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The Road Conference at Olympia.

2nd May 1907, Page 24
2nd May 1907
Page 24
Page 25
Page 24, 2nd May 1907 — The Road Conference at Olympia.
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Which of the following most accurately describes the problem?

Abstracts from the Papers (continued).

A STATE ROAD DEPARTMENT.

The Need Tor and the Services that may be Rendered by it.

By E. J. LOVEGROVE, M.I.0 E. Borough Engineer of Hornsey.

The object of this short paper is to promote discussion of the important consideration as to whether there is need for a State road department, and, if so, to what extent, and in what direction, such a department may be of service, in particular as regards the direct control and maintenance of certain highways, and also in general principle. The direct State control and maintenance of any highways would naturally apply only to such roads as may be considered national or trunk routes, and, in considering the desirability of an alteration from the present county and local systems, there should be no suggestion that such a proposal arises from lack of proper administration by the • existing authorities. The proposal should rather be regarded as the outcome of the extraordinary change in the nature of the traffic which has taken place during the last fifteen or twenty years.

Changed Conditions.

The introduction of the safety bicycle resulted in very special attention being drawn to the condition of the surface of carriageways, which up to that time had been considered to be in a sufficiently good state of •repair for the then ordinary vehicular traffic. The later advent of the motor gave rise to still more serious problems in the preservation of a well-surfaoed carriageway free from dust, and the effect Of the high-speed traffic has involved the principle of highway safety which is the common right of the user. The principle of State control is recognised in some of the leading States of America' and in several Continental countries, but undoubtedly the best example is that which exists in France, where there are five classes or divisions of roads in respect of which (with the exception of the small local and parish roads) the Government takes a greater or lesser interest. The first division or "routes nationales," directly controlled by Government engineers under the Department of the Ponts et Chaussees, comprises a length of upwards of 20,000 miles.

French Compared with English Methods.

These national roads of France approximate in their length to the main roads of England and Wales, the total length of which, as referred to in the annual report of the Local Govern. ment Board for the year ended 31st March, 1906, is 27,380 miles. There are 53 county councils concerned in the upkeep of this length, and 825 urban authorities availed themselves of the right to maintain the portions passing through their districts, so that in all there were actually 880 maintenance authorities. The county roads are at present divided into two classes, viz., main roads and contributory roads ; the former, the county authorities either maintain, or, in the event of urban authorities maintaining, contribute the whole or greater part of the cost ; the latter are less important highways, the county authorities making an optional contribution towards the cost of maintenance, These contributory roads venulil rank with the second class of French roads (" routes departmentales") which are maintained at the joint cost of the Government and the communes

Assuming that a State department were to take over the control of certain roads, it does not necessarily follow that fEe whole of the above-mentioned 27,380 miles of county main roads would be transferred, as many routes which are accepted by the county authorities as main roads might not be regarded as national highways, but there may be certain main roads and contributory roads towards the upkeep of which a contribution might be made by the State, according to the degree in which such roads may be classed as through routes rather than Vocal roads. A State department would do away with the present control of the trunk roads by many authorities, and could more conveniently and satisfactorily deal with the maintenance, and the improvement and widening of the existing highways, as well as take into consideration and carry cut the construction of thos.e new trunk roads which, as a traffic necessity, will undoubtedly be required in the immediate future.

Advantages of State Control.

The advantages to be obtained by State control would be ; uniformity of practice in the work of construction and maintenance; a reduction in the cost, resultant upon the carrying out of the work in bulk instead of in sections ; and a fairer apportionment of the cost of maintenance and construction, as,

in principle, the national highways should be maintained au' of general taxation and not by local rate. Referring to the general principles in which the State could assist the work o highway maintenance, very valuable services could, without tht forming of an entirely new department or the disorganising 01 existing systems, be at once rendered in connection with tit( science of road-making materials, as touching the class 01 materials which should be used under given conditions. As far back as 18135, as the result of scientific investigation, table: were prepared in France for the guidance of road-makers it selecting their materials ; and, referring again to American prac. tioe, the Massachusetts IIighway Commission, appointed it 1893, governed by three commissioners, with duly appointed engineers, is advised by a geologist, and the same scientific advice is sought in other States.

