ROADS
SOME POINTS AFFECTING THE SPORTING MOTORIST
T0 those engaged in the construction of roads, it is a matter of no small wonder that so little attention has been given to this subject in our motoring journals. Without the rapid improvements in highways, carried out during the past dozen years or so, it would have been impossible for the tremendous growth in motoring as a whole, and in sporting motoring in particular, to have taken place.
In the case of a railway, that part of the system which is of the greatest importance, and which receives the greatest amount of attention, is the ” permanent way.” The type of train, the speed at which journeys can be accomplished, and the comfort in travelling are all dependent on the design of the ” permanent way.” The motorist’s “permanent way” is the road, and his ability to perform fast, safe journeys upon it is the result of careful research on the part of those responsible for the design and construction.
Recent Improvements.
Most of us remember the dreadful state in which our roads were left after four years of neglect during the War. Broken springs were the rule of the day, clouds of dust followed each car, and a journey of any duration was in most cases a matter of discomfort. The position was aggravated by the fact that the motor industry had turned its attention to the production of cars on an unprecedented scale, and it was obvious that drastic methods would have to be resorted to, in order not only to make the roads fit for the use of the then existing traffic, but for an enormously increased volume of road users and for loads and speeds hitherto unthought of. In order to meet this urgent necessity, the Ministry of Transport formulated a comprehensive programme of road construction and improvement throughout the whole country. Most of the money needed for these schemes was raised by means of a newly imposed tax on motor vehicles. At the By E. WINGROVE KEER,
A.M.I.C.E.
same time the problem of unemployment occupied a prominent position in the affairs of the day, and it was planned partly to counter this by drafting the unemployed on to large road construction works. This particular class of work was known as “Relief Work.” The projects were planned, let out to contract, and supervised by the Ministry of Transport or local government bodies.
Many of our new arterial roads were commenced during this period ; some were successful, others were partial failures due to lack of experience, or through provision for the rapidly increasing weights to be borne by the road not having been made, but mostly they were successful. Examples of these earlier arterial roads are the new Southend Road, the Dartford By-pass and Watling Street, the Great West Road, the Croydon By-pass, the Barnet and Watford By-passes, the Birmingham-Coventry Road, and many others.
Important and necessary as these fine new roads are, it is mainly the numerous small improvements in all the main roads and subsidiary roads, carried out during the last ten years or so, that have been responsible for providing motorists with the excellent means for rapid transit that they now enjoy. It is to be hoped that the fervour for economy, about which we now hear so much, will not result in another period of such neglect as to cause damage to our highways that would be irreparable without colossal expenditure. Like machines, roads need maintaining, and without this necessary maintenance, although for a time they may carry out their duties, it means a heavier repair bill in the end ; and from the motorist’s point of view this preiod of neglect would be deprecated through reason of the declining efficiency of their medium of travel.
There are many and varied points to be taken into consideration by the engineer when he is planning the construction of a new road, or the improvement of an old one. The latter proposition is usually the more difficult, for then he often has problems to deal with involving an alteration to, or even in some cases the demolition of, buildings adjacent to the highway. These are the cause of considerable complications, and, in fact, sometimes determine the alignment of the reconstructed roadway. That part of the road with which the motorist is principally concerned is the actual surface of the carriageway, but this happens to be the last point of consideration of the road builder. The re-surfacing of a road is a simple matter compared with an alteration, however small, to the actual limits of the highway as a whole. For instance, the easing of a dangerous bend might involve the preparation of quite a number of plans, and a not inconsiderable amount of litigation before the work can proceed. As often as not, a house or some other building is situated near the scene of operations and will be affected by the contemplated improvement.
Planning a new road.
