The Improvement and Maintenance of High.
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ways to Meet Modern Traffic Conditions.*
By JOHN S. BRODIE, M.Inst.C.E., Borough Engineer, Blackpool.
The mileage of public highways in the -United Kingdom is approximately as follows:— At the low estimate of £1000 per mile for an average width of 18 ft. of carriageway, and £500 per mile for bridges, cuttings, and embankments, our highways cannot have cost us less than 350 millions sterling.
ow, considering that by far the larger proportion of -our highways were made about the beginning of the last century, when the traffic conditions for which the roads were made were totally different from what they are now, and also keeping in mind that the moderate traffic then using the highways practically disappeared for three-quarters of a century in consequence of railway dompetition, it is not to be wondered that our highways have been much neglected, and a valuable national asset suffered to fall into a very bad state of repair.
Then came what we may call the "road revival" with the traction engine, the light road locomotive, the bicycle, and the light and heavy motorcars, with their steel tires; solid rubber and pneumatic tyres, and loads of from 12 to 20 tons on two axles.
The result has been what might have been expected, and as if modern railway locomotives and trains had been suddenly run on the original rails laid down by George Stephenson on the old Stockton and Darlington Railway.
The problem which now faces those of us who are responsible for the state of our highways is indeed a formidable one. The President of this Institution, in giving evidence before a Commission on heavy motor traffic, stated as his considered opinion that a sum of 257 millions sterling would require to be spent on the roads of this country to enable them to meet successfully the new traffic conditions. The author considers this estimate from so eminent and experienced an authority to be well within the mark and perfectly reliable.
In this short paper the author proposes to discuss the subject of urban and sub-urban roads, leaving the question of county and rural roads in the able and experienced hands of his friend Mr. Gettings, the county surveyor of Worcester.
Road I mur ove me Ms .
The improvements of existing highways may be conveniently considered under the following headings (a) Foundations and wearing surfaces. (b) Widenings. (r) Diversions.
(d) Gradients.
(e) Corners and road junctions.
(f) Cutting hedges and trees.
(a) Foundation and Wearing Surfaces.
It has frequently appeared from discussions on this subject in the Press, and even at conferences of road engineers and road users such as the last Inter
national Road Congress, that there were no settled questions in regard to road foundations and surfaces. The author considers that this view cannot be seriously maintained, but that, on the contrary, we have agreed on points like the following :— 1. That all roads, whatever the amount of traffic may be upon them, must be properly drained, and must have adequate foundations, either of hand-pitched rubble or Portland cement concrete.
2. That the strength of the foundation must be fixed in relation to the amount of traffic it is likely to carry.
3. That wearing surfaces must bear a proper relation not only to the amount, but also to the nature of the anticipated traffic.
4. That water-bound macadam under modern traffic conditions is unsatisfactory from any point of view.
5. That the use of any and every " local " stone for road making or mending solely on the score of cheapness of first cost is financially unsound, and that only suitable material for roadmaking should he used.
6. That to make or maintain a road above or below the requirements of its traffic conditions is equally unsound financially.
(b) Widenings.
It has recently been laid down by a high authority that, except in the immediate vicinity of towns, a metalled width of 18 ft. of carriageway is generally adequate for traffic purposes. Now, in urban or sub-urban areas, an 18 ft. width of carriageway between kerbs is absolutely inadequate. The author's own practice is a minimum of
32 ft. 6 ins, between kerbs for roads upon which there is any possibility of through traffic, and a minimum of 21 ft. for what may be considered merely as roads for access to residential property. The width of 32 ft. 6 ins, allows for a possible double line of tramways to Board of Trade requirements, and also for width of heavy motorcars under Local Government Board regulations—two very important advantages. Larger widths are, of course, necessary for greater volumes of traffic; the ideal width_ providing for (a) two standing vehicles one on each side of the carriageway and immediately opposite each other ; (b) two lines of slow traffic ; and (c) two lines of fast traffic; or a total width between kerbs of 54 ft.
Road-widening improvements in built-up areas must always be very costly. Some interesting figures have recently been collected by Mr. W. T. Lancashire, city engineer of Leeds, arid published by him, in regard to eight of the largest English towns, exclusive of the Metropolis? who have collectively spent over 16i millions sterling on road widening at an average cost of nearly is. in the 2 on their rates.
