An unknown motorist traveling eastbound struck and killed a 70-year-old bicyclist. The motorist drove off without identifying himself. About one week later at about the same time of night and about the same place, local police set up a highway checkpoint designed to obtain more information about the accident from the motoring public. As each vehicle drew up to the checkpoint, an officer would stop it for 10 to 15 seconds, ask the occupants whether they had seen anything happen there the previous weekend, and hand each driver a flyer. The flyer said 'ALERT ... FATAL HIT & RUN ACCIDENT' and requested 'assistance in identifying the vehicle and driver in this accident which killed a 70-year-old bicyclist.' Lidster (D) drove a minivan toward the checkpoint. As he approached the checkpoint, his van swerved, nearly hitting one of the officers. The officer smelled alcohol on Ds breath. He directed D to a side street where another officer administered a sobriety test and then arrested D. Lidster was tried and convicted in Illinois state court of driving under the influence of alcohol. The trial court rejected D's Fourth Amendment challenge. But an Illinois appellate court reached the opposite conclusion. The Illinois Supreme Court agreed with the appellate court. It held (by a vote of 4 to 3) that our decision in Indianapolis v. Edmond, 531 U. S. 32 (2000), required it to find the stop unconstitutional.