BAT Mobiles are motor homes outfitted with breath testing instruments and serve as mobile police stations. They can be brought to the scene in rural areas or stationed on-site at sobriety checkpoints. The sobriety checkpoint is a highly visible enforcement mechanism. All motorists approaching a designated area of highway are stopped and briefly investigated for signs of intoxication. Its purpose is to maximize deterrence, by increasing the risk perception of motorists who drive while impaired by alcohol or drugs.
Evidence suggests that sobriety checkpoints can reduce the number of alcohol-related accidents.
The legality of these checkpoints has been challenged in the courts on the grounds they violate the Fourth Amendment prohibition against illegal search and seizure. The U.S. Supreme Court upheld their constitutionality in 1990 in the case of Michigan Department of State Police v. Sitz. The Supreme Court ruled that the Fourth Amendment does not forbid the initial stop and brief detention, without individualized suspicion, of all motorists passing through a highway checkpoint established to detect and deter drunk driving, conducted in conformity with guidelines on operation, site selection, and publicity. Despite the federal ruling, certain states have since enacted legislation or interpreted their state constitutions in such a manner as to forbid these checkpoints. These guidelines stress that checkpoints should be part of an ongoing program to deter impaired driving, should have judicial support, and should conform to department policy.