even if those drivers use the drug in their off-hours and live in states where it’s legal.

I've said this often enough:

News Scientist reported on research that revealed the probaility that 7 days after imbibing cannabis there is a peak of aggression. Just the thing you want for drivers, particularly trucks. Maybe NHTSA has read the same reports.

My impression from colleagues & acquaintances is that it is a withdrawal symptom that is a stress. Aggressive people are aggressive. Paranoic folks are paranoic. I have observed both in known users.

And a friend did explain her hubby got so bad at 5 days she got him some more and at day 12 (7 day gap) it re-surfaced, he is a lorry driver. She had to give it up personally because the railway authority she worked for tested regularly and it can be detected 1 month later. She was an emergency rail traffic controller!