Drivers with Marijuana in their System are Less Likely to Cause Accidents than Drivers with a .05 BAC

A new comprehensive study on the effects of marijuana use and driving has demonstrated that the use of marijuana has far less impact on driving than does the use of alcohol. Despite the fact that the emerging science suggests that drivers can use marijuana and operate their vehicles safely, the DUI laws in Michigan treat marijuana as being equal to or even more dangerous than alcohol.

Part of the reason for this disparity is that the public policy behind Michigan’s DUI laws are mired in many of the archaic misapprehensions that historically existed about marijuana and its impact on driving. Now that recreational marijuana is legal in Michigan for those above 21 years of age, a rational discussion of what, if any, effect marijuana has on driving is long overdue.  To address this issue, Michael A. White and Nicholas R. Burns, preformed a meta-analysis on over 17 available marijuana studies to clarify the actual relationship between marijuana, specifically active THC, and driving.

Their study: The risk of being culpable for or involved in a road crash after using cannabis: A systematic review and meta-analyses, published in Drug Science, Policy and Law, concluded that it is likely that marijuana does not actually cause more accidents than the normal rate of accidents occurring by all drivers.  To get to this determination, they used a process called meta-analysis, which is the review of previously published studies to obtain a more comprehensive result than any single study is capable of.  For this analysis, they used 17 studies conducted between 1982 and 2020.  These studies were conducted in several countries by different researchers with differing results.  White and Burns then their own testing methodology in an effort to control for inherent biases in the prior studies.

They focused a few specific factors.  First, on whether the studies determined causation based upon marijuana use. Obviously, someone who uses marijuana can be involved in an accident that was caused by another driver.  However, several studies have failed to account for the causation of the accident and simply reported all such accidents as marijuana related, with a bias towards blaming marijuana for the accident.  Those studies were excluded.

Secondarily, White and Burns only relied on studies that specifically tested for and found THC.  Any studies that solely relied on self-reporting, chronic use, or testing result that found inactive breakdown components of marijuana were excluded from consideration.  Finally, they analyzed potential biases in who was conducting/participating in the study and how the study was conducted.

Based upon the results, White and Burns determined that the likely effect of marijuana on accidents resulted in an odds ratio of 1.0.  That ratio means that the persons who were found to have caused an accident with active THC in their system were at the same risk of accident causation as the average driver.  However, they did recognize that even if other researchers or policy makers were to disagree with their adjustments for potential biases, the odds ratio would likely only increase to 1.5. They argue that since the standard odds ratio of double the average (2.0), is often relied upon to make legal and policy decisions.

Specifically, the Australian legal alcohol limit of .05 BAC and the enforcement of speeding laws when drivers exceed 10 mph over the limit are both found to have a 2.0 odds ratio of accident causation, compared to the average driver.  This leads them to discuss the idea that the penalties of driving with marijuana are not properly related to the actual effect of marijuana on accident causation but seem more focused on punishing marijuana use compared to alcohol use or speeding.  While this is an Australian study, it is based on international data and supports a relevant discussion here in Michigan about the need to punish marijuana more harshly than other, riskier behaviors.  Instead, the decriminalization of marijuana in Michigan should be the opening to have meaningful discussions about risks it actually poses to other drivers and adjust the laws accordingly.