Back in the day before cops all had breathalyzers they used to give field sobriety tests. Different people become impaired at different levels anyway, so why not test directly to see if they are impaired or not?
field sobriety tests.
Had one once, going through one of the gates at Elmendorf AFB about 4am. Only time I ever went through that gate stone cold sober; failed it. SSGT was perplexed that he couldn’t get any reading on his portable detector.
A buddy woke me up and insisted I go help him find his van. Assured me that he wouldn’t drive back; just wanted to know where it was. He kept falling asleep on me so I went back, still dead tired. Guess we looked suspicious at the gate....