The danger of smoking and driving is real. But stoners know their tolerance much better than a biological level test ever could.
It is becoming clear that the only way to test impairment with pot is to actually test for impairment. The normal distribution of stone cold sober drivers also include people who are significantly impaired due to tiredness, stress, old age, neurological conditions, etc. A well calibrated impairment test would probably catch more sober drivers than stoned.
