A DUI checkpoint (also referred to as a sobriety checkpoint or DUI roadblock), is one method law enforcement uses to test drivers for intoxication. Checkpoints are usually set up at intersections and during times when impaired driving is more common, such as nights, weekends, and holidays. A police officer will stop drivers using a pattern or sequence – for example, stopping every fourth car. The officers then evaluate drivers of the stopped vehicle for signs of alcohol or drug impairment. Although a police officer must have probable cause to stop a vehicle, the Supreme Court ruled in 1990 that DUI checkpoints don’t require probable cause provided that certain criteria are followed. The high court decision held that the government’s interest in reducing alcohol-related injuries was sufficient to justify a “brief intrusion” of a checkpoint. 12 states do not permit DUI checkpoints and those that do often have special requirements for the police to follow.