When an entirely new road is to be constructed, a tentative location is first drawn out on the Ordnance Survey sheets ; this is then checked by a preliminary surveying on the site, and a definite position finally arrived at. A more exact survey is then carried out, and on large scale plans prepared from this the new road is plotted and every detail of the construction schemed out. These plans become the working drawings from which the road is actually built. Where the new highway passes over undulating ground, as is usually the case, it is necessary that the gradients are not excessive, and In order to effect this, cuttings and embankments are formed. As far as possible, the engineer arranges these so that the amount of excavation will be equal to the amount of embankments, otherwise should
his embankments be in excess, it will be necessary to excavate, unnecessarily, material to make up this excess. On the other hand, if there were more cuttings, then some means of disposal of the material not required for embankments would have to be found. This is termed a spoil bank and is avoided as much as possible, because it often means hauling the material some considerable distance. Diagram 1 illustrates how the balance of cuttings and embankments is arrived at. In hilly country the earthworks, as the excavation and filling is termed, is a serious item of expenditure in the construction, and great care is taken to ensure its being a minimum. Nowadays, mechanical excavators are used extensively, and thereby costs have been reduced considerably. These are now mostly driven by oil engines in place of steam, and are mounted on caterpillars, by the use of which the machine is considerably more mobile and the necessity for an expensive railway track obviated.
Embankments.
A mechanical excavator will scoop out a ton of earth and load it into small tipwaggons. These tip-waggons, in sets of about a dozen, are hauled by steam or petrol locomotives to the site of an embankment, where their contents are tipped until the ground is raised to the desired level. In practice the embankment is made up to a higher level than will be eventually required this extra height allows for the subsidence which naturally takes place. This settling of an embankment is one of the most difficult problems with which the road engineer has to contend. During the first year the ground rapidly sinks ; thereafter the process continues, but to a lessening degree, for several years. For this reason if possible, embankments are left to stand for about a year before the actual roadway is formed upon them, and even then the general policy is to lay what is termed a temporary surfacing. This is probably of a more flexible nature than that on the other more stable parts of the road, and is intended to last for a short time only, while, in fact, the greater part of the settlement of the bank is taking place.
When the tipped material has become sufficiently consolidated, permanent foundations and surfacing are constructed. Readers will probably have noticed work of this nature being carried out on roads with which they have been familiar for a number of years.
Temporary Surfacing.
Whilst the temporary surfacing is carrying traffic, the negotiation of that part of the road is generally a somewhat uncomfortable one for motorists, and there are often complaints regarding the irregularities of the carriageway, but, as will be readily appreciated by the foregoing remarks, this period of transition from an unstable to a stable condition cannot be avoided. A usual type of temporary carriageway takes the form of a foundation consisting of hardcore (i.e. broken bricks, broken lumps of old concrete, stone, slag, etc.) and a surfacing of tarxnacadam. A foundation and surface so constructed are of such a nature as to stand a good deal of flexing without an actual break-up of the carriageway. Were we to adopt concrete or some other equally rigid form of construction, it is obvious that any settlement of the ground beneath would cause a complete fracture, which would result eventually in a complete collapse of the material.
Road Foundations.
That part of the roadway which in cuttings lies between the toe of the slopes, or on embankments between the top of the slopes, is referred to as the formation. The formation width generally adopted for a modern road is 60ft., and is made up of a 30ft. carriageway divided from two footpaths on either side by grass -verges. Diagram 2 illustrates a typical road formation. Various methods are adopted for the construction of the foundation to the carriageway, and to some extent will depend upon the surface to be used. The pitched foundation consists of large pieces of stone set edge-ways upon a layer of ashes, the whole being eventually rolled and blinded in with smaller material. A cheaper form of construction and one which is almost as good is made up of hardcore, consolidated on a bed of cinders.
Nowadays, however, the trend is towards the reinforced concrete foundation, which has the great advantage of being able to span localised soft places in the ground and provide a rigid base upon which to lay the actual road surface, unless it is decided, as is often the case, to utilise the concrete itself as the road surface.
Concrete, like all other materials, expands with heat, and, as on a railway gaps are left between each length of rail to allow for expansion, so in the concrete road allowance for movement, under the influence of heat, must be made. This is arranged for at regular intervals by a joint about inch in thickness, which runs across the full width of the road, and which is filled with a bituminous substance easily compressed. Without such an arrangement, in very hot weather the concrete would rise up and crack in various spots. The thickness of a concrete foundation varies ; where it is intended to lay upon it a surfacing material, 6 inches is usually adopted, but if the concrete is to act as a wearing surface 8 inches or more is laid ; for in this case the cushioning effect of a surfacing medium will be absent.
Concrete Roads.
