Under the Influence
You notice a driver weaving in and out of traffic, so you signal with lights and siren for him to pull over. He definitely seems out of sorts, so you conduct the standardized field sobriety tests, which he fails. But when you administer a breath test, his blood alcohol content (BAC) is way below the legal limit for alcohol–despite his clearly exhibiting signs of being under the influence. What you have here is most likely a case of "drug driving."