In the beginning of the movement various experiments were tried, such as steel-tracked roadways, but time-approved methods of im provement soon became standard. For many parts of the country the ordinary dirt road is probably the only economical type. When sur faced with a proper mixture of sand and clay, or topsoil, kept smooth and hard by the fre quent use of a ((road drag,n and well drained, it makes a very serviceable roadway throughout the year, with the possible exception of the early spring months. This type of road has been the object of considerable engineering study, especially in the States of the great cen tral valley of the United States. About one sixth of the total 30,000 miles of State-aid roads in 1915 were of this sand-clay type.
Nearly one-half the total come under the classification of ((gravel roads,D a grade better than the sand-clay. These can be built for $2,500 to $4,000 a mile, and the cost of main taining them generally does not exceed $250 a mile per year. Often these are built of bank run gravel, but more generally a certain propor tion of sand and day or loam is mixed with the gravel to give the mixture the necessary bind ing qualities.
The best type of roads are, of course, the macadamized, similar to gravel roads, but with more binding. Instead of small pieces of stone in the forin of pebbles and natural fragments, artificially produced fragments are used, and instead of sand and loam, rock dust is employed as the binding material. This broken stone is placed in layers and rolled with heavy steam road rollers. These roads, sprinkled with water before first rolling, are called 'water boon& macadam. Distinguished from it is the macadam)) in which asphaltic or tar binding material is used, either in place of, or in addition to, the rock dust. Also, many gravel and water-bound macadam roads, either immediately after completion or subsequently, are treated with a surface coating of liquid bi tuminous binder, sprinkled over with a layer of sand or stone chips. These are practically pavements.
Both gravel and water-bound macadam roads reqwre ceaseless vigilance in maintenance and without this they rapidly go to pieces under motor vehicle traffic. The pneumatic tires of motor vehicles appear to be very destructive, especially in dry weather, by out the dust binding material and causing the surface to °ravel." Hence the vital importance of clauses in road laws relative to maintenance. To pre vent this disintegration there is a great variety of materials, patented and unpatented, to be applied to road surfaces. These vary all the
way from common salt and calcium chloride to the many bituminous compounds, e.g., Dusto line, Glutrine, Rocmac and numerous petroleum and tar products. These are all either "dust layers" or "road binders." Dust layers are in tended to hold the dust in the road by keep ing the surface damp (as in the case of salt and calcium chloride) or by the capillary attraction of an oily liquid. The road binders have such adhesive or cementive qualities as to replace the dust as a binder and keep the road surface intact.
Other phases of the good roads movement which are important are the relocation of roads; the elimination of grades, elimination of grade crossings, the closing of unnecessary or little used roads; the provision of proper drainage; legislation regarding wagon tires and weeds; the abolition of toll roads. In some States the movement has entered into the esthetics of road improvement, beautifying the roads with trees, erecting sign posts at cross roads, naming farms.
A new interest in the economics of road improvement has been a decided factor in the movement. It is now realized that the first cost is high but the resultant gain great, be cause of the increased volume of traffic on them. Nearly 100,000,000,000 pounds of farm products are annually hauled from farms to shipping points and to this must be added the enormous weight of products hauled from farms to mills and from mills back to farms; as well as the truck, forest and mine products, and the city products that go out into the coun try. The average cost of hauling per ton mile is about 25 cents, which foreign experience as well as government investigations have shown could be reduced to at least 12 cents or 50 per cent, making a possible saving of over $50,000, 000 or about the amount now annually ex pended in direct State aid. The Good Roads Association was formed in 1892 and immedi ately resulted in increased interest. The separate States have also formed good roads associations, and the meetings and reports of these and the national association play an im portant part in disseminating and arousing interest. The extension of rural mail service has been of some effect upon improve ment of roads. In 1917 about 500,000 miles of roads were described and used as post routes. Indeed every phase of rural betterment calls for better roads. The movements to the cen tralization and consolidation of schools is closely connected with the condition of the roads.