Effects of Motors on Roads.
Page 15
Page 16
If you've noticed an error in this article please click here to report it so we can fix it.
The last meeting, for the session 1907-8, of the Incorporated Institution of Automobile Engineers, was held on Wednesday the r3th instant, at the Institution of Mechanical Engineers, Storey's Gate, St. James's Park, S.W. The president, Mr. Dugald Clerk, F.C.S., M.Inst.C.E., took the chair at 8 o'clock, and, after the usual business of announcing the names of new members elected, Mr. W. J. Taylor, the County Surveyor of Hampshire, read a paper on "The Effect of Motors on Roads," dealing with the question from the road engineer's point of view, whilst the road user's side of the question was taken up by Mr. Douglas Mackenzie, A.M.I.Mech.E., M.I.A.E. These two parties, road makers and road users, have long been throwing mud at each other, and using every possible form of argument in their endeavours to put the responsibility for the bad condition of the roads on to the other party. Recently, however, we have had the satisfaction of knowing that the two factions are showing an inclination to meet and discuss the question in a scientific manner, in the hopes that they may, in the near future, come to an acceptable and practical solution of the problem.
Action of Tires and Studded Treads.
At the meeting last week, Mr. Taylor opened his paper by a short exposition on the physical characteristics of our roads, and particularly mentioned the origin of the many and dangerous corners which are to be met with in all parts of the country. He then went on to point out that any increase or expansion of the traffic on a road, whether it be self-propelled or otherwise, must obviously cause increased wear of the road surface, augment the abrasion of the crust, and hasten the development of any weak spots in its construction. After lightly touching on the subject of wheel diameters, and their effect on the road surface, the author made the following statements :— "In regard to light cars, it is usually conceded that on good macadam roads, ordinary pneumatic tires, as a rule, inflict little damage ; but on roads of flint and gravel, or other poor material, the suction of soft tires draws out the finer and loose particles from the interstices, and thus tends to unkey the metalling. The effect of armoured tires is, however, very different." " When the tires are metallic, the shocks are evidently more violent than those with india-rubber; further, some makers have furnished their wheels with rows of studs; then, the effect produced is frightful ; ir is nothing less than a large toothed cog-wheel; the roads are, so to speak, ploughed up."
"The high speed of light cars is very destructive to the road, as the leaping motion acquired by the vehicle lifts the driving wheels from the surface, or, at any rate, so reduces the friction at the point of contact that there is slip,' and the metal is filed out of the road in a series of small depressions."
Cross-fall or Camber.
There is no doubt that most drivers have a tendency to drive their vehicles along the crown of a road, and, although this is often due to the presence of weak spots in the sides of the roads, there are many drivers who persist in keeping to the centre of the road even when the sides are in good condition, and the camber is not excessive. Mr. Taylor complained that Parliament had legalised the use on the highways of traction engines, and, later, the motorcar, without first ascertaining whether the existing roads were capable of carrying the new form of traffic, or giving the road makers a chance to improve their highways. We are of opinion that, had Parliament waited for the road engineer to make good his roads, neither this generation, its children, nor its children's children would have ever seen the motor vehicle on the public highway. In many parts of the country, the roads are being improved as regards their cross-fall or camber, but the completion of this work, like that of providing proper foundations, and the use of better materials for road making, must necessarily, on account of its cost, occupy a considerable time. The author appealed to road users to cease using studded or other forms of destructive tires, and to make more uniform use of the road surface.
Foundations.
Undoubtedly, the most serious fault in the construction of our roads is the lack of anything in the nature of a "foundation." Mr. Taylor went on : " Since.the days of Telford and McAdam, text-books on road construction have explained to the engineering tyro that the proper method of constructing a road is to put in a solid foundation of handpacked stone of large dimension, on which to spread and consolidate the surface material ; but, unfortunately, this method is, after the lapse of generations, still mostly confined to the text-books." The author stated that he recently had instructions to put in a substantial foundation to about ten miles of main, road, and, after doing so, and making the foundation from 6 to 14 inches in thickness, the cost was found to be so great—about .4-r,000 a mile—that it was considered much too expensive a form of road for all but special cases. It is in consequence of such costly constructions as the one he outlined that, the speaker stated, road makers are compelled to be satisfied with the more unsatisfactory method of " accumulating " a foundation, by laying down each year a little more material than has been actually worn out by the traffic on the road, and gradually to increase the quality of the material used. Giving examples from the records of his own roads, Mr. Taylor said that, whereas, in 1898, he was using on certain roads ro6.5 cubic yards of material, made up of 105.8 yards of inferior materials and 0.7 yard of superior materials, he is now, in tgo8, using for the same roads 84.1 yards of inferior materials, and 49,8 yards of superior materials, or a total of 133.9 cubic yards per mile of road. The superior materials are made up of basalt, granite, and syenite. This change has sent up the road bill by just over too per cent., but the surface and the cross-fall have been considerably improved, and the foundation, by reason of the " accumulated " material, has also been slightly strengthened.
