Copy/paste from Wikipedia:
The Fourth Amendment to the United States Constitution states that: “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” Thus the Constitution would appear to prohibit people from being stopped without a search warrant or at least without probable cause that they have committed a crime.
The Michigan Supreme Court had found sobriety roadblocks to be a violation of the Fourth Amendment. However, in a 6-3 decision, the United States Supreme Court found properly conducted sobriety checkpoints to be constitutional. Michigan Department of State Police vs. Sitz (1990) Although acknowledging that such checkpoints infringed on a constitutional right, Chief Justice Rehnquist argued that the state interest in reducing drunk driving outweighed this minor infringement.
Dissenting justices argued that the Constitution doesn’t provide exceptions. “That stopping every car might make it easier to prevent drunken driving … is an insufficient justification for abandoning the requirement of individualized suspicion”, dissenting Justice Brennan insisted.
Chief Justice Rehnquist argued that an exception was justified because sobriety roadblocks were effective and necessary. On the other hand, dissenting Justice Stevens countered that “the findings of the trial court, based on an extensive record and affirmed by the Michigan Court of Appeals, indicate that the net effect of sobriety checkpoints on traffic safety is infinitesimal and possibly negative.” And even if roadblocks were effective, the fact that they work wouldn’t justify violating individuals’ constitutional rights, some justices argued.
Although the U.S. Supreme Court has found sobriety checkpoints to be constitutionally permissible, eleven states have found that sobriety roadblocks violate their own state constitutions or have outlawed them.[1]
The matter is often hotly argued, with some reporting that roving patrols are the more effective way to identify impaired drivers. The National Highway Traffic Safety Administration, after extensive field studies, concluded that “the number of DWI arrests made by the roving patrol program was nearly three times the average number of DWI arrests made by the checkpoint programs”.
While the supreme court does in fact admit that these checkpoints DO violate the 4th amendment, the majority opinion was that “state interest in reducing drunk driving outweighed this minor infringement.” Nowhere does it say anything about writing tickets. IMHO, the supreme court got this one wrong (Just like they got Kelo wrong).
I also find it interesting that the NHTSA study confirms what i had said, that roving patrols are much more effective at finding impaired drivers (without infringing on 4th amendment rights).