Colonel Crompton 's Manchester Paper.*
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The Discussion.
The President (Dr. Ed. Hopkinson) said the paper was of intense interest and of very great importance in connection with engineering questions generally. It. dealt with one of the oldest problems which engineers had been called upon to solve, and it brought out very clearly the fact that the question of the construction of the read could not ba separated from the other question, the construction of the vehicles which were intended to travel along the road. They were two parts of one problem. It had, been generally supposed that the construction of the road was a matter for the civil engineer, and that the &Signing. of the vehicles fell within the province of the mechanical engineer ; but, after hearing Colonel Crompton, he (the President) was inclined to think they were both matters for the mechanical engineer. The fact that mechanical engineers were now taking them up gave good .reason to hope for a very great improvement, which would be of enormous advantage to the nation at large. Colonel Crompton spoke of the wave effect produced upon the roads. He would like to draw attention to the somewhatanalogous case of the ripples formed by the waves advancing on the sea-shore. The conditions were somewhat different, because water was an inelastic fluid; but the motion of the particle of water relative to the land was identical with thu motion of any particular particle in the tire of a wheel relative to the road. It was a circular motion, but at the same time advancing. In general, the characteristics of the ripple mark were the same as those of the wave mark upon
the road. Anyone who had spent a winter in Canada or Russia, where the snow lay on the ground all the winter, would have noticed how the roads there assumed a most extraordinary wave formation quite early. How that came about hard not been fully explained, but his own impression was that it originated very soon after the first falls of snow, when the vehicles were still wheeled and had not been replaced by sledges. In Russia, during the winter, all vehicles had the wheels taken off and sledge runners were put on. The pitch of the wave was just about the same distance as the horses' tread, as though the indentation, once formed, was much magnified by the horse stepping out to the same distance as the length of the wave.
He would ask Colonel Crompton whether, in his experience, he had found that the crest of a wave, once formed, progressed along the road in the, course of time. He thought that must be the case if the crest was being consistently bombarded by the wheel, as Colonel Crompton had explained. Could the crest he broken down? He thonaht that must be so. Possibly one reason why the smaller particles were found in the hollow of the wave was that they were broken off by the bombardment of the crest, He also asked Colonel Crompton to give them a general idea of the cost per square yard of forming a bitumen road on the surface of an existing macadam road. Probably the figure could be got out from the data given in the paper, and it would be interesting to have the comparison. The most. important part of the paper was the description of the author's discovery of the differences between pitch and bitumen. In a sense it was epoch-making and comparable with Macadam's discoveries; they in Manchester were fortunate in having the announcement made to them in the first instance.
A Case of Faulty Road Making.
Mr. W. C. Gaes remarked that lie was not a road engineer and would not offer ally criticism personally, but he had gone to a. friend who had charge of the main road between Manchester and Damen. There was more motor traffic on that than on any other road in Lancashire, and his friend had given him figures which showed the tremendous increase which had taken place in heavy motor traffic during recent years. The numbers of journeys made by vehicles of that class iti the course of a year were : 1903 1780 1905 2200 1908 5200 1912 8530
In 1900 about a mile length of road was prepared with granite setts at a cost of £7000, and the authorities got a 50 years' loan. Owing to the increase in motor traffic they had 'Before the Manchesttr Assodation.of Engineers, at the Midland Grand Hotel Manchester.
H16 already had to renew that road, although the loan was not paid a. [The work must have been very badly done.—Fas] For the kind of traffic which used that road granite setts were the best, with a binding material of bitumen, but the cost of it was so great that they could not get sufficient money to do it. Another point was the difficulty of getting granite setts. .The Trirton Urban District. Council had placed an order for granite sets, but, at the rate they were getting them, it would take between 20 and 30 years to complete.
Who Pays ? Weight Per Axle.
