William Rehnquist

“ We observed that the random stops involved the "kind of standardless and unconstrained discretion [which] is the evil the Court has discerned when in previous cases it has insisted that the discretion of the official in the field be circumscribed, at least to some extent." Id., at 661, 99 S.Ct., at 1400. We went on to state that our holding did not "cast doubt on the permissibility of roadside truck weigh-stations and inspection checkpoints, at which some vehicles may be subject to further detention for safety and regulatory inspection than are others." ”

“ Prouse, supra, we disapproved random stops made by Delaware Highway Patrol officers in an effort to apprehend unlicensed drivers and unsafe vehicles. We observed that no empirical evidence indicated that such stops would be an effective means of promoting roadway safety and said that " [i] t seems common sense that the percentage of all drivers on the road who are driving without a license is very small and that the number of licensed drivers who will be stopped in order to find one unlicensed operator will be large indeed." ”

“ Roving patrols often operate at night on seldom-traveled roads, and their approach may frighten motorists. At traffic checkpoints the motorist can see that other vehicles are being stopped, he can see visible signs of the officers' authority, and he is much less likely to be frightened or annoyed by the intrusion. ”

“ Each of the respondents "is a licensed driver in the State of Michigan . . . who regularly travels throughout the State in his automobile." See Complaint, App. 3a-4a. During pretrial proceedings, petitioners agreed to delay further implementation of the checkpoint program pending the outcome of this litigation.
After the trial, at which the court heard extensive testimony concerning, inter alia, the "effectiveness" of highway sobriety checkpoint programs, the court ruled that the Michigan program violated the Fourth Amendment and Art. ”