Generally, police aren't allowed to stop a vehicle unless there's reason to believe a crime or traffic violation has been committed. So how is it that police can set up a sobriety checkpoint and—without any specific evidence of drunk driving or any other crime—stop every car that comes down the road?
The Fourth Amendment to the U.S. Constitution allows only searches and seizures that are "reasonable." And when police pull over a vehicle, it's considered a seizure for Fourth Amendment purposes. Typically, a vehicle stop is reasonable only if the police have a reasonable suspicion that the driver has broken the law.
But with DUI checkpoints, police stop every car on the blocked roadway—meaning police detain these drivers without having reason to believe they did anything wrong.
In spite of the general rule, the Supreme Court has found that temporary DUI checkpoint stops (without reasonable suspicion) do not violate the Fourth Amendment rights of drivers at checkpoints. Basically, the Court said the importance of keeping impaired drivers off the road generally outweighs the inconvenience and intrusion to motorists. (Michigan Dep't of State Police v. Sitz, 496 U.S. 444 (1990).)
However, the Supreme Court's general approval of sobriety checkpoints doesn't mean every detention at such a checkpoint is lawful. For example, if police were to delay a driver for an inordinate amount of time or search the inside of a vehicle without evidence of impairment or wrongdoing, it's likely a court would find the stop went beyond what was reasonable. As with all searches and seizures, the legality of a DUI checkpoint detention depends on the circumstances.
Under the U.S. Constitution, as interpreted by the U.S. Supreme Court, DUI checkpoints are generally legal. But states have their own constitutions and statutes (laws written by state legislatures). These sometimes afford individuals greater rights with regard to interactions with law enforcement.
Several states, including Iowa and Wisconsin, have statutes that prohibit sobriety checkpoints. And in a number of other states—like Oregon, Washington, and Michigan—DUI checkpoints violate the state constitution. So, for law enforcement in these states, sobriety checkpoints aren't an option.
If you've been arrested for driving under the influence or any other crime, get in touch with a qualified attorney. State laws vary and the circumstances of every case are different. An experienced DUI lawyer can tell you how the law applies to the facts of your case and let you know if you have any defenses that might work.