Don’t Drive Stoned And Drunk

Balko proclaims that “Colorado’s poster boy for ‘stoned driving’ was drunk off his gourd.” Kleiman chimes in:

The involvement of alcohol is hardly surprising. Drunk driving is much more dangerous than stoned driving, and the combination is worse than either drug alone.

In a followup, Kleiman asks, “what are the actual risks of stoned driving?”:

The answer, from what seems to be a well-done case-control study, is that driving stoned is hazardous, but much less hazardous than driving drunk. (A relative risk of 1.83 – meaning that driving a mile stoned is about as risky as driving two miles sober – strongly suggests that cannabis-impaired driving is a problem, but also that it isn’t much of a problem; the relative-risk number for alcohol is over 13.) On the other hand, the same study shows that adding cannabis or other drugs to alcohol substantially worsens the odds: alcohol-and-something-else has a relative risk of 23.

Given those numbers, and the technical difficulty of identifying cannabis-impaired driving (because impairment doesn’t track cannabinoid levels in blood nearly as well as it tracks alcohol levels) I’d propose the following rule: anyone who tests positive for cannabis on a mouth swab (which detects use within the past few hours) should be considered guilty of impaired driving if that person’s BAC is detectably different from zero. All that means is that, if you’ve been toking and drinking, you need to wait as many hours as you’ve had drinks before getting behind the wheel.