The majority of concrete roads are reinforced with some form of steel mesh which serves several purposes. It binds the whole together in a homogeneous mass, assists the concrete in bridging soft places in the subsoil, and prevents irregular cracking due to climatic changes. This reinforcement usually takes the form of a number of steel bars about a quarter of an inch in diameter, welded together to form a kind of mat, and is supplied in rolls, but there are many other varieties, although they serve the same purpose. Years ago concrete, which consists of stone, sand and cement mixed with water, was made by hand, the ingredients being dumped on a board and turned over with shovels. Needless to say this method of manufacture is of necessity slow, and the cost of constructing a concrete road by such means would be prohibitive. Machine mixing has replaced the old-fashioned hand-mixing, and with the same number of men ten times as much material can be
laid, The ingredients, in the correct proportions, are tipped dry into a hopper behind the machine which is elevated by power till its contents are emptied into a revolving drum. Water is added, and after a space of one minute the mixture is delivered from the drum ready for laying, the whole process taking but a few minutes. An important point which the road builder must watch in laying a concrete road is the finishing of the surface. Great care has to be taken to see that no undulations occur, and in order to effect this before the concrete is placed, rigid edgings of timber or steel known as screeds are set up, so that their top edges are exactly coincident with the finished surface of the road. The concrete is laid and brought to the correct level by what is known as tamping. This is done by means of a plank on edge, which is worked along the top edge of the screed, and at the same time bumped up and down. The plank is iron shod on the working edge and is provided with handles at either end, by means of which it is lifted. In the United States mechanical tampers are in use, but in this country they have not become general practice.
Concrete as a surfacing medium has the great advantage that it is never slippery in any kind of weather. Most other road surfaces need periodical treatment to render them non-skid. Some motorists have complained that concrete results in heavy tyre wear, but it is apparent that one cannot have it both ways ; if a nonskid surface is required this means tyre grip, and tyre grip obviously results in tyre wear. From the point of view of speed, which to us racing enthusiasts is a matter of principal concern, the material which causes the least amount of friction, and upon which a car is most lively, is asphalt.
Asphalt, Tarmacadam, etc.
Amongst the general public there is a good deal of confusion as to the difference between asphalt, bituminous macadam, and tartnacadam. The term asphalt, strictly speaking, describes the material found in the natural asphalt deposits of Switzerland, Trinidad and elsewhere, but of late it has been used to describe practically any kind of road paving having a
matrix, or binding agent of natural asphalt or bitumen. Bitumen is extensively, manufactured from the residue of crude oil after the distillation of the lighter oils has been effected. Rock asphalt, with which many miles of London streets are paved, consists of limestone naturally impregnated with bitumen and is mined from deposits found principally in Switzerland. It is crushed into a powder and heated before being laid. The powder is spread and consolidated by punning, which has the effect of forming it into a rocklike substance again. This form of paving is used generally on streets carrying very heavy traffic. A similar form of asphalt is known as mastic and is manufactured by “
cooking” limestone and bitumen till the former is thoroughly impregnated. The mixture is spread in liquid form and brought to an even surface by hand with floats.
