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Rh Wherever feasible, it is desirable on rural sections of the system that public control be obtained at the outset over a strip of land 300 feet wide without regard to the expected traffic volume on the highway.

Where it is necessary at the time of construction or where it will probably be necessary at a later date to provide service roads to permit use of the interregional highway as a limited-access highway, sufficient width for the construction of such service roads shall also be included in the width of right-of-way to be initially acquired.

Foundations and bases.—All road foundations and bases on rural sections of the system shall be capable of supporting the recommended maximum loads of vehicles as such loads are transmitted by surfaces or pavements of adequate design, without reduction of load or speed at any season of the year.

Surfaces and pavements.—All road surfaces and pavements on rural sections of the system shall consist of such material and shall be of such thickness as will enable them, when placed on bases and foundations of adequate design, to support the recommended maximum loads of vehicles, without reduction of either load or speed at any season of the year; and shall be capable of retaining under traffic of the expected weight, speed, and volume, with a reasonable expenditure of maintenance effort, a uniformly dustless, mudless, and smooth but skid-resistant surface.

Shoulders.—All road shoulders on rural sections of the system shall contrast in texture and preferably in color with the adjoining surface or pavement. They shall be capable of supporting the recommended maximum loads of vehicles standing on them or passing onto them infrequently and in emergency at high speed, and shall be capable of retaining under such usage, with a reasonable expenditure of maintenance effort, a reasonably mudless and even surface, without dangerous difference of level at the line of junction with the road surface or pavement.

''II. Bridges and culverts.''

Definitions.—All structures of a length between abutments greater than 20 feet, measured along the center line of the road, shall be defined as bridges.

All bridges of a length between abutments greater than 100 feet shall be classed as long bridges.

All bridges of a length of 100 feet or less shall be classed as short bridges.

All structures of a length between abutments of 20 feet or less, measured along the center line of the road, shall be defined as culverts.

Alinement of bridges.—All bridges, wherever feasible, shall be so located as to fit the over-all alinement and gradient of the highway and shall be subordinated thereto. Where structural or architectural requirements make it desirable to adjust the alinement and gradient of the highway, the changes shall be such that the highway will meet all the basic standards for rural sections of the system, recommended herein under “I. Roads.”

Width of bridges.—The width between vehicular curbs on all bridges built on tangents of rural sections of the system shall be at least 6 feet greater than the width of the surface or pavement of the approach highway, and the lateral distances between the edges of the pavement of the approach: highway and the faces of the vehicular curbs shall be at least 3 feet.