i think the issue is right on the edge - and it is regularly challanged because of that. we are garaunteed to be secure against unreasonable searches under the 4th amend. so.... the question centers around wether the search and seizure was reasonable or not, ie, a balance btw needs of the state on the one hand and the protections of the 4th on the other.
the U.S. Supreme Court has upheld the use of police roadblocks for several purposes, including highway safety, protection of national borders, and the sobriety checkpoints.
Brief stops allowing most motorists to proceed in a matter of seconds, that search for only one purpose, and checkpoints that advance a valid state interest, such as safety on the highways - have all been ok'd by the supremes.
but dragnet type searches for any and all violations are unconstitutional.