Mr. Alex. Gem said they were all interested in baying good roads. Much might be said on what he would term the ethics of the subject, in regard to the injustice done to railway companies and to the ordinary ratepayer who had to provide the permanent way for the 'benefit of the owners of heavy motor vehicles. But apart from that he believed they would not have satisfactory roads until the weight per axle allowed for that class of vehicle was reduced. He did not know what the regulation weight was at present. Colonel Crompton : 784 1h. per in. width on a 3 ft..w heel is the Local Government Board's regulation. Mr. Gem said that seemed to him too great, and he was quite in accord with Colonel Crompton in advocating the use of more than two axles. By introducing more axles they would, of course, reduce the weight. per axle. Colonel Crompton instanced a piece of road outside London which had been laid in the way he explained, and referred to the enormous sum which had been saved to the owners of motor vehicles. Surely those owners ought to make a considerable contribution towards the cost. What effect would the shoes on horses' feet have upon a bitumen road? Would the road be cut up very much?
London Only, or Also the Provinces ?
Mr. J. Nall, jun., asked whether it was suggested that tho described method of forming a crust. should be adopted on provincial roads, or was it merely intended for suburban roads? To have the surface of a country road practically as smooth as that of a skating rink would be imposing another burden on the poor farmer, of whom they constantly heard. Whatever had happened in London, the horse had not disappeared in the north; at any rate for a number of years they must endeavour to provide a road which would suit all kinds of traffic. It seemed to him that a road with so fine a surface would be dangerous for horse traffic, and very difficult for steam wagons in greasy weather. Mr. WA. Ward inquised whether the author had experimented with pitch of different degrees of softness and different percentages of antInaciee oil; also, whether he could give figures as to the comparative cost of laying roads with bitumen and pitch.
Expanded Metals Suggested for Use in Metalled Roads.
Mr. J. G. Walthew said Ile had been much interested in the paper, which might almost have been split into two portions—sme dealing with the advantage of road transport compared with railway transport, and one dealing with road_ transport from the mechanical point of view. In regard to the wave action and the binders which had been mentioned—either bitumen or pitch—he wished to ask whether any experiments had been carried out or any pm:Tee used (similar to the expanded metal which was used in concrete buildings) for the purpose of stoppiag the spread of the mad metal, There were undoubtedly very great possibilities in the future of road transport, largely owing to the big strides made in the development of motor wagons and the like. Evidently the time had come when the roads must receive as much attention in detail as motor wagons had received. Congestion of traffic also pointed to the fact that the motor lorry would be used in preference to railways for dealing with the transport of material through the congested areas for, say, a radius of 30 to 50 miles from the big centres. No doubt if Colonel Crompton had extended his paper he would have given a good many data with reference to the present efficiency of locomotives used for, goods traffic. Had he any actual figures showing what was the *efficiency of a goods locomotive, taking into account the number of hours in each working week when that locomotive was standing idle, and the number of journeys it had to make when it was not
coeveying material, but mooning about from place to place getting ready for conveying material?
Colonel Crompton; Are you speaking of the locomotives 011 railways? Mr. Wa!thew assented, and added that. it seemed to him the efficiency of locomotives must be very poor.
How Bitumen Lasts.
Mr. L. Hollings stated that in Cherlton-cum-Hardy (a suburb of Manchester) a road was made 16 years ago with bitumen biading material, and other roads had been made with a pitch material. The former was now in a very much better condition.
Drivers Prefer the Tramway Track.
Alr. F. J. Harris, after thanking the author for his paper, referred to the statements that the cost of rubber tires for motors was very great in England on account oh the attrition, due to the manner in which most roads were payed, that roads should be paved with suitable material offering the least frictional resistance (bearing in mind, ef course, the initial cost), and that bituminous compounds were the best and most economical. No doubt all the members were aware that highway authorities were attheir wits' end to know how to provide .suitable roads for the ever-iecreasing motor traffic. On the main roads the drivers of motor vehicles would deliberately leave a good paved carriage-way and run on the tramway track, because the metals offeredthe least resistance to the car; the result. was that the paved margin on each side of the train rails were much more rapidly than the paving in the rest of the roadway, and additional expense was thrown upon corporations and companies.
