Probable Cause Standard

There are many good cases where probable cause to arrest is explained.  "Where there is a reasonable suspicion of criminal activity or of a passenger's being armed and dangerous, a police officer may order a passenger to alight from a vehicle that has been stopped for a traffic violation. Commonwealth v. Elliott, 376 Pa.Super. 536, 546 A.2d 654 (1988). An arresting officer need not expose himself or herself to potential injury from a passenger during the course of an investigation being conducted to determine if the vehicle is stolen. Once the officer formed the reasonable  belief that the car may have been stolen, he was legally entitled to take the protective step of removing all the occupants from the car in order to examine the VIN on the dashboard. The United States Supreme Court has recognized the significance of the VIN and the necessity of safeguarding an officer's physical well-being during an investigation to determine it. HN2A demand to inspect the VIN is within the scope of police authority pursuant to a traffic violation stop. New York v. Class, 475 U.S. 106, 115, 106 S.Ct. 960, 966, 89 L.Ed.2d 81, 91 (1986). Since the officer had authority to inspect the VIN, it follows that he may take reasonable precautions against physical harm that may be inflicted by any occupant of the vehicle". Commonwealth v. Robinson, 399 Pa. Super. 199, 203-204 (Pa. Super. Ct. 1990)

Thus, if a police officer has an "articulable and reasonable ground" to suspect a violation of the Vehicle Code enough to stop a vehicle, he may then order a defendant out of his car.  As the Commonwealth v. Rodriguez court stated in 1997, all occupants of a lawfully stopped vehicle may be ordered from the vehicle.  

Probable Cause for DUI

A Chester County DUI lawyer is well-versed in the Commonwealth v. Klingensmith case from 1994, In this case, appellant challenged his conviction for driving under the influence of alcohol, driving with suspended operating privileges, and driving without a registration plate. Appellant alleged that he was arrested without probable cause, that the intoxilyzer results should have been suppressed because appellant was not given his Miranda rights or his implied consent obligation under state law, and that he was subject to an illegal sentence. The court affirmed appellant's conviction because the police validly stopped appellant when the police observed that he was driving a car without a registration plate. Appellant's subsequent failure of the sobriety tests gave the police probable cause to arrest appellant for driving under the influence of alcohol. Appellant was not entitled to receive Miranda warnings. 

Appellant told the officer that he had been arrested five times for driving under the influence, that he knew the implied consent warning, and that he consented to the test. The trial court had discretion to impose consecutive sentences for the charges under which appellant was convicted.

So, the lead up in the PC for DUI in Chester County is -- proper stop, suspicion of DUI gained through observations and field sobriety tests and visual cues.