for Macadam—Sizes of Stone—Earth Work—Foundation for the Macadam—Telford Foundation—Placing the Broken Stone—Rolling—Spreading Screenings—Bituminous Surfaces—Maintenance Characteristics

89-97

Chapter VIII

CEMENT CONCRETE ROADS

Destructive Agencies—Design—Concrete Materials—Fine Aggregate—Proportions—Measuring Materials—Preparation of the Earth Foundation—Placing Concrete for Two-course Road—Curing the Concrete—Expansion Joints—Reinforcing—Bituminous Coatings on Concrete Surfaces—Characteristics—Maintenance

98-105

Chapter IX

VITRIFIED BRICK ROADS

Vitrified Brick—Paving Brick—Repressed Brick—Vitrified Fiber Brick—Wire-cut-lug Brick—Tests for Quality—Other Tests—Foundation—Sand Bedding Course—Sand Mortar Bedding Course—Green Concrete Bedding Course—Bituminous Fillers—Mastic Fillers—Marginal Curb

106-115

Chapter X

BITUMINOUS ROAD MATERIALS AND THEIR USE

Classes of Bituminous Materials—Coal Tar—Water Gas Tar—Natural Asphalt—Petroleum Asphalt—Mixtures—Classification According to Consistency—Road Oils—Liquid Asphalts—Asphalt Cements—Fillers—Bitumen—Specifications—Surface Treatments—Applying the Bituminous Binder—Finishing the Surface—Patching—Penetration Macadam—Foundation—Upper or Wearing Course—Patching Characteristics—Hot Mixed Macadam—Foundation—Sizes of Stone—Mixing the Wearing Stone—Placing and Wearing Surface—Seal Coat—Characteristics—Asphaltic Concrete—Bitulithic or Warrenite—Topeka Asphaltic Concrete—Foundation—Placing the Surface—Characteristics

116-129

Chapter XI

MAINTENANCE OF HIGHWAYS

Petrol Maintenance—Gang Maintenance—Maintenance of Earth, Sand-clay, Gravel and Macadam Roads

130-134

Index

135

AMERICAN RURAL HIGHWAYS

Chapter I

THE PURPOSE AND UTILITY OF HIGHWAYS

The Development of Highway Systems

Transportation Problem.—Public highways, like many other familiar things, are utilized constantly with little thought of how indispensable they are to the conduct of the business of a nation or of the intimate relation they bear to the everyday life of any community. The degree to which a nation or a community perfects its transportation facilities is an index of its industrial progress and public highways constitute an important element in the national transportation system. It is to be expected that the average citizen will think of the public highway only when it affects his own activities and that he will concern himself but little with the broad problem of highway improvement unless it be brought forcibly to his attention through taxation or by publicity connected with the advancement of specific projects.

National in Scope.—The improvement and extension of the highway system is of national importance just as is development and extension of railways, and concerted action throughout a nation is a prerequisite to an adequate policy in regard to either. It is inconceivable that any community in a nation can prosper greatly without some benefit accruing to many other parts of the country. Increased consumption, which always accompanies material prosperity, means increased production somewhere, and people purchase from many varied sources to supply the things that they want. Good transportation facilities contribute greatly to community prosperity and indirectly to national prosperity, and the benefits of highly improved public highways are therefore national in scope. This fact has been recognized in Europe, notably in England, France and Belgium, where the public highways are administered largely as national utilities.

Until recent years, highway improvement in the United States has been subordinated to other more pressing public improvements, but during the World War the inadequacy of the transportation system of the United States became apparent. While such an unprecedented load upon transportation facilities may not recur for many years, it has become apparent that more rapid progress in highway improvement is necessary and in the United States the subject is now likely to receive attention commensurate with its importance.

Development of Traffic.—The character and extent of the highway improvement needed in any locality is dependent entirely on the demands of traffic. In sparsely settled areas, particularly those that are semi-arid or arid, the amount of traffic on local roads is likely to be small and the unimproved trails or natural roads adequate. But as an area develops either on account of agricultural progress or the establishment of industrial enterprises, the use of the public highways both for business and for pleasure increases and the old trails are gradually improved to meet, at least to some degree, the new demands of traffic. In sparsely settled areas, it is possible for the public to accommodate its use of the highways to the physical condition thereof, and business is more or less regulated according to the condition of the roads. This is not always pleasant or economical but is the only possible arrangement. In populous districts, with diversified activities, it becomes imperative to have year-round usable roads in order to transact with reasonable dispatch the regular business of the industries. Anything less will handicap normal community progress.

The advent of the motor driven vehicle in the United States has resulted in a greatly increased use of the public highways of agricultural areas, even of those that are sparsely populated, because of the convenience of the motor vehicle both for passenger and for freight service. Probably in excess of 90 per cent of the tonnage passing over the rural highways in the United States is carried by motor vehicles. This class of traffic has really just developed and no one can predict what it will be in ten years, yet it has already introduced into the highway problem an element that has revolutionized methods of construction and maintenance.

A different set of traffic conditions exists in those parts of the United States where large areas are devoted primarily to industrial pursuits, the agricultural development being of secondary importance. Public highways connecting the industrial centers are indispensable adjuncts to the business facilities in such communities and are ordinarily subjected to a very large volume and tonnage of traffic consisting principally of motor vehicles. The roads first selected for improvement will not be those serving the