Two economists recently researched traffic fatalities in states that permit medical marijuana and found that traffic fatalities fell between 1990 and 2009 when pot was legalized in those states.
According to one researcher, people who drive stoned may be making roads safer since they take less-calculated risks and drive slower. Conversely, drivers who are drunk tend to take more risk and speed up.
Another theory is that stoned people don't go out into the public that much.
The study hasn't been corroborated by peer research, but the two economists -- Daniel Rees of the University of Colorado and Mark Anderson of Montana State University -- told ABC News they stand by their findings.