Exactly.
That was the problem with the previous program we had, called RID, which was a form of sobriety checkpoint. The drivers always had the possibility that, even though they were pulled over, if they didn't breathe on the policeman or they could act appropriately and the policeman didn't suspect they had been drinking, they might not be breath tested. Now, in practice, I think the police are fairly good at that, but the key aim was to create the impression in the public's mind that when you are pulled over, you are highly likely to be breath tested.