The Fair DUI flyer can be more effective in checkpoints than it is in a traffic stop. In a traffic stop the officer has stopped your vehicle because of reasonable suspicion that you’ve done something wrong. Typically such a stop involves a traffic violation that the officer witnessed, such as speeding or running a stop sign. Since you’ve “done something wrong,” the courts are more likely to be favorable to the police officer in this situation.
In a checkpoint, by contrast, there’s no evidence you’ve done anything wrong. While the Supreme Court allowed DUI checkpoints in Michigan v. Sitz, the opinion referenced guidelines that were followed. Many state courts have required that checkpoints be conducted pursuant to specific guidelines. Those guidelines help make the Fair DUI flyer more effective.
Because the guidelines don’t tell the police what to do when someone holds up the flyer to their window. Or more generally, they don’t indicate what they should do when someone asserts their rights.
Typically the guidelines will instruct the officers to do an initial check – perhaps a brief vehicle inspection to make sure the equipment looks proper and the license plate is valid. Then the officer is supposed to check your license, insurance and registration. If these things check out, they’re supposed to send you on your way.
However, if you admit to drinking, they smell alcohol, or if your speech is slurred, the guidelines will direct them to detain you and do a more thorough investigation.
Here’s an excerpt, probably old, from the Pima County (Arizona) guidelines:
And here are guideline suggestions from the NHTSA:
Detection and Investigation Techniques
… Officers should look for the following indicators of impairment during initial contact with a driver at a checkpoint: odor of alcoholic beverages or other drugs (marijuana, hashish, some inhalants); bloodshot eyes; alcohol containers or drug paraphernalia; fumbling fingers; slurred speech; admission of drinking or drug use; inconsistent responses; detection of alcohol by a passive alcohol sensor; etc. … Police are using the techniques taught in the SFST course to quickly detect signs of driver impairment.
Once an officer’s suspicion is raised, further investigation can take place out of the traffic lane without impeding the flow of traffic. …
Notice that some of the things they look for can only come from you opening the window and talking with them. Odors, admissions, slurred speech, inconsistent responses and “passive alcohol” detection are all things they will not be able to observe if you keep your window and your mouth shut.