THE MERITS OF A CONCAVE-SHAPED ROAD.
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Draining to the Centre Instead of to the Side ; the Removal of the Ditch and the Gullys Advocated as a Road Improvement.
By Alexander Cameron (late District Surveyor, Norfolk County Council).
ALMOST daily we are confronted in the columns of the Press with reports of motor accidents, all more or less serious, occurring on our rural county roads, and not always are these accidents the result of negligence, although this and inefficiency on the part of drivers of private cars are admittedly responsible in some instances.
Therefore it is perhaps not without cause that we sometimes wonder if everything humanly possible is being done by our road authorities to safeguard the road-using public and if anything further can be done to eliminate the risk of danger. More particularly when road accidents are of frequent occurrence we are impelled to wonder. if the road itself as at present constituted is altogether suited to present-day requirements.
Within recent years, it is true, speed limits have been fixed at certain places, warning signs erected and blind corners improved, whilst roads generally are being formed with less camber and the safety white line has been introduced at dangerous cross-roads.
Such improvements are all, no doubt, verb' desirable, . and legislation may still further assist from a theoretical point of view, but having regard to the ever-increaslug motor traffic on our public highways, it would appear that, without something of a practical nature in addition, the difficult and intricate problem of "Traffic and the Road" is not yet quite satisfactorily solved. In the interests of the public safety it must, sooner or later, be faced.
• Has Road Construction Advanced ?
Illustration No. 12 shows a transverse section of the average present-day rural county road which, in MY opinion, astonishing as it may appear, is very little different, save in top layer of bituminous material or reinforcement, from the Macadam and Telford road of nearly a century and a half ago, with US more or less camber, its open ditches, and its grips and outlets ; yet, with all due respect to road surveyors, whose job, doubtless, IS no sinecure, I sometimes think, if the modern road surface has been improved by the use of materials of a more adhesive and lasting nature, its foundation sometimes appears to be of inferior construction to that of Macadam's, wherein the ballast constituting the "bottoming" was invariablot graded and hand-set and not dumped "in situ," irrespective of uniformity of size and dependent on a steam roller to do the needful consolidating. Evidence of the employment of this latter modern method soon becomes apparent in the deterioration of surface, often erroneously attributed to the wear and tear of excessive and fast-going traffic, whereas it actually is not infrequently due to subsidence in a weak and badly prepared foundation.
The Advantages of Elevating the Roadsides.
Doubtless, and having regard to cost, many and varied are the opinions as to what should constitute the safe and up-to-date rural roadway. Personally, on the score of economy of upkeep and modern traffic efficiency, I am inclined to favour the road of flat crosssection or one as nearly fiat as possible, having regard to the need for providing quick surface-water drainage, which latter difficulty, however, has, since the fEtroduction of surface-tarring and the use of bituminous material as a top layer, been to a great extent overcome. With a surface of such shape, the maximum travelling width with the greatest possible safety is obtained, but whether the slight fall (perhaps about f, in. per ft. transversely) should be from centre to side or from side to centre is a debatable question.
A cross-section of a road of the latter shape is shown in ray third illustration, and much may be said in favour of the adoption of the shape shown; in certain cases, at least, if not for general use. Its maximum width of carriageway should, in my opinion, be not less than 22 ft., with a footpath formed on one side and, obviously, in the interest of the pedestrian, as far removed from the edge of the road as circumstances will admit.
For surface-water .hrainage the concave road is well adapted, as, with a single drain near the Ventre, it at once dispenses with the dangerous open ditch and grip or gully. On the "fall to centre" road the risk of skidding to the wrong side, with the prospect of a header into the open ditch, would be avoided, and on an embankment, for the same reason, the danger of a plunge into space would be considerably reduced.
Further, and as will be observed from the illustra tion giving a half cross-section, the ,greatest strength of this road is at its sides, where, in my opinion, it
ought to be if it is to resist, with the minimum of injury, the pressure of the heavy modern load. Then, again, traffic from opposite directions, rather than run in one common centre as on the cambered road, would have a tendency to hug its proper side, which would not only mean a comparative degree of safety, but would be a consideration in upkeep and maintenance of surface. At cross-roads, right-angled corners, acute bends and awkward turnings, a road so shaped would, I venture to suggest, be a decided improvement on the present one.
As is well known to motor drivers, weak and low side channels are often unsafe to drive over, the weakness sometimes extending from the grass verge outwards into the roadway to as much as two or three feet—a matter in-itself alone sufficient to justify some alteration or improvement. ' Therefore, whatever the shape of the road transversely, convex or concave, obviously strength at the sides is an important factor, and, perhaps, as necessary to the stability of the road as the foundation and scarcement are to the house. • The open ditch, still conspicuous •but a veritable death-trap, particularly on narrow thoroughfares, -should find no place on the up-to-date road, but should be removed to the field side of the fence, practicable in most cases, and where, for surface or subsoil drainage, it would answer its purpose equally well. Moreover, although frequently met with, it is not necessary on " hillset " roads. Nature does the drainage efficiently there—both subsoil and surface. In such cases, however, a sound water-table paved or surface-tarred is desirable. Neither should the telegraph pole find a place on the modern road, but should be removed to the field side, or dispensed with altogether in favour of the underground system. Grips and outlets, unless piped, are to be condemned ; the same remarks apply to excess of camber and over-high edges. Milestones placed near the carriageway are also a source of danger, are rarely noticed, seldom consulted, and, in most cases, might well be dispensed with, so far as the majority of the road-using public is concerned. Mileposts atbranch and cross-roads, of suitable height and easily discernible, would appear to a sufficient for modern requirements.
Dangerous hills might have their gradients indicated at the summit-1 in 4, 1 in 5, or 1 in 8, as the case may be, which would perhaps serve as a more effective warning than any danger-notice by letting the motor driver at once know what he is approaching; the question of danger would then rest entirely with himself to decide and he would drive accordingly.
Such, briefly, are a few points which have occurred to me as a result of close observation of the 'road" generally in its relation -to modern traffic, and I offer. themi in the hope that they may prcive'intereing, and • even instructive_ The fact remains, and is becoming more apparent every day, that our rural county highways call for still further improvement, and so long as they remain unnationalized it is up to road authorities to give the fullest consideration to any suggestion which has for its objects the public safety and the reduction of the ever-increasing "toll of the road."