Ummm...simple logic would tell you that being stoned impairs your ability to drive.
Yes, simplistic logic tells you that. But if you read the study, they report:
“Laboratory studies have shown that cannabis use impairs driving-related functions such as distance perception, reaction time, and hand-eye coordination (Kelly et al. 2004; Sewell et al. 2009). However, neither simulator nor driving-course studies provide consistent evidence that these impairments to driving-related functions lead to an increased risk of collision (Kelly et al. 2004; Sewell et al. 2009) perhaps because drivers under the influence of tetrahydrocannabinol (THC), the primary psychoactive substance in marijuana, engage in compensatory behaviors such as reducing their velocity, avoiding risky maneuvers, and increasing their “following distances” (Kelly et al. 2004; Sewell et al. 2009).
Like marijuana, alcohol impairs driving-related functions such as reaction time and hand-eye coordination (Kelly et al. 2004; Sewell et al. 2009). Moreover, simulator and driving-course studies provide unequivocal evidence that alcohol consumption leads to an increased risk of collision (Kelly et al. 2004; Sewell et al. 2009). Even at low doses, drivers under the influence of alcohol tend to underestimate the degree to which they are impaired (MacDonald et al. 2008; Marczinski et al. 2008; Robbe and O’Hanlon 1993; Sewell et al. 2009), drive at faster speeds, and take more risks (Burian et al. 2002; Ronen et al. 2008; Sewell et al. 2009). When used in conjunction with marijuana, alcohol appears to have an “additive or even multiplicative” effect on driving-related functions (Sewell et al. 2009, p. 186), although chronic marijuana users may be less impaired by alcohol than infrequent users (Jones and Stone 1970; Marks and MacAvoy 1989; Wright and Terry 2002).4
Yet the study isn’t advocating, and concludes (with rare scientific restraint):
“However, because other mechanisms cannot be ruled out, the negative relationship between medical marijuana laws and alcohol-related traffic fatalities does not necessarily imply that driving under the influence of marijuana is safer than driving under the influence of alcohol. For instance, it is possible that legalizing medical marijuana reduces traffic fatalities through its effect on substance use in public. Alcohol is often consumed in restaurants and bars, while many states prohibit the use of medical marijuana in public.35 Even where it is not explicitly prohibited, anecdotal evidence suggests that public use of medical marijuana can be controversial.36 If marijuana consumption typically takes place at home, then designating a driver for the trip back from a restaurant or bar becomes unnecessary, and legalization could reduce traffic fatalities even if driving under the influence of marijuana is every bit as dangerous as driving under the influence of alcohol.”
"being stoned impairs your ability to drive"
For sure, it makes it a lot easier to get lost.
Dang, I spaced out and forgot to turn back there.