In order for a traffic stop to be considered constitutional, law enforcement must have “reasonable suspicion” to pull a driver over. This very low standard requires only that an officer be able to articulate a reason for initiating the stop. Once the stop is made, “probable cause” is required in order for the officer to begin a DUI investigation.
This requirement of probable cause can be fulfilled if the officer has a reasonable belief that the driver in question has been driving drunk. If an officer must have reasonable suspicion to stop a car, and probable cause to investigate for a DUI, how do law enforcement agencies justify random sobriety checkpoints? The U.S. Supreme Court held, in Michigan v. Dept. of State Police v. Sitz, that while random checkpoints violate the 4th Amendment right against unreasonable search and seizure, the governmental interest in preventing drunk driving outweighs the minor infringement. In Ingersoll v. Palmer the California Supreme Court held that random sobriety checkpoints are considered “administrative procedures” rather than “criminal investigations.” The court further stated that, in order to be valid, sobriety checkpoints must meet specific requirements. In order to be valid, checkpoints must be publically advertised, reasonably located, and must allow approaching drivers to navigate away from the checkpoint.