75 Pa. C. S. § 3303. Overtaking vehicle on the left

    (a) GENERAL RULE.-- The following rules shall govern the overtaking and passing of vehicles proceeding in the same direction, subject to the limitations, exceptions and special rules stated in this chapter:
 
(1) The driver of a vehicle overtaking another vehicle proceeding in the same direction shall pass to the left of the other vehicle at a safe distance and shall stay to the left of the other vehicle until safely clear of the overtaken vehicle.

(2) Except when overtaking and passing on the right is permitted, the driver of an overtaken vehicle shall not increase the speed of the vehicle until completely passed by the overtaking vehicle and shall give way to the right in favor of the overtaking vehicle on suitable signal.
 
   (b) SUITABLE SIGNAL DEFINED.-- Suitable signal for purposes of subsection (a)(2) shall be as follows:
 
(1) At all times when head lamps are required to be lighted according to section 4302 (relating to the period for requiring lighted lamps), an audible signal or the intermittent flashing of low and high beams except that the use of high beams shall not be permitted when a vehicle is approaching from the opposite direction within 500 feet.

(2) At all other times, an audible signal.