A roadblock, also known as a sobriety checkpoint, is a temporary stop-point operated on a public road, which must be governed by established guidelines, set out by the California Supreme Court in the premiere roadblock case, Ingersoll v Palmer. A sobriety checkpoint roadblock must have advance notice to the public, set up by policymaking officials other than officers in the field, guided by a neutral mathematical formula, maintained safely for both police and motorists, have high visibility thus serving to give advance warning to the motorist as to the official nature of the stop, and minimize the average time each motorist is detained.



Each motorist stopped should be detained only long enough for the officer to question the driver briefly and to look for signs of intoxication, such as alcohol on the breath, slurred speech, and glassy or bloodshot eyes. If the driver does not display signs of impairment, he or she should be permitted to drive on without further delay. If the officer does observe signs of impairment, the driver may be directed to a separate area for a roadside sobriety test. At that point, further investigation must be based on probable cause, and general principles of detention and arrest would apply.

The United States Supreme Court has held that a vehicle stopped at a roadblock is a “seizure" under the Fourth Amendment. A Fourth Amendment seizure occurs “when there is a governmental termination of freedom of movement through means intentionally applied." The question then becomes whether such seizures are reasonable under the Fourth Amendment. It has been determined that not all roadblocks violate the Fourth Amendment right against unreasonable searches and seizures. In order to determine whether there has been a Fourth Amendment violation, courts apply a “balancing test" which balances the government’s interest against the intrusiveness of the detention on the individual. If a roadblock is operated in accordance with the required safeguards set out in Ingersoll, then there is no actionable intrusion on the Fourth Amendment. The intrusion on the individual is justified by the magnitude to society of having drunk drivers on the road. The Supreme Court has stated that the primary purpose of a sobriety check point is not to discover evidence of crime or to make arrests of drunk drivers, but to promote public safety by deterring intoxicated persons from driving and endangering the public. Thus, a sobriety checkpoint roadblock serves a regulatory purpose and is not considered a criminal investigation roadblock, and no warrant is required.