Illinois v. Lidster, some scary language
In Illinois v. Lidster, the U.S. Supreme Court held that a road-side traffic stop whose only purpose was a fishing expedition for law enforcement officials, did not violate the 4th Amendment.
The Court writes that a per se rule against information gathering checkpoints is not needed because law enforcement departments do not have the resources to monitor every intersection. (Slip Opinion at 6). In other words, a lack of money is all that protects the American citizen from tyranny.
So long to a Supreme Court that cares about individual rights.