Americans are growing more comfortable with marijuana, with 58 percent favoring legalization, according to the latest Gallup poll. At the same time, some researchers believe they have identified a side benefit to increasing availability of the drug: It could lead to decreased consumption of alcohol among young people.

In a paper in the winter issue of the Journal of Policy Analysis and Management, two researchers — D. Mark Anderson of Montana State University and Daniel Rees of the University of Colorado at Denver — report that legalization of marijuana for medical purposes has been associated with reductions in heavy drinking, especially among 18- to 29-year-olds, and with an almost 5 percent decrease in beer sales. In addition, the increase in the legal drinking age from 18 to 21 seems to encourage greater marijuana use among people under 21, usage that drops sharply when they reach the legal drinking age.

If marijuana is widely legalized for recreational purposes (only Washington State and Colorado have taken that step), the consequences are far from clear. But assuming the argument that alcohol and marijuana are “substitutes” bears out, that could be good news, especially for road safety. Of the two substances, alcohol is far more hazardous.

For the most part, marijuana-intoxicated drivers show only modest impairments on road tests. Several studies have suggested that drivers under the influence of marijuana actually overestimate their impairment. They slow down and increase their following distance. The opposite is true of drivers under the influence of alcohol.