75 Pa.C.S. § 3304: Overtaking vehicle on the right.

(a) General rule.--The driver of a vehicle may overtake and pass upon the right of another vehicle only under one of the following conditions:

(1) When the vehicle overtaken is making or about to make a left turn, except that such movement shall not be made by driving off the berm or shoulder of the highway.

(2) Upon a roadway with unobstructed pavement of sufficient width for two or more lines of vehicles moving lawfully in the direction being traveled by the overtaken vehicle, except that such movement shall not be made by driving off the roadway.

(b) Limitation.--No passing movement under this section shall be made unless the movement can be made in safety.