I'd love to see documentation on that. There was actually a study done with the effects of weed and the amounts different people needed to be impaired enough to show impairment on a driving test. Some people were terrible after one dose, others were good for a few more, and an everyday smoker was fine through the total test, until they made her smoke until she was 4x the legal limit, at which point she drove fine but was driving less inhibited and more joy riding and hit a single cone. So not everyone is more likely to get in an accident from smoking. Also, remember that based upon your brain chemistry, some chemicals have different effects on people. Like someone who has a.d.d. Can take an upper and it actually calms them down, but an average person would get hyped up. In far less words, everything affects people differently and being "impaired" may or may not lead to more accidents. I can tell you that stupidity and poor motor skills are the more likely culprits in an accident than most narcotics, one of the most impairing being fully legal which is alcohol.