Tarred Roads and Dust.
Tarred, or otherwise treated roads, next occupied the attention of the audience, and, after Mr. Taylor had given the history of such roads, we were pleased to hear him make the following statements :—
"There is little doubt that a coating of tar does greatly help a macadam road to resist the effects of motor traffic; the binding material is not easily drawn from the interstices of the stones by the suction action of the tire, and the roads derive benefit from the greater or lesser extent to which they are waterproofed. As a method of laying dust, other than that of imported nature, the tarring of roads has met with considerable success, and its employment is rapidly extending, notwithstanding the objections raised on account of the tar's being taken into houses, spoiling carpets, or polluting streams. I need scarcely point out that a most important consideration, from the point of view of the ratepayer, is the extent to which the tar treatment of roads saves wear and tear on the surface and adds to their longevity." "It is on these grounds that I agree with the opinion expressed by Mr. Maybury, the County Surveyor of Kent, and many other road engineers, that the roads of the immediate future—except in towns and special places where costly pavements are warranted or justified—will, for financial reasons, be of ordinary macadam structure, granites, basalts, and other such stones being substituted for soft local material, as funds will permit, and with a surface treatment of tar. Although by consolidating your material in a bituminous matrix of some kind or other, and, to a lesser extent, by tar-spraying, you seal down your surface and reduce dust to a minimum, you still have to deal not only with that which is produced by actual surface wear under contact with traffic, but you have to cope with that most offensive form of dust which is imported on to the road surface, and which can only be entirely avoided by the abolition of horse and other animal traffic from the road. It has proved a distinct disappointment to the public to find that improved forms of road surfaces, such as those we have just been considering, are not entirely free from dust; in fact, there is no such thing as a dustless road."
The Road Users' Defence.
Mr. Douglas Mackenzie then opened the defence for the road user. He thought that the vehicle and the road should be considered as a mechanical pair, and that the road condition should be taken into consideration when the vehicle was being designed. lie said that he had recently spent a considerable amount of time in examining injured roads to which his attention had been directed, and in nearly every case it was possible to trace the cause of the injury. The actual injuries which he had observed all fall under one of the four following heads :--(t) suction due to bad road material; (2) slip due to imperfect adhesion; (3) crushing due to insufficient area of support; or (4) horizontal, rotary movement due to steering or turning.
Suction.
The greatest amount of damage was, in Mr. Mackenzie opinion, caused by the sucking action of the tires as they leave the surface of the road; the evil has always existed, but the higher speeds of the modern vehicles has made the trouble more marked. Improvement in the road surface is the only means of stopping this trouble, and the speaker went on to state that he had often urged that " The system of road construction by which the stones were held in position by mud is quite unsuited to modern conditions, and that roads must now be constructed with a bituminous binding matrix that will adhere to the stones, and that cannot he disintegrated by suction. The objection to such a system -of road construction has always been the question of cost, but the progress of invention has now brought several materials within the field of practical politics, which do not increase the cost of road construction by more than a few pence per super yard, and which remove all risk of injury to the road surface from suction. There is no doubt that in a few years' time the public will consider that any council whose roads are constructed with a water bind are guilty of gross misfeasance in failing to use modern methods."
" In this connection, the recent report of London borough engineers, to the Metropolitan Paving Committee, is exceptionally interesting reading. The engineers were asked to report on the effect of motorbus traffic on roads surfaced with asphalt, wood, and macadam. They are united in stating that no injury to the surface of asphalt or wooden roads can be detected, but they are unanimous in their opinion that motorbuses are ruinous to macadam, and most of them state that this is due to suction. One engineer, however, points out that much of this injury can be prevented by tarring the road, so as to obtain a bituminous bindingto hold the road stones in position, and instances this from a road in his own district."
Slipping of the Studded Tires.
