"Some people worry that legalizing marijuana would cause an increase in car accidents by “stoned drivers”, who, like drunk drivers, have impaired reflexes and poor judgment, and indeed there is a small but real problem of marijuana-induced car accidents. But Chaloukpa and Laixuthai (1994) crunch the numbers and find that decreased price/increased availability of marijuana is actually associated with decreased car accidents, probably because marijuana is substituting for alcohol in the “have impairing substances and then go driving” population. This finding – that marijuana and alcohol substitute for each other – has been spotted again and again. Anderson & Rees (2013) find that states that legalize medical marijuana see a 5% drop in beer sales. There are however a few dissenting opinions: Cameron & Williams (2001), in complex econometric simulations that may or may not resemble the real world in any respect, find that increasing the price of alcohol increases marijuana use, but increasing the price of marijuana does not affect alcohol use, and the same researcher finds that banning alcohol on a college campus also decreases marijuana use. Also, possibly marijuana use increases smoking? This whole area is confusing, but I am most sympathetic to to the Andersen and Rees statistics which say that medical marijuana states are associated with 13% fewer traffic fatalities."
You can find the whole article here:
http://slatestarcodex.com/2014/01/05/marijuana-much-more-than-you-wanted-to-know/The part I quoted and which contains active links to the studies cited is in section III, paragraph 9.
The author really isn't for or against marijuana legalization from what I can read, he presents a fairly balanced blog post citing a lot of sources showing possible pros and cons. This blogger seems to have a fairly erudite readership so the comments are always worth perusing.
More:
"So my actual conclusion is:
There is not a sufficiently obvious order-of-magnitude difference between the costs and benefits of marijuana legalization for a evidence-based utilitarian analysis of costs and benefits to inform the debate. You may return to your regularly scheduled wild speculation and shrill accusations.
But I wouldn’t say this exercise is useless. For example, it suggests that whether marijuana legalization is positive or negative on net depends almost entirely on small changes in the road traffic accident rate. This is something I’ve never heard anyone else mention, but which in retrospect should be obvious; the few debatable health effects and the couple of people given short jail sentences absolutely can’t compare to the potential for thousands more (or fewer) traffic accidents which leave people permanently dead.
So my actual actual conclusion is:
We should probably stop caring about health effects of marijuana and about imprisonment for marijuana-related offenses, and concentrate all of our research and political energy on how marijuana affects driving."
This was written in January 2014 so it doesn't have any evidence based research later than that.