The United States Department of Agriculture has rendered excellent service in the direction of research. For example, one of its most recent publications (January, 1907) gives the result of investigations as to the decomposition of felspars, and treats of the factors which mechanically, chemically, and physically modify that decomposition. Results are also given of the cementing values of mixtures of granites or diabases with lime. stones and dolomites, and the relative solubility of these mine. rals. Research work of this character is of the utmost value. The department also generally advises engineers in respect of materials that they propose to use for highway work. In this direction the method in England, while essentially practical, is non-scientific, and a great part of the acquired knowledge of experienced road-makers is unrecorded.

The Scope for Research.

There is much to be done, in the direction of research, which would materially assist in the more advantageous selection oi rocks for road construction and maintenance. Information is required as to the chemical and mineralogical composition of the rocks used, their structure, porosity, cleavage, crushing strength, resistance to abrasion, suitability for treatment by waterproofing material, and the possibilities of obtaining better results by the use in combination of different classes of material. An office of reference could preserve quarry samples and produce co-efficients of suitability for resistance to highway wear, with recorded notes of actual practice in macadam and all classes of permanent paving.

In connection with this subject, mention should be made of the valuable assistance which has already been rendered by the Geological Survey, and the interest which has been taken in the work of research by Mr. F. G. Ogilvie, C.13., principal assistant secretary for technology, etc., Board of Education, and by Dr. J. J. H. Teall, F.R.S., the director of the Geological Survey and Museum ; the names of Dr. J. S. Flett and Mr. J. Allen IIowe should also particularly be referred to. Under the auspices of the department a large number of rocks have been examined, and advice, within the limits of the research work already carried out, is given by the survey department to those applying for assistance in this direction ; but the system is far from complete, and is partly dependent upon private enterprise. Too much stress cannot be laid upon the necessity and desirability of the formation of a State highway laboratory, as it cannot be suggested that scientific research will do otherwise than materially assist in bringing about the best possible result in the construction and maintenance of the main and local highways of the country, and this phase of the question could be dealt with on its own merits and as distinct from the formation of a State road department. HOW FAR SKIDDING IS DUE TO ROAD SURFACES. Construction. and Materials. •

By DOUGLAS MACKENZIE, A.M.I.Mech.E.

The construction of roads from the point of view of the skidding to which self-propelled vehicles would be liable necessitates some study of the phenomena of skidding. Under normal conditions the wheels of the vehicle are supposed to roll over the road surface, the actual point or line of the periphery in contact with the road being quite stationary. Under such conditions the smoother the tire, and the smoother the road, the less would be the resistance to rolling action. This would be perfectly true if there were no forces acting on the wheel, but, in point of fact, there are numerous forces, and these are the cause of all the troubles in actual practice. With a wheel that is not driving the vehicle, there is the friction at the hub, which tends to prevent its rolling freely. The driving wheel, on the other hand, has forces exactly opposite trying to force the wheel round faster than the actual rolling, but, immediately the driving ceases, and the brakes are applied, exactly the reverse forces are acting. Again, the steering wheels have to resist the tendency of the vehicle to travel in a straight line, and there is a force tending to push these wheels sideways when they are turned through an angle. Lastly, there is the force of gravity, which is of no moment so Icing as it is at right-angles to the road surface, but is very important when the road surface is inclined. The existence of this force renders it necessary to obtain considerable adhesion between the tire of the wheel and the surface of the road, so that there shall be very great frictional resistance to any rubbing of the tire over the road surface as opposed to free rolling. This adhesion must not be obtained by any stickiness, which would prevent the tire from rising freely from the road as the wheel rolls forward ; it must be purely friction between the actual surfaces of contact.

