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23rd February 1926
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Page 21, 23rd February 1926 — THE FUTURE OF ROAD TRANSPORT.
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Which of the following most accurately describes the problem?

Recent Tendencies in Commercial Motors and Their Equipment, and the Effects of the Growth of Traffic on the Roads.

By Sir John E. Thornycroft, K.B.E.

1\12Z.P:Paierellshe.diZenr; 6111'

,uestionpossibly conflicting

with road transport at the present time. Therefore some mutual consideration of possible developments ' by engineers responsible for the running of vehicles, engineers making them and the roads they have to run on, should be quite useful.

Recent developments WhiCh have taken place in vehicle construction have, I think, shown that designers have proved themselves capable of producing vehicles adapted for service, not only on good roads but also over countries where only trackways exist.

In this country we are provided with a wonderful system of roads, varying very greatly in construction and quality. There has, naturally, been some conflict of opinion between those who run vehicles and the authorities responsible for the road maintenance and, during the last 20 years or so, numerous inquiries have been held, with a view to minimizing road damage and fairly apportioning the cost of the upkeep.

Road authorities have succeeded in making " the vehicle owners pay very large sums in taxes which, until recently, it had been assumed would all be spent in road maintenance and development. It is not a title to go.into the appropriation of funds derived from the taxation of vehicles, but it does seem to, me very desirable to consider the extent to which road transport is economical to the community as a whole.

It is evident that the railways are beginning to fear competition and 'are getting perhaps a little jealous.

A Legitimate Place for Road .Transport.

Engineers will not dispute that there is certain work which the railway companies can legitimately do, which road transport cannot economically compete. with, but this should not prevent our considering how far it is more economical to do other work, and the mere fact that a large amount of money has been invested in railway companies should not bar develop ments of road transport. In other industries new methods are constantly being introduced and nothing prevents money being invested in some alternative form of plant if it is capable of doing the work more cheaply and better.

Road transport ranges from the conveyance of one or two people in quite a small vehicle to the transport of 50 or more passengers in an omnibus, and from a few parcels to as much as ten tons of goods.

Legislation has, undoubtedly, had a great influence on the type of car produced in this country and the War Office subsidy schemes have also determined to a great extent the types of goods-carrying vehicles.

The size of vehicle which was Selected for the subsidy type prior to the war (of a nominal capacity of 3 ions, but it would really take a good deal more), was made in such very large numbers during the war period, and such a" large proportion of them have since

• been brought into commercial use in the country, that they have necessarily tended to set a standard of capacity. At the end of the war there were about 40,000 to be disposed of and there are still some left.

There is no doubt that about a 4-ton useful load is quite a good one for a great ninny trades and, in spite of the large number of second-hand vehicles which is being used, builders are still getting orders for considerable quantities of new ones of the same capacity. The different makers in this country vary in the transmission gear they use; but the chain drive has practically disappeared. Some prefer a bevel drive to the back axle, but the Worm appears to predominate in this country. On the Continent it is not used to any

thing like the same extent, neither is it in America for the heaviest types of vehicle, although in very general use for the lighter ones.

The fact that there are many thousands of ex-War Office vehicles which have now been at work for 9 or 10 years fitted with their original worms and worm wheels, is a pretty good proof that, when properly designed, they are an excellent means of transmitting the drive.

There are, of course, a great many vehicles suitable for greater and lesser loads than the 3-ton type in general use, besides light delivery vans and, during the last couple of years, the new War Office subsidy scheme for 30-cwt. vehicles has tended to make a pneumatic tyred vehicle, capable of carrying a net load of 30 cwt. at a high speed, a very favourite one.

The Efforts of the War Office to Reduce Tare Weight.

It is of course, advantageous to keep the tare of a vehicle as low as possible provided lasting qualities are not sacrificed. By strictly limiting the weight the War Office have induced builders of chassis to improve their designs and have forced them to use the highestgrade steels arbd materials generally.

There is no doubt that the automobile industry has had a marked influence in the production of the steel which is obtainable to-day and which permits of much greater stresses than was permissible when road vehicles were in their infancy 20 years ago. Then a stress in an axle or other part subject to reversal al strain was limited to about 31 tons per square inch. To-day it may be safely doubled.

It is obvious to everyone that the speed at which goods-carrying vehicles run has increased enormously during the last few years and that the 12-mile limit is now,by general consent, regarded as almost as much a back number as the red flag which a man used to carry in front of a vehicle.

