PENNSYLVANIA LAWS AND RESEARCH

Duties at stop signs.--Except when directed to proceed by a police officer or appropriately attired persons authorized to direct, control or regulate traffic, every driver of a vehicle approaching a stop sign shall stop at a clearly marked stop line or, if no stop line is present, before entering a crosswalk on the near side of the intersection or, if no crosswalk is present, then at the point nearest the intersecting roadway where the driver has a view of approaching traffic on the intersecting roadway before entering. If, after stopping at a crosswalk or clearly marked stop line, a driver does not have a clear view of approaching traffic, the driver shall, after yielding the right-of-way to any pedestrian in the crosswalk, slowly pull forward from the stopped position to a point where the driver has a clear view of approaching traffic. The driver shall yield the right-of-way to any vehicle in the intersection or approaching on another roadway so closely as to constitute a hazard during the time when the driver is moving across or within the intersection or junction of roadways, and enter the intersection when it is safe to do so.

Duties at yield signs.--The driver of a vehicle approaching a yield sign shall in obedience to the sign slow down to a speed reasonable for the existing conditions and, if required for safety to stop, shall stop before entering a crosswalk on the near side of the intersection or, if none, then at the point nearest the intersecting roadway where the driver has a view of approaching traffic on the intersecting roadway before entering. After slowing down or stopping, the driver shall yield the right-of-way to any vehicle in the intersection or approaching on another roadway so closely as to constitute a hazard during the time the driver is moving across or within the intersection of roadways. If a driver is involved in a collision with a vehicle in the intersection or junction of roadways after driving past a yield sign, the collision shall be deemed prima facie evidence of failure of the driver to yield the right-of-way.

Driving under influence of alcohol or controlled substance - A person shall not drive, operate or be in actual physical control of the movement of any vehicle:
while under the influence of alcohol to a degree which renders the person incapable of safe driving;
while under the influence of any controlled substance, as defined in the act of April 14, 1972 (P.L. 233, No.64) known as the Controlled Substance, Drug, Device and Cosmetic Act, to a degree which renders the person incapable of safe driving;
while under the combined influence of alcohol and any controlled substance to a degree which renders the person incapable of safe driving;
while the amount of alcohol by weight in the blood of:
an adult is 0.08% or greater; or
a minor is 0.02% or greater.