The pneumatic tire introduces Some further problems, but it is not necessary to consider them separately. From the foregoing observations, it is clear that a finely-roughed surface is necessary to produce the required friction. Therefore, the primary necessity in selecting a material for a non-skidding road is to have a compound surface, composed of two or more substances, differing in the degree of hardness, but these materials must be so finely divided that the road is sufficiently smooth for perfectly free rolling. The co-efficient of friction on such compound surfaces is very high, amounting to as much as .8, but a further consideration of equal importance is that none of the substances of which the surface is composed should be able to form grease or a lubricating substance under the attrition of traffic. Granite is an ideal substance for this purpose, because it is composed of crystals of different materials differing in their degree of hardness, but it is impracticable to make roads of granite perfectly monolithic—that is to say, in complete slabs —the full width of the road. In order to make it practicable to construct a granite road, the material has to be divided into blocks of a sufficient size for convenient handling.

Some German Practices.

The most perfect granite surfaces are to be seen in Hamburg, where large setts are used, cut with extreme accuracy, so that the surface is perfectly fiat, and the joints are so small as to be practically indistinguishable. This is quite a different class of road to the granite-sett roads in our English towns, where the surfaces of the individual setts are very much rounded, and the tires of wheeled vehicles, instead of rolling smoothly, have to bounce from sett to sett. Granite roads made with perfect setts are almost noiseless, the only sound being clue to the hammer of horses' shoes, and, as this antiquated form of haulage is steadily reduced, the noise will be inappreciable. An approximation to this form of granite surface—and one that is very much cheaper—is that employed on many of the German country roads, and which is known there as " Klempflaster." It is introduced into this country under the title of " Cubette Paving" or " Durax Paving," and is composed of small setts laid at random, and broken by special machines to about 41-inch cubes. As the joints are none of them square to the direction of motion, the wheel is always riding on two or more of them, and does not jump from sett to sett. Consequently, the wear on these setts tends to smoothen the road instead of to roughen it as with common town setts.

Next to the first-class quality setts employed in Hamburg, the best surfaces are obtained by breaking granite to abont 14-inch cubes, and binding it by means of an elastic matrix. It is, however, necessary to remember that the thtet'SpaCeS between the pieces of broken granite should be very small, and, therefore, the 14-inch granite should be mixed with some 4-inch, some S-inch, and some granite dust, so that the quantity of matrix required is very small, and the joints between the pieces of granite in the road surface will never be more than 4-inch under the most adverse circumstances.

Waterproofed Roads.

There seems to be a great difficulty in getting tar to adhere to granite, and so the tar has to be treated by distillation, and also by the addition of various substances so as to alter its nature considerably. There are half-a-dozen such materials now on the market, and they will not only adhere to granite, but they are unaffected by English temperatures, and do not become soft in summer and brittle in winter as is the case with untreated tar. These materials give an exceedingly good surface from the non-skidding point of view, because, not only does one have the advantage of the compound nature of the granite. but one gets the addition of another substance of a different degree of harshness in a sufficiently fine state of subdivision to give the ideal roughened surface. It is also practicable with such a matrix to use limestone in a state of fine subdivision where limestone is much more easily obtained than granite, but this is not quite such a suitable substance, as finely-ground limestone has certain lubricating properties, and, therefore, the mud arising from this surface in wet weather makes a nasty slippery grease.

Great objection is raised by some councils to the cost of improved roads made on this system, especially for country roads, but it must be remembered that a great deal of the deterioration of country roads is due to the effect of weather instead of traffic, and, if a thoroughly waterproof road is constructed in the first instance, it is absolutely weatherproof, and, therefore, does not deteriorate from any other cause than the attrition of passing traffic.

How Much Camber?

I have already mentioned that one source of skidding is due to the action of gravity when the surfaces are inclined, and with a properly waterproof surface, the water will run off with much less camber than the old-fashioned roads. Probably a camber of 1 in 50 will be quite sufficient for these roads, and therefore the skidding due to the pull of gravity towards the gutter need not be at all a serious matter. The mistake has been made in some parts of the country of adopting waterproof roads with the same road contour as that previously in use, but one a the great advantages of modern materials is the reduction of the camber which they will permit.


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