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26 DESIGN STANDARDS FOR BRIDGES AND HIGHWAYS

The design standards for bridges and roads adequate to serve the national-defense requirements have been the subject of consultation with representatives of the War Department over a long period. As here presented, the desirable minimum requirements have the endorsement of the War Plans Division of the General Staff. The design requirements as to structural capacity of bridges and standard pavements which have been applied to Federal-aid projects are consistent with the minimum requirements approved by the War Plans Division. Through the years there have been frequent criticisms that the Federal-aid policies required unnecessarily high standards. An adequately improved road system for a State or a nation is the product of long years of construction effort and the expenditure of vast sums. Now suddenly confronted with a great national emergency, every really adequate bridge or mile of paved road is an asset of greater value than its cost in terms of national security. This report indicates a considerable volume of work of an emergency character. It is relatively small when account is taken of the large number of Army and Navy reservations for many purposes, the huge production programs, new housing developments, and the 74,600 miles of the strategic network. For example, of the 16,692, bridges on rural sections of the strategic network, only 2,436 are listed as substandard in their capacity to carry the heaviest equipment and ordnance yet proposed.

The recommended design standards for military usage are discussed in detail for the purpose of estimating the present adequacy of roads certified as important to the national defense, locating definitely the places at which improvements are desirable, and determining the character and costs of such improvements. Roads and bridges conforming in their design to these standards will generally be completely adequate for the service of both the normal civil and extraordinary defense needs.

DESIGN STANDARD APPLICABLE TO RURAL AREA

For bridges and highways in rural areas the desirable standards are as follows:

Bridges. Load capacity.—Load capacity conforming to the recently revised standard H–15 live loading recommended by the American Association of State Highway Officials. This design loading consists of a standard truck having a total weight with load of 15 tons, or of lane loads equivalent to the truck train loading included in the 1935 specifications of the American Association of State Highway Officials.

The manner in which these truck and lane loadings are to be applied in the design of structures is specified as follows:

The lane loadings or standard trucks shall be assumed to occupy traffic lanes, each having a width of 10 feet corresponding to the standard truck clearance width. Within the curb-to-curb width of the roadway, the traffic lanes shall be assumed to occupy any position