What is the "automobile exception" to the search warrant requirement?

2 Even assuming that a warrantless search occurred, it was nonetheless constitutional. The "automobile exception" to the warrant requirement obviously recognizes that the inherent mobility of an automobile "creates circumstances of such exigency that, as a practical necessity, rigorous enforcement of the warrant requirement is impossible." California v. Carney, 471 U.S. 386, 391 (1985), citing, South Dakota v. Opperman, 428 U.S. 364, 367 (1976). See also Carney, 471 U.S. at 391-92. (citations omitted).