The Fourth Amendment applies to motor vehicles. New York v. Class, 475 U.S.
106, 114-15, 106 S. Ct. 960, 89 L. Ed. 2d 81 (1986). But the Court has long recognized that government agents need not obtain a search warrant for a motor vehicle if they have probable cause to believe contraband or evidence of criminal activity may be found there.
That is, a warrantless search of a motor vehicle based on probable cause alone will be
considered reasonable under the Fourth Amendment.
The motor vehicle exception to the warrant requirement is rooted in twin considerations: the ready mobility of the vehicles and the reduced expectation of privacy their occupants and owners enjoy. The United States Supreme Court has succinctly stated the motor vehicle exception this way: "If a car is readily mobile and probable cause exists to believe it contains contraband, the Fourth Amendment thus permits police to search the vehicle without more."