The most usual form of asphalt nowadays, however, is what is known as steam rolled asphalt. This is manufactured by heating and drying aggregate consisting of stone and sand to which is added hot liquid bitumen, the whole being thoroughly mixed together in a special machine. The mixture is then transported to the road, spread by raking, and finally rolled by steam roller, the whole process taking place whilst the material is still hot. When cold, a hard impregnable surface is the result. There are numerous other types of asphalt which are variations of the above, but broadly speaking the three classes described may be taken to encompass asphalt pavings. Owing to their tough, compact nature surfacing mediums of this kind are popular with both sporting motorist and road engineer. They appeal to the former because of their smooth, fast finish representing the minimum of friction between tyre and road, and they find favour in the eyes of those responsible for the upkeep of our highways, by reason of their long life. It is usual to require layers of asphalt to guarantee their work for a period of five years or even longer, and this they are willing to do without hesitation. We now pass on to a consideration of
another class of ro-d surfacing, viz., tarmacadam. This has for many years constituted the most popular method of paving our roads, and has given eminently satisfactory results. It consists of broken stone, slag, flints or other hard material coated with tar. In the process of manufacture, which is usually carried out at the site where the aggregate is found, the stone is thoroughly dried by passing it through a heated revolving drum, and. then mixed with the correct proportion of tar which has been previously reduced to a thin consistency by heating in boilers. Unlike asphalt the mixture is laid cold, and therefore possesses the advantage of being able to be stored for an indefinite period before being laid. During laying operations the material is delivered to the road where it is spread with forks to the required thickness, and consolidated by means of a steam roller. Due to the fact that the binding agent is tar, which always remains in a liquid though viscuous state, tarmacadarn is of a comparatively flexible nature, and can in consequence be laid on more or less inferior foundations without serious trouble developing ; but this flexibility is often the cause of complications in hot weather. It becomes semi-plastic with a liability to be pushed into corrugations and deformations by the traffic, and these will set firm and be perpetuated when cooler climatic conditions follow. This deficiency has been overcome to a large extent by adding a small percentage of bitumen to the tar during the process of manufacture, and most tarmacadam laid nowadays is so treated. When laid on main roads tarmacadam is usually dressed every year with a tar or bituminous compound. This is heated till it assumes a thin liquid form, and is sprayed on to the road surface from a special machine. Chippings are then spread and rolled in. Asphalt is sometimes treated in this way too, but the latest practice adopted for rendering the latter entirely skid-proof is by rolling chippings, which have been previously coated with bitumen, into the surface whilst the material is still warm. The road pavior has a very difficult problem with which to deal. His material must possess a surface when laid that
provides a sufficient amount of tyre grip to ensure its being non-skid ; at the same time the surface must be entirely impervious to moisture, and be devoid of crevices or holes in which water could reside, where, in the winter months, it would freeze and crack up the paving material. To satisfy both these conditions at the same time it is no easy matter. However, the enormous improvement in -our highways during the past few years testifies to the fact that the difficulty has been largely countered by the ingenuity of the road pavior.
Surface Dressing of Carriageways.
From the experience gained in the use of tarmacadam and asphalt, a host of other surfacing materials has been evolved. Generally these take the form of something between the two and aim at securing some of the advantages of pukka asphalt at less cost. A recent innovation is cold laid asphalt, but this is still more or less in the experimental stages, and up to the present has not given such universally satisfactory results as the older established processes. In this case the matrix is formed of bitumen which has been rendered temporarily liquid by an emulsification, or by the addition of a fluxing agent. In either case the principle is the same and relies upon the evaporation of the lighter ingredient after the material is laid, leaving behind the more solid
bitumen as the binding agent.
The seasonal surface dressing of roads is now general practice, and many thousands of miles are so treated every year. Most of the second-class roads consist of old water-bound macadam, which after many years of dressing is almost equal to tarmacadam. To ensure that the work of surface dressing is effective it is necessary to carry it .out when the roads are perfectly dry. For this reason it is done mostly in the spring or early summer. Many motorists are justifiably annoyed at what they call ” the tarring “of the roads, and every year vigorous protests are raised against it. As a matter of fact, the evil is largely exaggerated in most cases, for nowadays the tendency is to use quick drying bituminous compounds over which a liberal coating of chippings is rolled in. It is possible that in the future the application of a surface dressing may be carried out with less annoyance to motorists, but it is obvious that to do such work, whilst maintaining a way for traffic, without causing inconvenience, is an impossibility. We must remember that the practice of annual dressings saves the rate payer incalculable sums of money by holding together road surfaces which would otherwise break up during the winter months.
Wood Block Paving.
A type of road surface not yet mentioned, and with which we are all familiar, is wood block paving. For heavily trafficed urban centres this has proved eminently mutable. The first cost is high, but this is justified by the extremely long life enjoyed by a pavement of this type. A very stable foundation is needed upon which to lay the blocks, and consists of a liberal thickness of concrete. Wood blocks
possess the advantage of quietness and freedom from the possibility of development of corrugations, a feature not enjoyed by either asphalt or tarmacarlam. Considerable trouble used to be experienced by reason of the liability of the blocks to swell and heave up in patches after heavy rain. This inconvenient characteristic has, however, of late been overcome by an ingenious device which provides a space for expansion between each block, and yet at the same time holds them firmly in position.
Drainage.
