Most Chester County DUI's occur because the police allege that a traffic violation occurs. In some cases, however, a Chester County DUI lawyer sees a case where a person is arrested after a "mere encounter". This can include a "welfare check" or a casual "hello" from a police officer or trooper. No reasonable suspicion or probable cause is needed in these cases.
In these cases, you have to be very careful about the specifics of the case. Potentially, a legal defense is that the "encounter" was pretextual. Two main cases that stick out are Commonwealth v. Collins from 2008 and Commonwealth v. Kendall from 2009.
In Collins, the defendant was in a vehicle parked legally, at night, at an overlook, an officer approached, and defendant blurted out that he was smoking marijuana. The appellate court held this initial interaction was a mere encounter. The interaction was first a mere encounter because a reasonable person in defendant's position would be free to terminate it. The officer parked 20 feet from the rear of the vehicle and did not turn on his overhead lights. The vehicle was not obstructing traffic or violating any traffic regulations. While people parked here regularly, they did not do so as frequently after dark, so the officer was concerned enough to check on the vehicle's condition and the occupants' safety.
The officer saw no outward sign of distress, nor anything leading him to think illegal activity was occurring. He said the occupants did not act as if they were trying to get away. Instead, the officer asked if "everyone was ok," and defendant said they were smoking marijuana, at which time the officer smelled burnt marijuana and saw a bong in the vehicle. The facts did not show the officer acted in a coercive manner or spoke forcefully.
In Kendall, a patrol car was following defendant's car for approximately two or three minutes when defendant activated his turn signal and pulled off to the shoulder (where they would legally park!). The officer testified that as there was no driveway or anything else nearby, there was no reason for defendant to be pulling off; the officer thought of possible vehicle failure. The officer pulled behind defendant and activated his overhead lights. He exited his patrol car, approached the car, and asked defendant why he suddenly pulled over; defendant replied that it was to let the patrol car pass. The officer smelled alcohol on defendant's breath, and noted his slurred speech and glassy eyes. After defendant failed a field sobriety test, he was arrested for DUI. Defendant argued that the stop was not supported by reasonable suspicion.
The appellate court held that as the evidence allowed the trial court to conclude that the officer was trying to determine if defendant needed assistance, his interaction with defendant was a mere encounter, which required no level of suspicion. That the officer triggered his overhead lights at nighttime to alert passing cars did not shift the interaction to an investigatory detention.
Thus, a person has to be careful just being stopped on the side of the road as an officer can approach for a mere encounter.