Can Sobriety Tests Weed Out Drivers Who've Smoked Too Much Weed?
npr.org
npr.org
I.e. there are so many different psychoactive substances, that effect, rather than presence, seems to be the only 'fair' way to discriminate in a world where most people take at least 1 medication a week or more.
Alcohol is probably worse.
Allowing people to research cannabis would let us know what the risk is.
(I expect it is higher, but that seems hard to produce meaningful data. Self reported? Subject to a blood test? A piss test that detects 2 months use?)