From an engineering point of view there is no reason why vehicles fitted with pneumatic tyres should not run at quite high speeds and, with adequate braking power, 30 miles an hour is not unreasonable for a 30-cwt. load. For the heavier type of vehicle on solid tyres 20 miles an hour is not unreasonable when the tyres are in good condition and the vehicle is well sprung, but there are far too many dilapidated old vehicles which are badly sprung, with worn-out tyres, which when driven at a high speed do an unreasonable amount of damage to the roads, and in some cases even to adjacent houses by the vibration they cause. I venture to suggest that the road authorities who complain of the cost of maintenance should, first of all, turn their attention to this class of vehicle as well as some of the heavy steam traction engines shod with cross-bars on their wheels and which are altogether unsuitable for modern road surfaces.

The Public's Preference for the Bus.

Whilst a very great increase has taken place since the war in the number of goods-carrying vehicles and there seems every probability of many more being employed, I think the most striking thing is the way in which the public service vehicle is being adopted. London led the way with, probably, "the best motor omnibus service in the world and a great many other towns have followed and organized good local services which have supplemented the existing tramway systems but, in addition to these, country services have sprung up connecting one town and another to such an extent that it is now possible to go from one end of the country to the other by motor bus, and I think there is no question that, with the improvement of our existing highways and the further development of through-traffic roads, we may look forward to a great increase in long-distance travelling by motor omnibus.

The motor coaches used in the holiday resorts are also becoming of great importance and will no doubt be used in very large numbers, but not to the same extent as the vehicles which do not depend on a seasonal trade.

These different sorts of passenger services all require distinct designs of vehicle. For wofk in large cities, where they are used to deal with very dense traffic, the double-decker as used in London for carrying about 50 people Ir a legitimate place, but by far the greatest field seems to exist for single-deck types carrying either 20 or about 30 passengers. A 20-seated vehicle can be built to weigh under 50-cwt. and not to exceed dimensions which make it handy enough to traverse by-roads without interfering with other traffic. If built within this limit of weight it has the additional advantage that it is not restricted as regards speed to a greater extent than any motorcar, under the Ministry of Transport's proposed new regulations.

Vehicles to carry about 30 passengers vary a good deal in design, and opinions seem to differ very much

as to which is best. Probably there is no really " best " design, and types must necessarily vary to suit local conditions and service,

The Coming of the Low Load-line Coach.

Following what has been done in America, many English makers have thought it advisable to bring out designs of very low chassis. The American designs are not really very different from the chassis of the low loading-line buses used in London, but they are made to appear very different by the bodies which have been fitted, which not only are built to give the appearance of being nearer the ground than they actually are, but also have very little head room. The American omnibuses of this type have been fitted with very powerful engines and have been developed for quite a definite service. Very great lengths of new concrete roads have been made between cities, and high-speed services have been established to take passengers practically without change to and from places often 50 miles apart. These roads are so 'well graded that road clearances of less than 6 ins. or 7 ins, seem to he sufficient and the very low bodies apparently give a feeling of security to the passengers when the vehicles are being driven at 50 or 60 miles an hour.

Regular Long-distance Services.

The time may come when we have suitable roads to permit of similar speeds but, at the present time, it does not seem there is any reason to follow closely the American example, although it must be admitted that some of these 100 or 150 h.p. vehicles are very fine machines. I have ridden in them myself for distances of 50 or 60 miles at a stretch and found them very comfortable, in fact, a good deal more comfortable than a journey between the same towns in the ordinary railway train, the fares being the same but the time taken in the omnibuses rather less. If one makes such a journey on a snowy slippery road, largely in the dark, one is apt to feel that there must be considerable risk, but apparently accidents do not occur often enough to make people hesitate in the least to ride in the coaches, and, for several years now, a regular service has been maintained from San Francisco to Los Angeles, which is about the same distance as from London to Glasgow, which is timed to average a speed of 35 miles an hour, including stops.

For high speeds, pneumatic tyres and very good spring mounting are, of course, essential. Some makers are adopting something rather like a bogey for their driving wheels. This, of course, has the merit that, when going over uneven ground, the vertical motion of the body is greatly reduced but, for really c38

good roads, is a question how far the extra complication is necessary. American builders of this type of vehicle told me that the American public believe that a railway coach should ride on a bogey and they consider tht same argument applies to a road vehicle, and, if the American public got this into their heads, they would not ride over a single axle and builders would be forced to adopt it, but I think it is doubtful if the British public would take quite the same View. There is no doubt that, for certain purposes, what is known as the rigid 6-wheel type of vehicle has great advantages, and it has been proved that the reduction in the load on the wheels would enable it to compete with the Kegresse or other track type in places where roads, in the true sense, do not really exist.You have no doubt heard that a vehicle of this type has made the journey from one end of Africa to the other, and, for undeveloped countries, there seems little doubt that the arrangement has a future.

