Really?
The U.S. Supreme Court has held that stopping someone at such a roadblock does constitute a seizure of that person under the Fourth Amendment.
One “however” further and the language of the Constitution gets tangled up in the thicket of constitutional interpretation and case law. The Supreme Court could have claimed that these stops without probable cause are constitutional under the doctrine of exigent circumstances. The Court has repeatedly held that when an officer believes evidence is about to be destroyed, he can perform a search without a warrant. However, this doctrine seems only to apply to searches. Instead, it appears as though the Court used a balancing test, common in other areas of constitutional law, whereby the “minimal intrusion on individual liberties” was weighed against the need for and efficacy of roadblocks and found to be less important.
And you say you’re all for protecting civil liberties.
The Court’s justification for the exception rested on the assumption that DUI roadblocks are necessary and effective. However, there is some controversy as to whether this is true. The National Highway Traffic and Safety Administration (NHTSA) recently released data on alcohol-related deaths in 2003 and 2004. There was a decline in such fatalities in 2004, and most of the drop occurred in states that don’t use sobriety checkpoints. Critics already concerned about the large outlay of resources required to operate checkpoints are doubly concerned if spending the resources does not even necessarily prevent DUI offenses.
So these things waste both time and resources, fail to accomplish the intended outcome, and violate the 4th amendment, but some of you still want to keep them.
The above quotes are from http://ezinearticles.com/?Are-Sobriety-Checkpoints-Legal?&id=177292