A brief, non-custodial traffic stop must normally be supported by reasonable suspicion; 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.
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.