In the paper, reference was made to a machine for testing road pavements. Was it possible to arrive atthe life of stay material for a given tonnage? If so, what was the life of a road of which the foundation was cement concrete and the top surface was covered with rock asphalt 2 ins, thick, taking the tonnage passing over it at approximately 2000 tons per day of 12 hours, a.nd assuming that the motor wheels were hooped with iron? He had given thesubject considerable attention, having in view the prohibitive cost of paving the whole width of roadway with suitable materials to resist heavy motor traffic, and he had come to the conclusion that the problem of dealing with heavy motor traffic would be solved if tracks were specially designed and laid down at a reasonable cost on each side of and' forming part of a. roadway. The owners of motor wagons would not object to paying increased rates or licences as a contribution towards the cost of stich a track, and it would be beneficial to all concerned.
No Inducements Now to Use More Axles or Larger Wheels.
Mr. D. H. Simpson said the main difficulty in road construction was that the conditions for road traffic laid -down in the Local Government Board reguluLions wr.re inelastic enough to permit engineering design to cape with the destructive action of concentrated driving-axle effort on the road. The adoption of six wheels was out. of the question, owing to the restrictions on tare weight imposed by the Act, If the axle-weight had been the limit, a multiple-axle vehicle could have been produced; it would have beets an engineering problem. A greater proportion of paying load could be carried on vehicles with a. much less destructive sadion on the road.
The question of wheel diameters was now very much matter for the rubber-tire maker. At present-, there was no advantage in using a larger rubber-tired wheel, because the tire was guarauteed by the manufacturer, who would supply a tire at so much per mile irrespective of the diameter of the wheel. If the tire makers made a rebate on larger tires, there would be ROLMe inducement, for owners to use larger wheels, but at present everything was tending towards the use of smaller wheals; the limit; of tare made a large wheel practically impossible.
Colonel Crompton's Reply.
In replying to the discussion, Colonel Crompton said he had never been heckled in a more friendly way, and it was easy to answer the questiors which had been staked. Those put by the President were the most difficult.
The formation of very marked waves in the snow, apparently made by el-edges, was a very puzzling problem indeed, even more puzzling than the President seemed to think. It occurred where mud had been hardening gradually and sledges had been used from first to last. He believed it, had something to do with the same act-ion as that of the wave formation by road rolling. The material was pushed to a certain extent until it began to take hold of the firmer ground and could be pushed no further; then, either the wheel, or the sledge, had to mount it, and proceeded to push a fresh lot along. It was complicated enough with a wheel, but still more complicated with a sledge. He would like to think, with the President, that it was caused by the wheel first, and accentuated by the, sledge: but there were cases where it had been caused by the sledge alone. At present, he could think of no explanation other than the pushing forward of material up to a certain point: -It was analogous to raking large quantities of soil: one pushed it to a certain extent and could not push it further; the friction of the heap against the soil became too great, and the rake passed over it.
Moving Crests on the Highway.
With regard to the question whether the crest progressed or moved in'the direction of the traffic, he was perfectly eon
&lent that it did, but he could DMswear to it In one or two cases he was certain of it. He knew of cases where us ripple was formed in the wake of a projection on the road, as a ripple was formed over _a stone in a stream; it started as a small ripple in the road, and then progressed. They could see it increase day by day ; they could see the crest come down the road until it got to the pitch: Another question was whether the' crests broke. They did, just as the crest of a water wave broke. When forced to a certain extent, it cracked_ at the top and the stones broke oat. The action of horse traffic kicked the stones out and let the water in out-he crest, and in time repair because absolutely necessary. In all probability, in some cases, small particles had been projected and tilted over, and these fell again into the trough over the crest. But he was able to sac' confidently that as a rule there was a collection of smaller stenos solder the trough, and large stones under the, crest.
Less Camber Wanted.
Reference had been made to the effect of broad tira.3 (presumably steel tires) on a road with considerable camber, It was a well-known difficulty, and could not be met easily by any particular design—even by haviag the axle in two parts. On modceas roads, they could do with very much less camber, instead of the 1 in' 15 or 1 in 18 which was quite common near the channels to the road. The Road Board regulation was 1 in .36. With such a ro.id as he was advocating, they could go to as high as 1 in 40 without much fear of water being retained on the read.
The Importance of Good Roads.
Thee, as to the .difficulty of gettai»g granite setts. His
opinion was that the whole sett .faisiness was a mistake. Ile " went. the whole hog,' and would say he could get sandstone rock and crush it down into the kind cwl sand he wanted, which was far cheaper and made an infieitely better and more elastic road than with granite setts. The read being slightly elastic, all these troubles were much lessened.
