Passing Vehicles Proceeding in Opposite Directions. (a) Operators of vehicles proceeding in opposite directions shall pass each other to the right and, except when a highway has been divided into traffic lanes, each operator shall give to the other at least one-half of the main travel portion of the highway whenever possible. (b) Whenever upon any grade the width of the highway is insufficient to permit the passing of vehicles approaching from opposite directions at the point of meeting, the operator of the vehicle descending the grade shall, if necessary, back that vehicle to a place in the highway where it is possible for the vehicles to pass. Source: PL 3-61, § 1 (§ 516).