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Where current revenues do not provide sufficient funds for urgently needed road improvements, borrowing is justified. It is generally held that highway debt should be repaid within the life of the improvements made. Highway surfaces wear out and must be replaced, but grading has permanent value and drainage structures last for a long time. When a surface is worn out, it still has value as a base for a new surface. One third or more of the cost of a new highway may be for improvements that will be of value for many years after the original surface is replaced.

Highway Types and Standards.—The type if soil on which a highway surface is placed has ;reat influence on the durability and character if the roadbed. Coarse-grained, sandy soils give ;ood results, but fine-grained soils, such as clay, re unfavorable, requiring thick base courses. Im-'ortant progress has been made in studying soils nd developing tests that indicate their character-stics. There are also chemicals that improve the haracter of soil as a road surface, but there is as et no chemical available in sufficient quantity or t a price low enough to permit its general use i improving earth roads.

The surveys also assembled t facts needed for an estimate of the cost of bur ing and maintaining the improved highway si tem, and made possible the establishment of in" grated programs of highway improvement tf were both socially defensible and economical sound. Field work consisted of (1) a road inve tory in which conditions of road surface, widl curvature, and grades were recorded; (2} cour ing of traffic to determine service rendered; ai (3) study of road use and finance to determi: the extent to which roads were used by vario groups and the extent to which each group co: tributed to highway funds. The pattern set the United States has been followed, with some modification, in a number of countries.