“States that legalize medical marijuana see fewer fatal car accidents, according to a [Nov. 2011] new study in part because people may be substituting marijuana smoking for drinking alcohol…
Comparing traffic deaths over time in states with and without medical marijuana law changes, the researchers found that fatal car wrecks dropped by 9% in states that legalized medical use — which was largely attributable to a decline in drunk driving…
The authors also found that in states that legalized medical use, there was no increase in marijuana smoking by teenagers — a finding seen in other studies as well. But, in many cases, the laws were linked with an increase in marijuana smoking among adults in their 20s; this rise was accompanied by a reduction in alcohol use by college age youth, suggesting that they were smoking weed instead.”