Advocates of medical marijuana make lots of arguments: it eases pain for the seriously ill, it brings into the open the underground black market, etc., etc.
Here's a possible new one for their arsenal -- it can reduce traffic deaths, especially those tied to drinking.
That's the conclusion of a new study that found that traffic fatalities dropped by nearly 9 percent in the 13 states, including California, which legalized medical pot between 1990 and 2009.
In their paper published by a German research center, economists D. Mark Anderson of Montana State University and Daniel I. Rees of the University of Colorado say the link between marijuana and traffic safety is beer consumption.
They suggest that the easier the access to pot, the more people are substituting marijuana for beer, especially 20- to 29-year-olds. Less drinking, particularly in bars, means less drinking and driving and fewer accidents.
That, of course, cuts both ways because it suggests that medical marijuana is being widely used recreationally -- not quite what most California voters thought they were approving when they passed Proposition 215 in 1996.
Based on a more limited sample -- Montana, Vermont and Rhode Island -- Anderson and Rees also say that the legalization of medical marijuana leads to increased consumption among adults, but not among children.
Emily Badger, writing for the Atlantic magazine's website on city issues, notes that this study could also interest those who want to reduce traffic deaths. Raising the driving age reduced deaths. So did mandatory seat-belt laws. "Policy-makers," she writes, "may now want to add to this list an unexpected intervention: Legalize medical marijuana."