 'heavy lorries could he very materially increased. The user. of the lorry naturally wishes to make the most of its possibilities. The manufacturer is interested, -because anything Which increases the efficiency of the vehicle also increases the uses to Which it can be applied and, therefore, the demand for it.
' The serVice capacity of the lorries in this country is reduced by 25 to 50 per cent., due to restricted speed limits. If 'roads generally were equal to our best roads this reduction of efficiency could he eliminated, reasonably increased speed limits being permitted. We should, thus, get more service from a gh en number of vehicles with a corresponding reduction in the congestion of traffic. Speaking generally, the report of the Local Government Beard Committee, 1918, absolved the rubber-tyred vehicle from blame for undue damage to roads provided that the latter are properly constructed and maintained. The sole exception was in respect of watef-bound macadam roads. Even from strict considerations of road damage it does not appear necessary to limit the axle weight of a trailer to half that of the power vehiole. Control of axle 'weight and gross weight should, in all cases, be sufficient without legal limitations of unladen. weight.
The Influence of Road Surface Variations.
The developmentof vehicles in various countries is influenced by national characteristics and the national system of roads. The .solid reliability of British design is characteristic of all our engineering 'work. British roads, being seldom straight, do not tend to produce vehicles that can be used at very high speech. Our road surfaces are such as 1 o cause great attention to be given to springing. The road with broken of uneven surface is the road which in this country has the .greatest influence on design. In a trip of 20 miles one may encounter good setts, bad
setts, good tar macadam, wood paving and rough macadam.
The chassis designeris faced with the problem of producing a vehicle to give good results on any of these surfaces. Given roads with really good surfaces everywhere, road vehicles would be produced which would impose much legs total
weight in proportion to -the useful loads carried. These lighter Vehicles wetild have less ill-effect upon the roads and would; therefore, reduce road •upkeep s This 'means :additional strength and additional weight:' Wheels must be robust to withstand shocks, axles must be unduly strong and heavy. • If roads were 'better, steering gear could be lighter and the springing stem ; whits lower in weight, could -be substantially: improved. Frames also could be. lightened, and the sanie•Afkiment applies to almost the whole Of the. thechanism.
Better roads mean also lower, running _mists Of vehicles. The ma.nufadturer of a vehicle ; when thinking in terms of operating costs; 'must take tyre wear into account, and tyre wear means road wear. It is caused largely by wheel spiii 'on rough road surfaces. The wheel rises after striking an obstacle and, when it hits the ground, the tyre is travelling at a speed too high for the speed of the lorry. • This is a great cause of tyre abrasion, and must equally cause road wear.
• Good Roads Reduce Running Costs.
Detailed analysis of working costs leads to the following comparative results. If we take a Vehicle with a useful load of four tons, working under present laws and conditions and covering -300 miles a . week for 50 weeks in the year, the cost per mile may . be estimated at 14.64d. The cost per ton-mile of useful load is then' 3.66d. If roads were uniformly good. the useful load could be increased at least half a ton for the Same gross weight of vehicle. The speed could safely be increased to 16 miles an hour. The annual mileage would be increased and the bills for tyres and repairs per mile .would be decreased. Total cost per mile would work out at 11.4 pence, and cost per tonmile of useful-load at 2.53 pence. This shows a saving of over 30. per cent, on our total haulage costs, a result well worth serious consideration. An increase in the permitted axle weight in, conjunction with suitable • roads would reduce the cost of transport enormously. Road development-is not merely a matter of road -surface. Sharp curves and right-angled corners in .
.terfere with the freedom of the designer in wheel-. base and weight distribution, in some cases leading to extensive overhang. They also tend to produce rolling, which causes additional wear of tyres. • The grading of roads is a. very important matter, upon which the sizo of engine is largely dependent. Sudden changes of gradient, as On a humpy bridge, necessitating: high clearance amidshi of the vehicle may mean in turn an undesirable high centre of gravity: Considerations of grading and road surface play a very important part in the question of weight distribution in the vehicle.
The war has taught manufacturers a great deal, bad conditions exaggerating troubles which had hitherto been negligible. Some of these troubles were due to the dust formed on soft roads in dry weather which got into the cylinders and mechanism and caused ex • eessive wear. The same thing must be happening upon a lesser scale on our own roads. The demand for large wheels is mainly due to the poor conditions of many roads. The manufacturer desires only to provide the wheels which will give the best results. He is necessarily influenced by the user, who has to consider the height of loading platforms and the difficulty of loading from the ground if the vehiele floor is too Irigh.
Road engineers must be prepared for a large increase in the number of goods-carrying vehicles on the road and must provide roads that will carry the traffic of the future. The road of the future should be constructed entirely from considerations of its suitability for self-propelled vehicles. Animal-drawn traffic will die out and thin will simplify the problem. We need a series of wide through roads specially constructed for motor traffic-' with good foundations and waterproof surfaces. These should not pass through the centres of towns, but should be linked up by connecting roads. When any vehicle uses the roads in accordance with the legal regulations, there should be no possibility of a successful prosecution against the vehicle owner for extraordinary damage.
Steamers and goads.
