Found it:
§ 3305. Limitations on overtaking on the left.
No vehicle shall be driven to the left side of the center or marked center line of the roadway in overtaking and passing another vehicle proceeding in the same direction
unless the left side is clearly visible and is free of oncoming traffic for a sufficient distance ahead to permit the overtaking and passing to be completely made without interfering with the operation of any vehicle approaching from the opposite direction or any vehicle overtaken. In every event the overtaking vehicle must return to an authorized lane of travel as soon as practicable and, in the event the passing movement involves the use of a lane authorized for vehicles approaching from the opposite direction, before coming within 200 feet of any approaching vehicle.
§ 3306. Limitations on driving on left side of roadway.
(a) General rule.--No vehicle shall be driven on the left side of the roadway under any of the following conditions:
(1) When approaching or upon the crest of a grade or a curve in the highway where the driver's view is obstructed within such distance as to create a hazard in the event another vehicle might approach from the opposite direction.
(2) When approaching within 100 feet of or traversing any intersection or railroad grade
crossing, unless otherwise indicated by official traffic-control devices.
(3) When the view is obstructed upon approaching within 100 feet of any bridge, viaduct or tunnel.
(b) Application of section.--This section does not apply under the conditions described in section 3301(a)(2),(3),(4) and (5) (relating to driving on right side of roadway).
§ 3307. No-passing zones.
(a) Establishment and marking.--The department and local authorities may determine those portions of any highway under their respective jurisdictions where overtaking and passing or driving on the left side of the roadway would be especially hazardous and shall by appropriate signs or markings on the roadway indicate the beginning and end of such zones and when the signs or markings are in place and clearly visible to an ordinarily observant person every driver of a vehicle shall obey the directions of the signs or markings. Signs shall be placed to indicate the beginning and end of each no-passing zone.
(b) Compliance by drivers.--Where signs and markings are in place to define a no-passing zone as set forth in subsection (a), no driver shall at any time drive on the left side of the roadway within the no-passing zone or on the left side of any pavement striping designed to mark a no-passing zone throughout its length.
http://www.dmv.state.pa.us/pdotforms/vehicle_code/chapter33.pdf