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116 will need to be alive to a wide range of possible conditions, and prepared to cope with any conditions that may eventuate, when they occur. For such an approach to post-war planning, the past quarter of a century has provided important signs and guideposts.

CONSTRUCTION ACTIVITY AND NATIONAL INCOME

The Committee has analyzed the records of construction during this past period in an effort to discover the relations that have existed between total construction volume and the aggregate economy. It has attempted to identify the underlying conditions which have made for a varying relation in amount between public and private construction; to ascertain the magnitude of Federal in relation to total public construction expenditures; and particularly to examine the amount and character of Federal expenditures for highway construction in relation to the resulting benefits and employment.

Data available for these purposes, embracing the period from 1915 through 1942, are tabulated in detail in appendix VII, table 1. These data have been considered in 4-year periods, selected to reflect the variant relations of the several classes of construction, during two war periods, in prosperity and in depression, and in the rising and falling economy of the transitional periods between. The Committee believes that among these relations will be found analogies suggestive of a desirable pattern of expenditure for the post-war period.

The broad relations of total construction volume and the aggregate economy are shown in table 21, which compares the total estimated cost of construction, including work relief and maintenance, with the national income in the typic periods.

National income and construction activity associated.—Throughout all periods from 1915 to 1942, it is apparent from table 21 that fluctuations of the national income and the volume of construction activity, both measured in dollars, have been closely linked. Rising income has been accompanied by increasing construction activity. Declining construction activity has coincided with falling income. There is also an evident tendency, when income is rising, for construction activity to supply in increasing measure the source of the income,