The obvious moral is, therefore, that road widenings should be made (and made on a liberal scale) well in advance of building operations, when the cost will be quite insignificant and the future benefits very• great.
(e) Diversions.
Road diversions are generally made (a) in order to shorten the road or (b) to avoid excessive gradients by making a detour. In both cases the diversions can often be shown to be justified on grounds of economy alone. In a proposed diversion of a main road partly within (but chiefly outside) the author's district, the length of the present road is 2 miles 80 lineal yards, while the length of the road when diverted in a nearly straight line will be i mile S furlongs 113 yards. It will thus be shortened by 627 lineal yards, or less than 83 per cent, of the present length. The gradients will be considerably improved in the new road, so that the annual saving in maintenance will be upwards of 17 per cent., which will be a very good return on the capital outlay for carrying out the scheme, and a permanent saving both as regards maintenance and use for all time.
On the other hand, the author has made diversions where the horizontal length has been increased, but the reduction of gradient has been so considerable that both in regard to the user and also the cost of maintenance the advantages of the diversion have been amply proved.
(d) Easier Gradients.
The author considers there will be general agreement as to the three classes of ruling gradients in urban roads, viz. : For fast traffic not exceeding 1 in 50. For mixed traffic, not exceeding 1 in 30.
For purely local traffic, not exceeding 1 in 20.
In hilly districts, however, it will often be impracticable to obtain gradients even distantly approaching those given above.
A few years ago Mr. Howard-Smith contributed a few interesting statistics as to road gradients in towns, and their paved surfaces, over which very heavy town traffic passed. These gradients, in addition to their steepness, were of considerable length, as follows :— (e) Curves at Corners, Crossings and Junctions.
At all corners or turnings the curves should not be less than 100 ft. radius, and the convex side of the road having solid fence walla or close hedges should be removed and replaced with open railing, so as to be as free as possible from obstructions to sight for at least 100 ft. forward.
Road junctions and cross roads should be properly bell-mouthed, when both &des of the road will, of course, be convex, and the same remarks apply.
Super-elevation, while it may be successfully adopted in simple turnings, should not be used at all in junctions or cross roads, but the cross road or junction should "mitre" into the main road, so as to avoid all "bumping" of fast traffic in both of the roads crossing each other. Secondary roads joining or crossing main roads should have warning or cautionary notices fixed, to slow down, as fast traffic on main roads should always have precedence over traffic on secondary or district roads.
(1) Cutting Hedges and Trees.
However picturesque they may appear, nothing will cause more harm to carriageway surfaces than overgrown and overhanging hedges and trees, which, by excluding the sun and wind from the surface of the road, prevent its being kept clean and dry. Fledges should be kept down by trimming at the proper time of the year, so as not to exceed 4 ft in height above the surface of the road, except at turnings, crossings and junctions, where, as already stated, they should be replaced by open fencing.
Road Maintenance.
The author must reiterate what he has often said before—that the most important factor in successful road maintenance is a staff of properly-trained workmen, and especially reliable foremen, and also that such well-trained foremen and workmen should be adequately remunerated, proportionate to the experience and skill required for the work entrusted to them. No other outlay in connection with road work will make such a handsome return as a sufficient and well-trained, well-organized and well-paid staff of workmen.
Then, only materials of the best quality should be used, both iii construction, repairs and renewals. A frequent cause of excessive costs in road renewals and repairs is due to the use of local material of low first cost, .but which turns out to be terribly expensive in the long run. The temptation to use unanitable material for road work because of its apparent " cheapness " should always be resisted. It is also of supreme importance that any signs of weakness in any part of the road surface, should be at once investigated, the cause of it clearly ascertained, the proper remedy applied and repairs effected without delay. It is further of importance, not merely for the sake of good sanitation, but primarily in the interests of the road itself, that all dirt and filth should be cleansed from the road before it has time to be trodden in by the traffic. The author inserts herewith in a tabulated form the cost of maintenance of all the roads in the ansa for which he has been and is the responsible engineer.
It will be seen from this table that although the mileage of the roads has increased during the last In years by about 17 per cent., the annual cost of maintenance has decreased about 32 per cent., the cost per mile showing a decrease of about 42 per cent. The author attributes this gratifying result entirely to the foresight of his authority, firstly, by insisting on all new roads being made on those principle a which experience has shown to be the best ; and secondly, in providing funds for practically reconstructing all existing roads so as to make them sufficient to meet all reasonable modern traffic conditions.