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According to the inclinations of a road, and the form and wetness of the country through which it passes, cross drains of good masonry should be built beneath it, having their extremities carried under the road fences.
One of these drains should be made wherever the water would lie on one side of the road, and can only be got rid of by carrying it to the other side. When the road passes along the slope of a hill or mountain, a great number of these drains are necessary to carry off the water that collects in the channel on the side next the high ground. They should be placed at from 50 to 100 yards' distance from each other, according to the declivity of the hill; so that the side channels may not be cut by carrying water too far. In these situations inlets should be built of masonry, to carry the water from the side channel into the cross drains. The manner of building an inlet will be described in the chapter on Road Masonry. On flat ground numerous outlets should also be made from the side channels, under the footpaths, or wastes and fences, into the field ditches.
In mountainous countries, where the road passes along slopes, it is necessary to carry open or catchwater drains, branching from the upper ends of the cross drains, in an inclined direction, so as to catch the surface water before it can reach the road.
After all these precautions have been taken, the preservation of the surface from injury by water should be further secured, by giving a proper con
vexity in the cross section, and by making regular side channels.
These side channels will be formed by the angle where the curved surface of the road abuts on the footpath, or other defining boundary of the roadway. They will be capable of carrying off a great quantity of water, without being made in the form of a square-sided drain.
Attention in making the surface of a proper convex form is particularly necessary on hills, in order that the water may have a tendency to fall from the centre to the sides, in place of running from the sides to the middle of the road, which it certainly will do unless the side channels are kept below the centre, in the manner hereafter described.
On all hills the greatest care should also be taken to keep the side channels always open; for, if they are obstructed with weeds or mud, the water will find its way over the middle of the road. The side channels should be all thoroughly repaired as well as all the drains before the approach of winter, and again after the winter is over; but, besides these repairs at fixed periods, daily attention should be given to take care that no obstruction takes place.
Whenever a branch or field road joins a main road, it should not be allowed to interfere with the side channel: in order to secure this object, the point of junction should always be on the field side of the side channel; unless this is the case, the branch or field road will, when on a higher level than the main road, carry its surface water upon the main road.
In addition to all these means recommended to be adopted for securing the drainage of a road, it is of the utmost importance that evaporation should have full effect in drying up the surface, by allowing the sun and wind to act upon it in the freest manner.
The necessity of giving a road a good exposure has already been mentioned under the head of "Laying out a Roadand the value of a rapid evaporation will be more fully explained when the repair of roads is brought under consideration.
Roads kept dry will be maintained in a good state with proportionally less expense. It has been well observed, that the statuary cannot saw his marble, nor the lapidary cut his jewels, without the assistance of the powder of the specific materials on which he is acting: this, when combined with water, produces sufficient attrition to accomplish his purpose.
A similar effect is produced on roads, since the reduced particles of the materials, when wet, assist the wheels in rapidly grinding down the surface.
A more particular description of the mode of constructing the several drains which have been mentioned will be given in the chapter on Road Masonry.
DIFFERENT KINDS OF ROADS, AND MODES OF CONSTRUCTING THEM.
There is not to be found in any of the books on road-making a distinction between roads for great and roads for little traffic. Each author has written as if there ought to be only one kind of road for every kind of use. This is a great mistake, and has led to much confusion in forming opinions upon the proper construction of roads. A road of earth, put into a regular form, will answer for a park drive. The same with a coating of gravel will do for light carts and other carriages. So a road made with ten or twelve inches of broken stones laid on the natural soil, will be a sufficiently good road when the traffic is not considerable; while very great traffic requires a road to be constructed in a different manner, that is, with much greater solidity and hardness, so as to allow carriages to be drawn on it with the smallest possible quantity of tractive power, the object that all road-makers ought to have in view.
The different kinds of roads may be distinguished and described as follows:—
1st. Iron railways.
2d. Paved roads.
3d. Roads of which the surface is partly paved and partly made with broken stones or other materials.
4th. Roads with a foundation of pavement and a surface of broken stones.
5th. Roads with a foundation of rubble stones, and a surface of broken stones or gravel.
6th. Roads made with broken stones laid on the natural soil.
7th. Roads made with gravel laid on the natural soil.
The uses and advantages of iron railways with locomotive engines have of late been so fully explained in several works of great ability that it is not necessary to repeat in this what was stated respecting them in the last edition.
The eagerness which was so generally displayed by vast numbers of persons to give credit to the representations of the great profits to be realized by railway shares, gave so much encouragement to all those adventurers, who looked to derive immediate advantage from railway projects, that acts of parliament have been passed for railways in every part of the kingdom. The experience, however, which has been gained from those already completed, and from the enormous expense incurred on those which are in progress, has led to a general opinion that there is little probability of more than a few of these works affording any ultimate return for the money expended upon them.