A brief, non-custodial traffic stop is considered a "seizure" for the purposes of the 4th Amendment and must therefore be supported by reasonable suspicion or probable cause. The investigating officer must weigh the totality of the circumstances to determine whether sufficient objective facts exist to create reasonable suspicion that the driver is engaged in criminal activity. If the investigating officer witnesses the driver commit a traffic violation (even if they are mistaken about what constitutes a violation, see "Heien v. North Carolina"), then said violation generally constitutes probable cause for the officer to stop the vehicle. The officer may detain the driver and any passengers of the vehicle for long enough to confirm and/or deny his or her suspicions.