I wonder where they think they get the authority to detain people to ask them to submit to voluntary tests? It doesn't sound like they held up a sign asking people to please stop and take a test. They forcibly stopped people.
This underlines the huge constitutional problem with dui/license checkpoints.
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated" seems fairly clear. Maybe the problem is that our founders did not define the term unreasonable so now our government has simply redefined reasonable to include stopping and searching everyone.