Axle Weights and Six Wheels.

From the point of view of the builder of the vehicles or those who run them in this country the adding of an axle may seem an undesirable complication; road makers may, however, take a different view, and it is interesting to consider the effect it has on axle loads. If we take an average 28-seated omnibus designed to comply with the proposed Ministry of Transport regulations as regards overall dimensions and overhang of body, the load on the front axle will be about 40 cwt. and the rear 80 cwt., and if we assume the vehicle fitted with two rear axles and the same mean wheelbase the load on the three axles will be approximately equal, namely, 40 civt. on each, but an axle load of 80 cwt. does not seem enough to warrant the complication necessary to secure a reduction. A doubledeck omnibus with a correspondingly greater load might be more suitable for a. six-wheel arrangement, but as a rule double-deck vehicles are only used in large cities where the roads are.constructed with a view to taking heavy axle weights. The Ministry of Transport regulations as regards overall length are not yet law, and it is possible that if the advantages of the rigid type six-wheeler had been considered a greater overall length would have been permitted for them.

In considering the economics of transport by road, one must obviously take into account both the cost of the transport services, made up of the running costs of the vehicle, depreciation, etc., and also the costs connected with the roads on which they run, but I do not think anyone has, as yet, discovered a method of correctly applying the road costs, and the most we can do at the present time is to arrive at some general conclusions.

Building for the Water-bound Road.

We know that on the first-class town roads heavy rubber-tyred vehicles do very little damage, and that the same vehicles, if the traffic is sufficiently intense, will very quickly ruin roads of water-bound macadam.

Happily the road authorities have recognized that water-bound macadam is no longer suitable for the construction of main roads, but there will necessarily remain a great proportion of the roads of the country over which motor vehicles will travel where tills of road will continue to exist, and the question of how builders of vehicles can co-operate with the road engineers to minimize the cost of maintenance will be of great importance for some time to come.

The wear and tear of roads is dependent both upon the travelling load and the speed at which it is moved.

The speed is in the hands of the driver of the vehicle, but the travelling load, being made up of the weight of the vehicle and what it carries, is dependent on the skill of the engineers who produce them,

It would appear from what politicians are saying that it is being taken for granted by them that the heavier goods-carrying vehicles are responsible for the greater part of the road damage.

No doubt heavy axle loads on unsuitable roads are responsible for an undue proportion of damage. But engineers, I think, will agree with me that the total of the ton miles applicable to the different types of vehicle, qualified in some way by the speed, is the correct way of arriving at their share of responsibility.

There may be figures available which will enable a comparison of this sort to be made, but until it is done I do not think we should accept the assumption that the heavier vehicles are responsible for the greater part of the wear and tear upon the roads.

• There is one thing about the goods7carrying vehicle which is greatly in its favour. I have pointed out that the designer is, in a measure, responsible for the road damage, inasmuch as the gross moving load depends on the weight of. the vehicle he provides. He has been able to produce machines which on the average carry a load about equivalent to their own tare weight. Taking the case of the heaviest vehicle which can be run legally under the present regulations, there are examples of a 101-ton load being carried on an articulated six-wheeler with a tare weight of only 81, so the ratio of tare to gross weight becomes 0.45. If we take an average 5-ton lorry it will be found that the tare weight is about 5 tons, giving a ratio of 0.5.

The 30-cwt. War Office subsidy vehicle weighs 43 cwt., with a 10-cwt. body allowance, and so the ratio in its case is 0.59. In the case of cars the useful load does not approach the tare. Some of the lighter models have a fairly good 'ratio, but, at the other end of the scale, with cars weighing over 2 tons, it will be found that the ratio of the tare to the gross is as much as 0.8.

Should the 14-ton Laden Weight be Legalized ?

