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152 On rural two-lane sections of the system, whenever it is financially feasible to do so, the road shall be so designed in its horizontal and vertical curvature and other features as to afford a continuously unobstructed view for at least the following distance between points 4.5 feet above the road surface.

On sections so designed, drivers of vehicles moving at the design speed will have the assurance of a sufficient length of road, if no oncoming vehicle is in view, in which to accomplish the passing of another vehicle moving in the same direction at a speed 10 to 15 miles per hour slower. Passing at speeds above 65 miles per hour on two-lane roads generally cannot be considered safe, unless the vehicle passed is traveling at a speed considerably slower than that of the passing vehicle.

On rural two-lane sections of the system expected to carry an average daily traffic volume of 2,000 vehicles or more, where it is not feasible to provide the minimum passing sight distance recommended in table 3, two lanes shall be provided for traffic in each direction.

On all other two-lane sections of the system where the provision of the recommended minimum passing sight distance is not financially feasible, the longest practicable sight distance shall be provided.

Vertical curvature.—Vertica] curvature on all rural sections shall be of sufficient length over crests and in sags at underpasses to provide at least the minimum sight distance previously recommended for the assumed design speed, and, in other sags, to provide for safe and comfortable travel at the assumed design speed.

Number and width of traffic lanes and median strips.—All rural sections of the system expected to carry an average daily traffic of 15,000 or more vehicles shall provide three and not more than three lanes for traffic moving in each direction, each lane to have a width of 12 feet, and the lanes for traffic moving in opposite directions shall be separated by a median strip at least 15 feet wide.

All rural sections of the system expected to carry an average daily traffic of 3,000 but less than 15,000 vehicles shall provide at least two lanes for traffic moving in each direction, each lane to have a width of 12 feet; and the lanes for traffic moving in opposite directions shall be separated by a median strip at least 15 feet wide. On sections which permit crossing or entering at grade at intersecting highways or private entrances, the median strip at public road crossings shall be at least 40 feet wide, and opposite private-property entrances, at least 25 feet wide.

All rural sections of the system expected to carry an average daily traffic of 2,000 but less then 3,000 vehicles shall provide at least a two-lane pavement 24 feet wide. On all parts of such highways where it is not feasible to provide a sight distance at least equal to the minimum passing sight distance specified in table 3, the design of the highway shall provide two Janes for traffic moving in each direction.