So in 25 years as a driver you've seen 3 or 4 instances of people quitting over a drug test. That doesn't prove anything, but it certainly suggests there wasn't a drug "problem" at your employer(s).

How many drivers got behind the wheel of a rig during that time while they were drinking or drunk? Funny how everybody is harping about weed and opium and meth but conveniently avoid mention of the the LEGAL drug that's killed hundreds of thousands of people on the highway over the years.

Cheers!