The slipping which takes place between the tire and the road is due, entirely, to the excessive horse-power which it is now considered fashionable to employ on touring cars. In this connection, the author gave a very good example. He said : " The greatest sinners in this respect are the cars with engines above 3oh.p., and fitted with light two-seated
bodies. The author had a practicaldemonstration of the injury resulting from such cars, when a well-known racing man called at the house where he was staving with a ooh.p. racing chassis fitted with a testing body. In moving round from the motor house to the front door, and in going down the drive, he tore up the gravel roadway in six places to a depth of about 2 inches, showing where he had either let in the clutch or opened the throttle. In no case was the adhesion sufficient to enable the car to respond to the sudden increase of propelling force, or to drive the car forward without the wheels .slipping -considerably." . Another cause of slipping was that due to the bouncing of the wheels when travelling over uneven ground. When the wheel is thus momentarily relieved of the greater part of its load, it will spin round at high speed, and simply grind or file out the material of which the road surface is made. The questions of crushing, and the damage due to steering were then dealt with byMr. Mackenzie in a very interesting manner, and he suggested that, possibly, some form of " Pedrail " wheel, on which the feet were free to twist, as is the foot of an elephant, might lessen the damage which is now caused by the sideways movement of the wheels when they are turning corners.
Foundations.
On the subject of road foundations, the following very
interesting report of Mr. J. A. Bean, the County Surveyor of Northumberland, was put in by the reader of the paper. The roads of Northumberland were formerly without any pretence to foundations : "About six years ago, I noticed that heavy traffic was considerably increasing in the county, and that in order to maintain the roads -economically it was important to provide them with a suitable foundation. We carried out two or three miles, and found that it was likely to make a considerable difference to the cost of maintenance, so that we have since adopted the plan of providing about eight miles every year with a foundation. I am highly pleased with the result. The initial expenditure of providing a foundation to a road is always heavy. The total length we have done up to the -present is approximately thirty-eight miles. The cost of the work varies from ic4d. to is. 50. per square yard, according to situation, and this includes all labour, carting, etc. The stones are all hand-packed, and the thickness of the foundation varies from twelve inches in the centre to four inches at the sides. The reason so much stone is placed in the centre is because traction engine-drivers always take the centre of the road, as it is the easiest part of the road to drive upon. The roads in this county for the most part are on a bed of clay, and I. estimate the saving in cost to the county is approxi mately thirty per cent. The above foundations have been made with hard whinstone, as it is the cheapest kind of material one can use, because there is no need to coat the road with smaller stone until the larger stones are seen to 'appear through the surface. With any other softer material this method is impossible, as the foundations would immediately crumble away if the top coating were worn too thin; therefore, so thick a coating (or wearing surface) is unnecessary as with a soil foundation." " We are continuing the work of providing foundations every year, and this I am sure is the right principle to adopt. In speaking of roads with a foundation, I cannot omit to mention again my experience of tar macadam : we have laid in this county eight miles of it. It has been most successful. The labour on the road has been exceedingly small. It has caused us no trouble, and the cost of repairing one length, which was carried out at the end of last year, amounted to aid. per square yard for 9,400 yards, whereas previously the cost for ordinary macadam was Is. per square yard, after being down the same length of time."
A Contrast.
In strong contrast to the above case, a rural district in the county of Nottingham was then quoted. In that district, the Surveyor has used a very porous, honeycomb slag, that was the refuse from a tarmac factory. Needless to say the road gave way when a heavy country carrier's cart attempted -to pass over it. .Mr. MackenzieFs general comments, after mention of this case, were : " Some people will be penny wise and pound foolish to the end of their days, and where they appoint a road surveyor because he has been a failure -as a farmer, and buy their material because it is useless to everyone else:,, and appoint their road men because they are too old for any other work, roads cannot be expected to bear the traffic,. and are certain to cost the ratepayers from three to five -.times as much as.. if they were
properly constructed," • The Effect of Wheel Size on the Roads.
Following the reading of the papers by Mr. Taylor and Mr. Douglas Mackenzie, a very interesting contribution, in the form of a few " Notes on Wheel Diameters " was given by Colonel R. E. Crompton, C.B., M.Inst.C.E., and these were illustrated by two simple diagrams, by the aid of which it was clearly shown how the Local Government Board regulations on the relation of tire-width to the diameter of the wheel were framed. The relation between these two dimensions is such that, under similar conditions of road surfaces, equal areas of road surface are under compression. This being the last meeting for the -session, it was decided that there should not be an adjournment for-the purpose of discussion, which, therefore, was of a verybrief and-superficial nature, as there was no•time left,after -the reading of the papers, adequate to discuss the many points that were raised by the three contributors.