APPENDIX V
Basic Standards of Road and Structural Design
BASIC STANDARDS FOR RURAL SECTIONS
I. Roads.
Condition of access.—All rural sections of the system shall be established as limited-access highways, and access to the highway shall be permitted only at designated points at which facilities for safe entrance and exit shall be provided. There shall be no crossings of railways at grade, and all railways that must cross the interregional highway shall be carried over it or under it by means of adequate structures.
On all rural sections of the system expected to carry an average daily traffic of 5,000 or more vehicles there shall be no crossings of other highways at grade, and all highways that must cross the interregional highway shall be carried over it or under it by means of adequate structures.
Wherever feasible on all rural sections of the system expected to carry an average daily traffic of less than 5,000 vehicles, grade intersection with other highways shall be avoided and all highways that must cross the interregional highway shall be carried over or under by means of adequate structures. If, in any case, the grade separation of a highway intersection is not immediately feasible, all necessary provision shall be made in the initial design for future conversion to the improved design when financially feasible. This initial provision shall include public acquisition of private property or acquisition of control of the use and improvement of private property essential to conversion to the improved design. Where separation of grades at highway intersections is not feasible, and at all points where vehicles may be expected to cross, enter, or leave the interregional highway, the design shall be such as to insure a high degree of safety in crossing, entering or leaving it, without installation of traffic control signals, which shall in no case be employed.
Location.—The location between control points shall be as direct as feasible and shall conform to the topography in such manner as to avoid the appearance of forced alinement. Where four or more traffic lanes are to be constructed, two distinct one-way roads should be provided rather than a divided highway of fixed cross section, wherever advantages of alinement, construction cost, or traffic facility may be expected to result from such provision.
Alinement.—Alinement of rural sections of the system shall be of as high a standard as feasible; and the speed assumed for design purposes for a section of road shall be as high as practicable, consistent with the topography and the expected traffic volume. The design speeds assumed for adjacent sections of the highway shall not differ widely.
Horizontal curvature.—Horizontal curvature shall be under all conditions of the lowest practicable degree, and at no point sharper than the degree shown in the column headed “Absolute maximum”? in the
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