The police officer must have a “reasonable suspicion based on articulable facts” that a law violation is occurring in order to stop your car. Any law violation is sufficient. For example, it is legal for a police officer to stop a car that crosses the centerline of the highway or that has a tail light out.
An officer can even stop a car that is weaving within the lane lines or the driver who fails to signal a turn or a lane change. However, if the officer makes a random stop of a driver and there is no articulable reason for doing so, it is possible that any evidence collected may later be kept out of court, including breath tests and the officer’s observations of the driver.