The issue is whether there is probably cause to think a person who is intoxicated was driving the car. So if a car is parked or pulled over (or at a gas pump) and there is only one person with the car--i.e. the person with the car is obviously the driver--and that driver is drunk or impaired and the car is someplace other than the owner's home, so that the drunk or impaired person must have driven it there...in this case, the officer could certainly arrest.