The “green gold rush” shows no sign of slowing.

Most recently, New Jersey legislators reportedly announced a bill that would permit recreational marijuana. If signed into law, New Jersey would join ten other states and D.C. that currently permit recreational marijuana. More than 30 states and D.C. also permit medical marijuana programs of some kind.

But as legalization spreads, concerns about driving under the influence of marijuana continue unabated.

Today, the I.I.I. has published a report that examines the current state of the issue.

“A rocky road so far: Recreational marijuana and impaired driving” dives into the hazy questions surrounding marijuana impairment: its effects on driving abilities, how traffic safety might be impacted, and how states are grappling with the issue of “stoned driving.” (Download the report here.)

Unfortunately, there are still many unknowns when it comes to stoned driving. Marijuana impairment degrades cognitive and motor skills, of course – but marijuana-impaired driving is an evolving issue with many questions and few concrete answers. Legalization is still relatively recent. Data are still being gathered. How to understand and measure marijuana impairment are still open questions.

Do the rates of marijuana-impaired driving increase following recreational legalization? Answer: probably. Does marijuana-impaired driving increase crash risks? Answer: probably, but we still don’t concretely know to what degree. What about traffic fatalities – do those increase after legalization? There’s evidence that traffic fatalities could increase following legalization, but there is still quite a bit of discussion about this issue.

There is active research, discussion and debate being conducted to answer these and other questions. As more states legalize recreational marijuana, forthcoming answers will become ever more critical to help best guide public policy and traffic safety initiatives.

To learn more, download the report here.