If you can figure out what Commonwealth v. Feczko, 10 A.3d 1285 (Pa. Super. 2010), means in terms of criminal defense practice, feel free to share.
This opinion came out in December, and I had a chance to read it in detail today. As near as I can tell, it recognizes two types of Motor Vehicle Code (Title 75) violations: those that are "investigatable" (for which the purposes of a Terry stop exist - maintaining the status quo while investigating) and those in which there is nothing further to investigate.
"Mere reasonable suspicion will not justify a vehicle stop when the driver's detention cannot serve an investigatory purpose relevant to the suspected violation." Feczko, at PA SUPER p. 12 (no star numbers available).
So, for offenses that require no further investigation, such as speeding violations, probable cause is required. But for offenses that may require further investigation, such as DUI, only reasonable suspicion is necessary.
(What a ridiculous mess our DUI jurisprudence has become. I'm going to think about that tonight and may update again this weekend.)