The Fourth Amendment to the U.S. Constitution protects people “against unreasonable searches and seizures” by police, usually by requiring them to obtain a warrant from a judge before conducting a search of a person or their property. Courts have identified some exceptions to the warrant requirement, including the “automobile exception.” Police can search a vehicle without a warrant if they have “probable cause” to believe a search will turn up evidence of criminal activity. This exception may be important to a driving while intoxicated (DWI) defense, since most cases begin with a traffic stop. A federal appellate court recently considered whether a driver’s residence in a state with legal marijuana gave police probable cause to search his vehicle. The court ruled in Vasquez v. Lewis that the search violated the driver’s Fourth Amendment rights.
Police must have “reasonable suspicion” of a criminal or motor vehicle offense before they may stop a vehicle on the road. This is a lesser standard than “probable cause.” Once police have stopped a vehicle, several exceptions to the Fourth Amendment’s search warrant requirement come into play. The “plain-view rule” states that police can search or investigate anything that they can see from outside the vehicle. An open alcohol container in a cup holder, for example, could lead to a DWI investigation, even if the officer did not suspect DWI when they initiated the traffic stop.
The automobile exception allows a much more thorough search of a vehicle, but an officer must be able to establish that evidence known to them at the time of the search gave them a good-faith belief that they would find contraband or evidence of a crime. Most exceptions to the search warrant requirement involve areas in which people do not have a “reasonable expectation of privacy,” or situations in which the risk of losing evidence makes obtaining a warrant impractical. The U.S. Supreme Court has found that both types of exceptions apply to motor vehicles, beginning with Carroll v. United States in 1925. Cars are not as private as homes, the court found, and their mobility presents an inherent risk of losing evidence.