I'm not sure how one might reliably assess/assert impairment for a cannabis user. Traces can last for weeks and result in positive tests (blood analysis), even if the user isn't remotely stoned at the time. Don't know whether there's a breath test nowadays that indicates use in the past n hours, which might give a better idea of likely impairment.
It's not an idea I've explored seriously in any depth, but it seems like testing for capabilities required for a specific task might be a way to go here over actual drug tests.
Thus if it's determined that people need a certain reaction time to drive safely, that could be one thing tested.
Clearly setting the levels and the particular capabilities might well be contentious, but by aligning the test(s) with what's needed for the task it's fairer and in certain ways more robust: for instance, you could be under the threshold for alcohol/cannabis but if you combine that with legal medicines that cause drowsiness or simply happen to be extremely sleep deprived, you might pass a traditional test but the combined effects would lead one to fail a capability test.
It also helps in other ways too, such as fairly treating older people - you might be a sharp 75 year old and yet come up against some age limit. This let's you continue so long as you maintain the capabilities. Then if things start to change it's clear and takes some of the awkwardness out of the discussion about whether one is still fit for a job.
Of course the risk is that people are pseudoscientific or arbitrary in setting the capabilities to a level that doesn't align. We've all seen the unrealistic hiring prerequisites that managers ask for if left to decide (must have ten years experience of XYZ!) In the wrong hands these could be used unfairly (eg setting totally unrealistic levels precisely to screen out groups they don't want).
"Several meta-analyses of multiple studies found that the risk of being involved in a crash significantly increased after marijuana use13—in a few cases, the risk doubled or more than doubled.14–16 However, a large case-control study conducted by the National Highway Traffic Safety Administration found no significant increased crash risk attributable to cannabis after controlling for drivers’ age, gender, race, and presence of alcohol."
I wonder how much marijuana actually contributes to crashes. I think people can certainly get too high to drive, but unlike alcohol which lowers inhibitions, being 'too high' could even increase inhibitions somewhat (more anxiety, paranoia), so I'd expect people too high to drive are much less likely to get behind the wheel than drunk people. I certainly buy that 0.1% BAC + marijuana is probably worse than 0.1% BAC alone, but I'm curious what a just legal limit would be in comparison to 0.08% BAC regulations. What BTHCC produces equivalent impairment to 0.08% BAC, and how does that interact with THC tolerance?
Are people who consume thc multiple times per day worse drivers than people who never consume thc, when both groups are sober? I'd imagine there is a tolerance effect where stoned frequent-users are better drivers than stoned infrequent-users.
Would be interesting to try to make a cabinet arcade-style driving game that would accurately predict actual-road driving ability. Could even be used as a tool to demonstrate the dangers of drunk driving by putting it into bars and letting people try when above the legal limit (definitely some dangers of giving people good scores when they perform well while drunk though...)
