Indianapolis began to operate vehicle checkpoints in an effort to interdict unlawful drugs. The city conducted six such roadblocks between August and November that year, stopping 1,161 vehicles and arresting 104 motorists. Fifty-five arrests were for drug-related crimes, while 49 were for offenses unrelated to drugs. The overall 'hit rate' of the program was thus approximately nine percent. The police stop a predetermined number of vehicles. Approximately 30 officers are stationed at the checkpoint. Pursuant to written directives issued by the chief of police, at least one officer approaches the vehicle, advises the driver that he or she is being stopped briefly at a drug checkpoint, and asks the driver to produce a license and registration. The officer also looks for signs of impairment and conducts an open-view examination of the vehicle from the outside. A narcotics-detection dog walks around the outside of each stopped vehicle. The officers were only allowed to conduct a search by consent or based on the appropriate quantum of particularized suspicion. The officers must conduct each stop in the same manner until particularized suspicion develops, and the officers have no discretion to stop any vehicle out of sequence. The city agreed in the stipulation to operate the checkpoints in such a way as to ensure that the total duration of each stop, absent reasonable suspicion or probable cause, would be five minutes or less. The checkpoint locations were selected weeks in advance based on such considerations as area crime statistics and traffic flow. The checkpoints are generally operated during daylight hours and are identified with lighted signs reading, 'NARCOTICS CHECKPOINT ___ MILE AHEAD, NARCOTICS K-9 IN USE, BE PREPARED TO STOP.' James Edmond and Joell Palmer (P) were each stopped at a narcotics checkpoint and then filed a lawsuit on behalf of themselves and the class of all motorists who had been stopped or were subject to being stopped. Ps claimed that the roadblocks violated the Fourth Amendment and the search and seizure provision of the Indiana Constitution. Respondents requested declaratory and injunctive relief for the class, as well as damages and attorney's fees for themselves. Ps then moved for a preliminary injunction. The District Court agreed to class certification and denied the motion for a preliminary injunction, holding that the checkpoint program did not violate the Fourth Amendment. A divided panel of the United States Court of Appeals for the Seventh Circuit reversed, holding that the checkpoints contravened the Fourth Amendment. The Supreme Court granted certiorari.