The drainage of the carriageway is an important item, and the success of a road is often dependent on whether or not this has been given the careful consideration due to it. If water is allowed to stand in places a disintegration of the surface will often follow, and from the road users’ point af view nothing is more unpleasant than when a deluge of water follows every car, sending showers of spray on to the wind-screen of the motorist behind and
over pedestrians on the side-walks. On most of our roads, surface water is dealt with by cutting troughs, or grips as they are termed, through the grass verge and leading water into ditches running alongside the hedges. These act principally as soakaways, but any excess water is fed into streams, rivers, etc. Occasionally there are no ditches, and the water is led through the highway boundary on to the adjacent land, where it soaks away. Whenever roads are reconstructed, these old fashioned and often inadequate methods are replaced by a proper system of drainage. Gullies are placed at regular intervals and at all low spots, and into these the water flowing along the channels of the carriageway is led through the familiar gratings. The gullies empty into a drain running along the roadside under the grass verge, and this in its turn is led to a stream or other convenient spot for disposing of the water. In some cases• underground soakaway pits are constructed.
A host of incidental works confront the road builder, besides those items we have briefly surveyed. Several bridges may be required on the stretch of road to be constructed or improved, and retaining-walls, boundary fences, culverts, road junctions, and many other odds and ends may call for more consideration and the exercise of more ingenuity than the road proper.
Road Curves.
Now a few words, before closing, on road curves. In all new work curves on roads are radially correct, that is to say they are true portions of circles of given radius. Naturally a curve of the largest possible radius • is adopted, except in certain cases where it is desirable, for the sake of visibility, to keep the carriageway on the outer edge of the formation width. In modern practice on all curves below a radius of about two thousand feet the carriageway is super-elevated, or to use a term more familiar to motor racing enthusiasts, is “banked.” Up to the present the tendency has been to give roads an insufficient amount of superelevation, but one must not forget that
until two years ago the maximum legal speed for cars was 20 m.p.h., and authorities did not consider that they were entitled to cater for speeds of 40 or 50 m.p.h. There is no doubt that the future tendency will be towards more super-elevation at curves, The super-elevation of bends is a very important contributory factor to the elimination of accidents, for the following reasons : (1) it counters the tendency of the car, through centrifugal force, to skid across the surface ; (2) by reason of the fact that it is just as easy to negotiate super-elevated bends on the outside as on the inside, the tendency to cut corners by motorists will, when they realise the truth of this, be less prevalent ; and (3) the super-elevation of the road actually turns the wheels of the car in the right direction. Some people have suggested that transition curves should be adopted in laying out roads. A transition curve, as the name suggests, is a method of gradually leading up to a curve of given radius
instead of at once swinging away from the straight. Diagram 3 illustrates this. • The writer does not agree with this suggestion. Those who drive sporting cars will be familiar with that unpleasant type of bend which, when they first turn into it, appears to be comfortably negotiable at forty miles an hour, and then unexpectedly sharpens up to something demanding a much slower speed. This necessitates sudden braking whilst turning, which everybody will agree is an undesirable feature. On these occasions the motorist has encountered what is in effect a transition curve. As a matter of fact the safest kind of bend would be one which is the reverse of a transition curve, where the radius after the first few yards would be constantly increasing. Were all our roads one-way routes this would be possible, but obviously could not be arranged for two-way traffic.
Motor Ways and a New Racing Road Circuit.
In conclusion one cannot refrain from expressing the hope that one day this country will follow the example set by
several of the continental countries in constructing Motor Ways, or” Auto Stradas.” The late Lord Montague of Beaulieu was actively interested in several schemes of a similar nature in our own land, including
a privately owned Motor Way between London and Birmingham, and another leading to the South Coast. The foutes were surveyed and the plans drawn, and at Olympia in the Autumn of 1923 models of proposed road junctions were exhibited, but the schemes, though admirably planned in every detail, have failed to mature. Such institutions would provide an interesting trial ground for owners of sports cars. However, they may console themselves in the thought that before many months have elapsed they will have at their disposal, only thirty miles from London and within easy reach of all Midland towns, a really first-class motor road circuit having a perfect concrete surface and real mountain climb, where they will be able to indulge in thrilling tests and speed bouts to their heart’s content.