Drug Recognition Experts and other snake oil salesman

I saw a story on the local news yesterday where they showed a video clip of three different people all stopped for minor traffic issues and subsequently arrested for being "under the influence" (News Link). The assessment of their compromised state was made by a single policemen using an algorithm of dubious utility.

The news story focuses on a particular Officer Carroll, a decorated Cobb County Officer who is one of the approximately 250 officers in the state of Georgia who has been trained as a Drug Recognition Expert. In the three cases identified in this news story, Officer Carroll's assessment was at odds with the final laboratory evaluation, which did not demonstrate the presence of drugs. The response of the Cobb County police was nothing short of remarkable. They commented -





"Commanders would not let Officer Carroll talk with us, but they stand behind the arrests. The department doubled-down on their assertion that the drug recognition expert is better at detecting marijuana in a driver than scientific tests."

Say what? The gold standard is an poorly validated and subjective test which can be trusted over the actually measurement of a certified lab whose machines and assays use actual positive and negative controls? What drugs are these people on?