Mr. Gass entered into what he would cad " road politics." Well, he (Colonel Crompton) was an engineer, and not a politician, and he was not going to say where the meney was to be found. As -engineers they had to keep clear of that. Somebody had to pay for the roads; whether it should be the motor-wagon owners or the community he would net say: Any attempt to make one particular class bear the whole cost would be a mistake._ Good roads were as great a necessity as any other communal thing, and the cost had to be spread over the whole. They were not able_ to remove the burden from the ratepayers in connection with the, maintenance of roads, they were, forbidden by law to do that; but what they did was to apply the money found by motor owners in the shape of petrol tax amilicence tax towards the improvement of the reads, so that in future the upkeep would cot less. That was as far as the Road Board could go. He agreed with Mr. Gem in regard to axles. On the present. roads they had ss well-designed method of making up
the surface, and with a reasonable system of traffic regulation they could make them carry enormous quantities of traffic— far in excess of what was possible nowadays—at a comparatively small cast.
Good for the Horse.
He asserted confidently that Mr. Nall was mistaken in thinking the farmer was going to suffer because the roads would be made smooth. Everybody who had considered the subject knew that bituminous roads would be much better for horses than the roads in the West Yorkshire district with which he was acquainted. If the horses were shod properly, there was no trouble in designing a road on which the animal would not slip at all. On the Kingston Read, constructed on the principle he advocated, 5000 to 6000 tons of stuff were carried each day, and when a horse was taking a far bigger load than he had ever taken before he never slipped the sixteenth of an inch. That was the answer to Mr. Nall: they would benefit the horse mere than anybody else.
Increasing Supplies of Bitumen.
Mr. Ward asked what was the comparative cost of laying a road with pitch as against. bitumen. He did not hold a brief for either material, and he was far from saying they could not make an extremely-good road with pitch ; but it was much easier to make a good road with bitumen than it was with pitch. At present, pitch was about three-fifths the price of bitumen, but, if things went on as they were doing, it looked as if the two materials would be the same price. There was a very great demand for pitch, a demand that was not falling off, and the supply was not increasing. There was also a great demand for bitumen, but the supply was increasing by leaps and bounds.
A Time when Roads will be Goad Everywhere.
Mr. Walthew asked whether the wave action could be countered by expanded metal or reinforced metal. The answer was, Yes. Roads with concrete base and bitumen above had hitherto been a luxury confined to large towns where the traffic was exceedingly heavy, and he had never contemplated
going to the cost of that in the country districts. Of course, they could not transport goods all over .England without going upon country roads, and, if his address that evening had any meaning at all, it meant that they were looking forward to an era when the roads would he good everywhere, that was to say all the main roads between town and town connecting districts together, along which produce would come into the great centres of population. The main problem was to deal with the roads outside towns, where the money spent was not large.
2000 Tons of Traffic a Day a Mere Trifle.
Mr. Hollings asked for data as to the life of a road such as was referred to in the paper. That question was put to him almost. every day by surveyors, and he gave very guarded answers. They could not be prophets until they knew, and they had to live long before they knew how a road would wear. Perhaps he would never know Irow long many of the reads in London, constructed to his specification, would last, but. with a wearing surface an ineh thick they ought certainly to last 15 years, or something like that., with 2000 tons of traffic per day, which he considered a mere trifle. Over one road which he had constructed, 9000 tons a day passed, and it had not been marked in 18 months; they could not measure any wear on it. Therefore, he would say that, with an inch on the top of the road it would last at least 12 years ; it ought to last even longer.
Make the Road the Same All Over.
What he would term "tracking " was suggested by Mr. Harris, but his opinion was that it was better to make all the road alike; anything like tramlines in a road would increase the wear near the tramlines. If they made, a road the same all over, they encouraged the traffic to use every inch of it, and the better it was for the ratepayers and all concerned. In reply to Air. Simpson, ho might say that at the present moment they had under consideration an address to Mr. John Burns asking him to modify the regulations which were at the root of the whole troubre. The maximum weight of tha vehicle was wrong; it ought to have been a maximum weigh: per axle.