provided, if financially feasible, an area not less than 10 feet wide, which shall be reserved for the temporary accommodation of disabled or other stationary vehicles.
Drainage.—For the removal of drainage from the pavements, median strips, shoulders, or standing areas, and adjacent slopes of urban sections of the system, an underground drainage system shall be constructed, entrance to which shall be provided at suitable intervals and in appropriate places by means of drop inlets of adequate design and capacity, in such manner as to avoid all possible hazard to traffic and reduction of the traffic capacity of the pavements.
Gradient.—The gradient of urban sections of the system shall preferably be not steeper than 3 percent and shall in no case exceed 5 percent. In general, extremely long grades should be less steep and very short ones may be steeper than grades of moderate length. Grades to be traveled only in the downward direction on one-way roads may be steeper than the limits recommended above.
Width of right-of-way.—The right-of-way to be acquired for urban sections of the interregional system shall be at least sufficient to permit the construction of pavements, median strips, areas for deceleration, acceleration, and maneuvering, standing areas, side slopes, ramps, retaining walls, barrier strips, and service streets, or such of these facilities as may be required at any point, all constructed in accordance with the foregoing recommendations. The required right-of-way shall be acquired in its entirety by outright purchase or condemnation in accordance with the need for the planned ultimate development of the highway.
Foundations and bases, surfaces, and pavements.—All road foundations and bases, and all road surfaces and pavements on urban sections of the system shall conform to the basic standards hereinbefore recommended for foundations, bases, surfaces, and pavements on rural sections of the system.
II. Bridges and culverts.
Definitions.—All structures shall be classed as long bridges, short bridges, or culverts as hereinbefore recommended for rural sections of the system.
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 urban sections of the system recommended herein under “I. Roads.”
Width of bridges.—The width between vehicular curbs on all bridges built on tangents of urban sections of the system shall be at least 4 feet greater than the width of the 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 2 feet. Where the approach pavements have curbs adjoining the outer lanes thereof, curbs on the approaches and on the bridge shall be continuous.
On all bridges the lateral distance from the face of the curb to the face of the bridge rail or any structural member shall be at least 18 inches and as much more as is necessary for walk space. Where curbs on a bridge are continuous with curbs adjoining the outer lanes.
