The Problem of Road Construction.*
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The Necessity of a More General Regard ior Modern and Future Requirements.
Following so closely upon the reading of Mr. Howard Humphreys' paper before the Soziety of Road Traction Engineers, this one upon other features in the an-important road question tends to show how widespread is the interest in the subject. The authors began by referring to the alternating periods of activity and neglect on the part of road authorities, and next referred to the interregnum between the dates of the universal extension of railways and the advent of motor traffic. They expressed the viaw that our roads had gradually become inferior, until they were only suitable, ten years ago, for the very moderate amount of horse-drawn traffic which was then to be found upon them.
Attention was next directed to the fact that any further increase of railway traffic necessitated the greater use of the roads for " feeder " and distribution purposes, quite apart from the differences that had been introduced into the problem by the greater speeds and greater axle-loads of selfpropelled vehicles.
The Need for Imperial Aid.
A considerable section of the paper was devoted to this topical aspect of the question_ It was pointed out that rate-paying possibilities in country districts cannot bear a further rise in expenditure, even if they can continue to meet the existing charges, whilst nobody can assent to the view that finality in regard to motor traffic has vet been reached. In these circumstances, the aethors regarded it as a natural corollary that local authorities should pass resolutions, as they are doing, to the effect that they cannot maintain the roads without grants in aid. They considered that such disbursements should be coupled With effic'ent supervision as regards the application and use of the money.
The Road and the Wheel.
The authors here quoted from the " Kinematics of Machinery " by Professor Reuleux, to whom they attributed the first true conception of a machine, and our ine sent realisation that the action of a rope on a pulley, water in a hydraulic system, or a wheel on a road, might be considered as much cases of mechanical action as the case of a pair of toothed wheels working in contact with each other.
Proceeding, they emphasised the necessity for equal regard to the condition of the road as to the perfectien of the wheel which travels over it, and the construction of the road so that there might be neither temporary nor permanent deformation. They dismissed the metal-surfaced road, on the score of the lack of its ability to provide the necessary adhesion on gradients or for efficient steerage, and condemned both asphalt and wood, so far as their general adoption is concerned, on the score of cost. Before proceeding to elaborate this portion of the paper, the authors showed some diagrams, and supplemented their views by means of lantern models.
Waterproofed Roads.
The waterproofed road was strongly advocated, by reason of its yielding both a dustless surface and a body capable of withstanding disintegrating influences. The paved road, with granite setts laid upon a concrete foundation, was
• Ical to be both costly and liable to superficial unevennesses, the latter, though comparatively unimportant for horsedrawn traffic, owing to its lower rates of speed, being most destructive in the case of motor-wagon traffic. They regarded the use of irregular granite cubes, such as the " Kleinpflaster " and " Durax " paving, as only likely to be adapted in special cases, and they laid down, as the advantages precedent for good road construction : (a) the tee of as hard a stone as can he obtained at a reasonable cost; (b) the filling of the interstices with a material as nearly as possible of the same nature as the stone itself ; and (c) the binding together of the road crust with something better than dry mud. They criticised the use of crude oils, and of unprepared tar, and expressed the view that the Gladwell system of road construction was the best in existence at the present time. We quote a portion of the authors' paper here :
Mr. Gladwell uses a suitable tar preparation to make a matrix with fine granite chippings. He lays this matrix on the old surface of the worn road to a depth of Lt to a inch. He then spreads the broken road stone on the top of this to a thickness not exceeding 4 inches, and rolls it immediately with a steam roller. The roller forces the stone down into the matrix and squeezes up the matrix into the interstices, and, if they have been laid in the right proportion, but little rolling will bring the matrix almost up to the surface. A small quantity of matrix can now be laid over the surface, and brushed in, and a final rolling will produce a thoroughly waterproof surface. The coat of this system need not exceed at peace per super. yard above the cost of a similar coating of granite on the old water-bound system, and it is known that it will last twice as long, and under various more favourable conditions, possibly from three, five, to even seven times as long. Mr. Gladwell has thus produced a system of road construction that is applicable to all the . roads of this country, and which will enable surveyors to use heed material, if it is not of too soft a neture, and to produce roads that will be unaffected by the temperature or by the weather, and strong enough to carry anything in reason that may be put upon them. At the same time, . the stones will he securely held in position, and there will be no dry mud to be sucked out of the interstices by the pneumatic tires of motorcars. It looks as if the destruction of the roads by motorcars can thus be completely obviated, and almost the only source of wear to this kind of road surface will be the attrition of horseshoes and the steel tires of horse-drawn vehicles. The rolling contact insult! by self-propelled traffic on rubber tires seems likely to produce little appreciable wear or injury to such surfaees, and its waterproof nature saves any necessity for scraping or scavenging other than that which nature supplies by occasional heavy rain storms. The system of Mr. Gladwell is the latest and apparently the most satisfactory. The authors have had no hesitation in speaking of it in warm terms, and they would support the Roads Improvement Association, which has recently issued a pamphlet, giving a description of it and advocating its adoption. It should be said that this system is not in any way protected by patent rights, and there is a large range in the choice of different binding materials which can be adopted in connection with it. It may not, of course, represent finality, and it is obvious that in eaeh district there may be certain modifications dependin, upon the material available, and the peculiarities of local traffic, but at any rate it appears to the authors to offer the best solution yet proposed for a standardised system of road construction, at reasonable first cost, and only moderate charges for maintenance.
In conclusion, the authors pleaded for the general adoption of still wider tires and still larger diameters for the wheels of motor wagons. They also pointed out the beneficial results of careful driving in respect of avoidance of travelling in the same tracks day by day.