I would guess the year was 2000-2002 based on who I worked with, but I remember reading and telling a coworker:
At any given time, the average percentage of truck drivers currently on the road with enough drugs in their systems to be labeled impaired is 42%.
It would not surprise me in the least to learn that over half the drivers in the USA are doped up in one way or another. Another half is texting. Defensive driving is important!