The grade is the most important factor to be considered in the location of roads. The smoother the road surface, the less the grade should be.
Whether the road be constructed of earth, stone, or gravel, steep grades should always be avoided if possible. They become covered at times with coatings of ice or slippery soil, making them very difficult to ascend with loaded vehicles, as well as dangerous to descend. They allow water to rush down at such a rate as to wash great gaps alongside or to carry the surfacing material away. As the grade increases in steepness either the load has to be diminished in proportion or more horses or power attached. From Gillespie we find that if a horse can draw on a level one thousand pounds, on a rise of—
| 1 foot in— | Pounds |
| 100 feet he draws | 900 |
| 50 feet | 810 |
| 44 feet | 750 |
| 40 feet | 720 |
| 30 feet | 640 |
| 25 feet | 540 |
| 24feet | 500 |
| 20 feet | 400 |
| 10 feet | 250 |
It is therefore seen that when the grades are 1 foot in 44 feet, or 120 feet to the mile, a horse can draw only three-fourths as much as he can on a level; where the grade is 1 foot in 24 feet, or 220 feet to the mile, he can draw only one-half as much, and on a ten per cent grade, or 520 feet to the mile, he is able to draw only one-fourth as much as on a level road.
As a chain is no stronger than its weakest link, just so the greatest load which can be hauled over a road is the load which can be hauled through the deepest mud hole or up the steepest hill on that road. The cost of haulage is, therefore, necessarily increased in proportion to the roughness of the surface or steepness of the grade. It costs one and one-half times as much to haul over a road having a five per cent grade and three times as much over one having a ten per cent grade as on a level road. As a perfectly level road can seldom be had, it is well to know the steepest allowable grade. If the hill be one of great length, it is sometimes best to have the lowest part steepest, upon which the horse is capable of exerting his full strength, and to make the slope more gentle toward the summit, to correspond with the continually decreasing strength of the fatigued animal.
So far as descent is concerned, a road should not be so steep that the wagons and carriages cannot be drawn down it with perfect ease and safety. Sir Henry Parnell considered that when the grade was no greater than one foot in thirty-five feet, vehicles could be drawn down it at a speed of twelve miles an hour with perfect safety. Gillespie says:
"It has been ascertained that a horse can for a short time double his usual exertion; also, that on the best roads he exerts a pressure against his collar of about one thirty-fifth of the load. If he can double his exertion for a time, he can pull one thirty-fifth more, and the slope which would force him to lift that proportion would be, as seen from the above table, one of one in thirty-five, or about a three per cent grade. On this slope, however, he would be compelled to double his ordinary exertion to draw a full load, and it would therefore be the maximum grade." Mr. Isaac B. Potter, an eminent authority upon roads, says:
"Dirty water and watery dirt make bad going, and mud is the greatest obstacle to the travel and traffic of the farmer. Mud is a mixture of dirt and water. The dirt is always to be found in the roadway, and the water, which comes in rain, snow, and frost, softens it; horses and wagons and narrow wheel tires knead it and mix it, and it soon gets into so bad a condition that a fairly loaded wagon cannot be hauled through it.
"We cannot prevent the coming of this water, and it only remains for us to get rid of it, which can be speedily done if we go about it in the right way. Very few people know how great an amount of water falls upon the country road, and it may surprise some of us to be told that on each mile of an ordinary country highway three rods wide within the United States there falls each year an average of twenty-seven thousand tons of water. In the ordinary country dirt road the water seems to stick and stay as if there was no other place for it, and this is only because we have never given it a fair opportunity to run out of the dirt and find its level in other places. We cannot make a hard road out of soft mud, and no amount of labor and machinery will make a good dirt road that will stay good unless some plan is adopted to get rid of the surplus water. Water is a heavy, limpid fluid, hard to confine and easy to let loose. It is always seeking for a chance to run down a hill; always trying to find its lowest level."
An essential feature of a good road is good drainage, and the principles of good drainage remain substantially the same whether the road be constructed of earth, gravel, shells, stones, or asphalt. The first demand of good drainage is to attend to the shape of road surface. This must be "crowned," or rounded up toward the center, so that there may be a fall from the center to the sides, thus compelling the water to flow rapidly from the surface into the gutters which should be constructed on one or both sides, and from there in turn be discharged into larger and more open channels. Furthermore, it is necessary that no water be allowed to flow across a roadway; culverts, tile, stone, or box drains should be provided for that purpose.