The second paper, read by Mr. George Hoare, gave the steam vehicle maker's standpoint. He said :— The value and importance .of the work done by steam vehicles during the war cannot be too strongly emphasized. They rendered possible the transport of enormous quantities of munitions, building materials, etc., in dependable machines using native fuel. The manufacturers of these vehicles have long personal experience behind them and know very thoroughly the real needs of their various customers.
The steam tractors and wagons now in use -give general satisfaction, though the limit of weight imposed by law has restricted the designer, who has great difficulty in meeting the needs of the user and at the same time complying with the regulations. It has not been possible to include within the legal unladen weight all the equipment found necessary or desirable. The manufacturer does not see the practical value of restricting unladen weight, as, from the point of view of the roads1 the total moving weight of the loaded unit. is the all-important matter. If unladen weight is to be retained, the definition suggested by the Local Government Board Committee should be interpreted as excluding everything not essential to steaming on or off the weighbridge.
Some manufacturers would prefer unladen weight fixed at si tons. It has been found that unless the weight is sufficient to secure a firm grip of the road surface, there is a tendency for the driving wheels to skid, or slip even, if the load hauled is light. Any such action does much more damage to the roads than additional weight. The provision of wider spaces between the strakes on a metal tyre would generally prevent slipping. It is, therefore, suggested that, for wheels not less than 4 ft. 6 ins, in diameter, the space allowed should be one-fourth instead of one. eighth of the tyre width. This would not put heavier pressure on the road than is already recognized as reasonable.
There are many cases in which, it is desirable to permit supplies of fittings to be provided, not included within the legal unladen weight. For long-distance work in some districts, provision must be made for additional water and fuel supplies. For many classes Of work awnings to protect the engines are desirable. There are times when the provision of three-speed ratios is beneficial. The fitting of rubber tyres or pads should. be provided for but this, again, adds to weight. For acme wok special attachments such as hauling drums and ropes, interchangeable road roller parts and jib cranes are very useful, and should be allowed extra to the present legal unladen weight. Limitation of unladen weight in regard to trailers is entirely unnecessary. Surveyors themselves Ire c34
quentlY inquire for tipping trailers, which mean extra weight.
Turning to steam wagons, manufacturers would lite to see the rear axle weight raised from eight to nine tons' making the total Moving weight being then 13 instead of 12 tons. An allowance of a further half a ton should be made if rubber tyres are fitted. The definition of unladen weight already suggested for steam tractors should be adopted and the limit put at 6i tons. Where steel tyres are retained as being better suited to the work to be done, the use of crass-bars on the wheels must not be prohibited. The manufacturer on his side must endeavour to increase the efficiency of the springing arrangementsand, so, to reduce the wear and tear of the road.
The road surveyor's standpoint is indicated in a paper by Mr. Albert E. Brookes, who said:— The commercial and economic importance of the development of the self-propelled vehicle is fully acknowledged by road authorities and their engineers. There is no desire on their part to suggest unreasonable restrictions, antagonistic to such traffic, but, in the author's view, some modifications in design could be made, particularly in connection with maximum loaded axle weights, wheel diameter and speed.
The financial burden of the necessary adaptation of roa.ds is far too serious to be borne entirely by local iates, and should be adjusted between vehicle owners, lodal ratepayers, and the State. The steel-tyred vehicle is the worst offender, being very injurious both, to bituminous roads and to sett-paved roads. On roads other than those paved with granite setts, motor omnibuses form the most destructive traffic with which the road engineer has to contend.
In the author's opinion, motor omnibuses and heavy motors should make some reasonable contribution towards these additional expenses. The motor omnibus should contribute from 25 per cent. to 33 per cent. of the cost of adaptation, where it is necessary, and an addition of twopence per vehicle-mile towards maintenance. Heavy motors should pay a licence duty equivalent to about a penny per ,vehicle-mile. The author's proposals may be summarized as follow :
The Surveyor's Proposals.
(1) That the minimum diameter of 4 ft. recommended by the Departmental Committee for wheels fitted for steel tyres for an axle exceeding six tons in weight should also apply to wheels fitted with rubber tyres. (2) That steel tyres on heavy motors should be entirely prohibited. (3) That the' car should be designed so that, when loaded, the centre line of the load should be sufficiently in front of the back axle as to ensure the maximum load being 'carried without exceeding the maximum single axle weight. o te. —In several designs of motor wagons the centre line of the load is behind the back axle, and from 70 per cent. to 75 per cent. of the total weight of theioaded car is on the rear axle.
(9) That, if fitted with pneumatic tyres, the speed of heavy motors, not exceeding six tons in weight, might be increased. to 20 miles per hour, and those exceeding six tons to 12.miles per hour.
(5) That heavy motors, other than motor omnibuses, should be annually licensed subject to the payment of fees, based on weight and power, or on a mileage basis.
(6) That motor omnibuses should be similarly licensed and subject to a fee of twopence per car-mile, and should contribute towards the cost of adaptation where adaptation is necessary. (7) That as regards motor omnibuses, the provisions of the Local Government (Emergency Provisions) Act, 1916, be made permanent. (8) That motor chars-it-banes trading from centres, although, not picking up passengers en route, should be sub3ect, to the same regulations in respect to licence fees as motor omnibuses.