Page:The American Cyclopædia (1879) Volume XIV.djvu/369

 ROAD 353 and the extensive use of coal, were developed, the progress in road making was rapid. In the United States the importance of roads for military purposes, leading into the interior ter- ritories and to the frontier, was early appreci- ated, and some important routes were opened by the general government; as the national road from Baltimore, through Wheeling and Cincinnati, to St. Louis, and that from Bangor to Houlton in Maine. The making of turn- pike roads by chartered companies, before the general introduction of railroads, often yield- ed much profit to capitalists. Most of the paved road was constructed upon the Macadam principle. Several public turnpikes have been constructed in parts of New York and in the western states with planks ; but they have not proved successful, as the exposure to air and moisture causes them to decay rapidly. In laying out a new road, the general system re- sembles that for the construction of railways, but an equal expense in securing level grades is not usually justifiable. It is found that upon a slope of 1 in 44, or about 120 ft. to the mile, a horse can draw only three fourths as much as he can upon a level ; on a slope of 1 in 24, or 220 ft. to the mile, only half as much ; and on a slope of 1 in 10, or 528 ft. to the mile, only one fourth as much ; but these propor- tions vary with the condition of the road, be- cause when the road is soft the grade is vir- tually increased. The harder and firmer and smoother the surface of a road is, the less re- sistance it will offer to a passing wheel ; and for this reason elastic road beds are inferior for the transportation of heavy loads. It is usually estimated that the greatest inclination down which horses may trot with safety is, for roads paved with blocks, 1 in 60 ; for mac- adamized roads, 1 in 35 or 40 ; and for gravel or dirt roads, 1 in 15. In regard to the sur- face of a transverse section of a road, there has been considerable debate, some maintain- ing that it should be nearly straight, and that the drainage should be secured when practica- ble by longitudinal grading, the reason being that ease of draught on a convex road requires the wagon to be in the middle of the track. The weight of authority seems to be in favor of raising the track in the middle, but not to such a degree as to cause much inclination of the wagon. On roads where there is much traffic, so that wagons are continually meeting and passing, inclination may be avoided by having two tracks, each raised in the middle. To allow the water to run longitudinally upon a road bed for any considerable distance will certainly cause any macadamized or stone pavement to get out of order, from washing or undermining, unless it is laid in hydraulic cement, or asphalt of sufficient firmness to resist the action of a rapid current of water. In regard to the formation of the road bed there are two systems, that of Telford and that of Macadam. The system of Telford is principally a revival of that employed by the old Romans, and also adopted by Tr6saguet in France in 1760, but discarded in 1816 by Mac- adam, who substituted small angular broken stones, laying them directly upon the earth. (See PAVEMENT.) Telford made a return to the system of laying heavy stones at the bot- tom of the bed and covering them with a coat- ing of broken stones. Several excellent roads were constructed by him in Great Britain, the permanence of which is evidence of his engi- neering wisdom, such as that between Holy- head and Shrewsbury, and the Glasgow and Carlisle road. Macadam preferred a yielding to a rigid foundation, and even laid broken stone upon boggy ground. The angular shape of the stones caused them to bind together somewhat, but the superiority of roads having large stones or concrete (which is preferable since the manufacture of hydraulic cements has become so general) for a foundation is now generally conceded. The kind of stone most suitable for a road bed is a matter of im- portance; for macadamized roads, granite or basaltic rock, covered with sandstone or argil- laceous shale, is to be preferred. Slate rock in various degrees of hardness may often be employed with advantage as a surface cover- ing as well as a filling in many kinds of pave- ment where hydraulic cement is not relied on to produce firmness. Of the drainage of a road not much need be said, as it is evident that it should be comparatively dry, and not subject to inundation. A ditch at one or both sides, when the land does not slope away, is almost always necessary, and culverts to lead the water from one side to the other. In car- rying a road over a hilly country it is usual to wind* around the sides of hills and moun- tains, and an inclined plane of considerable length often becomes necessary. A ditch upon one side, with frequent culverts, should be constructed ; but it is sometimes the practice on turnpikes built by companies, and where the income of the road would not justify the outlay for construction and repair of culverts, to make diagonal elevations across the track at frequent intervals to direct the water off the road. If they are placed too far apart, the water is suffered to gather too much headway and thus wear away the road bed. It is this accelerated movement of water in the ditches of a road running down hill that makes it so difficult to construct culverts which shall re- ceive the current and conduct it away without damage to the banks along the roads. Pub- lic roads are laid out, constructed, regulated, and kept in repair by public authority. Pri- vate property is taken for the construction of roads upon allowance of just compensation to the owner. The system of making assessments for repairs varies in the different states. Gen- erally a property owners in the town or coun- ty where the road lies are assessed. In many of the states all male inhabitants 21 years old or over are required to labor on the roads a specified number of days each year, but a