The Future of Road-making in America

by Archer Butler Hulbert

When the road passes through villages and towns the grading should reduce the roadbed to a grade as nearly level as possible. It must be borne in mind that the side ditches need not necessarily always conform to the center grade of the road. When the center grade is level the side ditches should be graded to carry off the water. In some cases I have found it necessary to run the grade for the side ditches in an opposite direction from the grade of the road. This, however, does not often occur. The main thing is to get the water off the road as soon as possible after it falls, and then not allow it to remain in the ditches. And just here the engineer will meet with many difficulties. The landowners in rural districts are opposed to having the water from the roads let onto their lands, and disputes often arise as to where the natural water way is located. This should be determined by the people in the neighborhood, or by the local authorities. I have found in several cases, where the water from side ditches was allowed to run on the land, that the land was generally benefited by having the soil enriched by the fertilizing matter from the road.

After the roadbed has been thoroughly prepared, if made of loam or clay, it should be rolled and made as hard and compact as possible. Wherever a depression appears it should be filled up and made uniformly hard. Place upon it a light coat of loam or fine clay, which will act as a binder. If the roller used is not too heavy it may be rolled to advantage, but the rolling of this course depends upon the character of the stones. If the stones are cubical in form rolling is beneficial, but if they are of shale and many of them thin and flat, rolling has a tendency to bring the flat sides to the surface. When this is the case the next course of fine stone for the surface will not firmly compact and unite with them.

When the foundation is of telford it is important that stones not too large should be used. They should not exceed ten inches in length, six inches on one side, which is laid next to the earth, and four inches on top, the depth depending on the thickness of the road. If the thickness of the finished road is eight inches, the telford pavement should not exceed five inches; if it is ten or more inches deep, then the telford could be six inches. It need in no case be greater than this, as this is sufficient to form the base or foundation of the metal construction. The surface of the telford pavement should be as uniform as possible, all projecting points broken off, and interstices filled in with small stone. Care should be taken to keep the stone set up perpendicular with the roadbed and set lengthwise across the road with joints broken. This foundation should be well hammered down with sledge hammers and made hard and compact. Upon this feature greatly depends the smoothness of the surface of the road and uniform wear. If put down compactly rolling is not necessary, and if not put down solid rolling might do it damage in causing the large stones to lean and set on their edges instead of on the flat sides. I refer to instances where the road is to be ten inches and over. Then put on a light coat or course of one and one-half inch stone, with a light coat of binding, and then put on the roller, thus setting the finer stone well with the foundation and compacting the whole mass together.

After the macadam or telford foundation is well laid and compacted, the surface or wearing stone is put on. If the thickness of the road is great enough, say twelve or fourteen inches, this surface stone should be put on in courses, say of three and four inches, as may be required for the determined thickness of the road. On each course there should be applied a binding, but only sufficient to bind the metal together or fill up the small interstices. It must be remembered that broken stone is used in order to form a compact mass. The sides of the stone should come together and not be kept apart by what we call binding material; therefore only such quantity should be used as will fill up the small interstices made by reason of the irregularity of the stone. Each course should be thoroughly rolled to get the metal as compact as possible. When the stone construction is made to the required depth or thickness, the whole surface should be subjected to a coat of screenings about one inch thick. This must be kept damp by sprinkling, and thoroughly rolled until the whole mass becomes consolidated and the surface smooth and uniform. Before the rolling is finished the shoulders should be made up and covered with gravel or other hard earth and dressed off to the side ditches. When practicable these should have the same grade or slope as the stone construction. This finish should also be rolled and made uniform, so that, in order that the water may pass off freely, there will be no obstruction between the stone roadbed and side ditches. To prevent washes and insure as much hardness as possible on roads in rural districts, grass should be encouraged to grow so as to make a stiff sod.

For shouldering, when the natural soil is of soft sand, a stiff clay is desirable. When the natural soil is of clay, then gravel or coarse sand can be used, covering the whole with the ditch scrapings or other fertilizing material, where grass sod is desirable. Of course this is not desirable in villages and towns.

For binding, what is called garden loam is the best. When this cannot be found use any soft clay or earth free from clods or round stones. It must be spread on very lightly and uniformly.

Any good dry stone not liable to disintegrate can be used as metal for foundation for either telford or macadam construction. For the surface it is necessary to have the best stone obtainable. Like the edge of a tool, it does the service and must take the wear. As in the tool it pays to have the best of steel, so on the road, which is subject to the wear and tear of steel horseshoes and heavy iron tires, it is found the cheapest to have the best of stone.

It is difficult to describe the kind of stone that is best. The best is generally syenite trap rock, but this term does not give any definite idea. The kind used in New Jersey is called the general name of Jersey trap rock. It is a gray syenite, and is found in great quantities in a range running from Jersey City, on the Hudson River, to a point on the Delaware between Trenton and Lambertville. There are quantities of good stone lying north of this ledge, but none south of it.

The best is at or near Jersey City. The same kind of stone is found in the same ranges of hills in Pennsylvania, but in the general run it is not so good. The liability to softness and disintegration increases after leaving the eastern part of New Jersey, and while good stone may be found, the veins of poorer stone increase as we go south and west.

It is generally believed that the hardest stones are best for road purposes, but this is not the case. The hard quartz will crush under the wheels of a heavy load. It is toughness in the stone that is necessary; therefore a mixed stone, like syenite, is the best. This wears smooth, as the rough edges of the stone come in contact with the wheels. It requires good judgment based on experience to determine the right kind of stone to take the constant wear of horseshoes and wagon tires.