I have suggested that, in the case of most city roads, -there is ample strength to take the heavier existing axle loads and that it is not worth while to multiply • axles on the vehicles using them. A great many of

• the heavier freight vehicles which do comply with the maximum axle loads of the existing regulations are, I think, regarded by road engineers as reasonable, but there are others on the road at the present time which, fully laden, do not comply. The suggestion I have made for computing the responsibility for damage between the heavier and lighter types on a ton-mile basis can, of course, only strictly apply when the road foundation is sufficient to take the weight of the vehicle without collapsing, and there are, of course, a much greater proportion of the roads of the country which are capable of supporting the lighter t3pes than the heavier ones. Whether the increase in axle weight from 12 to 14 tons laden weight, which it is proposed to legalize by the new Transport recommendations, will be an economic thing to 'do, is open to question.

Referring to details of design which aro common to . both goods and passenger vehicles in this country, combining the• engine and gearbox to form a power unit is becoming very general. Dr. Lanchester was the first to do it, but it was the general practice both in America and to a large extent on the Continent before here. It has many advantages, and now that it is kriown how to make clutches which do not require frequent Attention, it is difficult to see any real objection to the arrangement. As usually designed, the gearbox itself can be .removed from the motor as a complete unit and it is as easy to detach ft as it was the older type from the chassis and disconnect it from the clutch. The arguments that apply to the smaller vehicles hold good for the larger ones as well and, where the arrangement of a completely separate engine and gearbox with the clutch between is still being fitted-, it will generally be found that the reason is the desire to continue to-use the gearboxes which have been the makers' standard for some time past.

I have already mentioned the greatly improved material which makers have available at the present day, but I do not think, • outside the circle of those who are intimately acquainted with motor vehicle construction, that it is known that heat-treated alloy

steels are being used for shafts and other parts 'that

have an ultimate strength of 100 tons per square in. and a yield point of 90, and that gearwheels made of what is known as direct-hardened nickel chrome steel have an ultimate strength of as much as 110 tons and a yield point of 95. ]for valves and certain other parts which are subject to corrosion, such as pump spindles, rustless or stainless steels are being used with very satisfactory results. All sorts of alloy steels have been used for the springs, but silk° manganese seems now to be generally recognized as the best. In the raotorS themselves the tendency has been greatly to stiffen up crankshafts to avoid periodic vibration and to standardize on side-by-side valves, Provided an equally good consumption and performance can be obtained, the simplest arrangement must be the best, and there seems little doubt that this is obtained by the side-by-side valve and detachable cylinder head.

Magnesium in Weight Reduction.

With a view to reducing the stresses in the moving parts, and also to enable higher compressions to be used without pre-ignition, many firms have been trying aluminium pistons and some duralumin connecting rods. It was interesting to note at the recent Motor Show that, while the American vehicle builders did not appear to have adopted them to any extent, practically every British, and most of the Continental firms, showed aluminium pistons on their stands.

It may not be known generally that aluminium is being used instead of cast steel by some people for road wheels of quite heavy vehicles, and that it is possible now to get a material, viz., magnesium, which is quite as strong, two-thirds the weight of aluminium and no more costly for the casting.. It has been known for some time that magnesium castings can be made, but it is only quite recently that any firm has been ready to take castings for such things as engine bedplates and road wheels in this material. A great deal of attention is being given to different methods of braking and advocates are to be found for every alternative arrangement. Braking on all four wheels is being urged by many people. The commercial vehicle is unlike a: car in that a much greater proportion of the load is carried on the driving axle and there is, therefore, as a rule ample adhesion to give the necessary braking effect on the driving wheels alone, which is not often the case with a car. Some of the foreign makers who have had the greatest experience insist that braking through the transmission Is the right way if it is constructed properly so that It will stand, and say that to add any complication to the steering wheels is fundamentally wrong, but there are now a great many advocates of front-wheel braking and it will be very interesting to see if it is a passing fashion or survives. One thing is essential if braking on all four wheels is employed, namely, that the braking effect should be equally divided, and the most satisfactory way to do this would seem to be hydraulically. it seems probable that, for motor coaches and similar vehicles, the more complicated systems of braking may survive while, for public services and general work, users will demand the simplest possible arrangement.

The War Office and Special Vehicles.

A vehicle which is of special interest in showing what can be done on large_ pneumatic tyres is the Hathi tractor, which has been specially built for the 'War Office, to take a 10-ton load across country or on hard roads.

I do not suggest that there is a wide field for the employment of a vehicle of this type at home, but I think it a useful illustration as showing what can be done to meet certain users' requirements.

[Paper read before a joint meeting at Birmingham of the Institutions of Civil, Mechanical and Electrical Engineers.—En.,

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