The Michigan Impaired Driving Safety Commission was created and given the task of conducting research in order to recommend a scientifically supported threshold of △9-THC. This threshold, much like the .08 blood alcohol level threshold, would indicate to Michigan police whether or not a cannabis user is considered impaired while driving.
Similar studies have been done nationwide with varying results, yet most were unable to come to an absolute threshold that indicates impairment. A 2017 study involving driving simulators and instrumented vehicles revealed that cannabis-impaired subjects typically drive slower, keep greater following distances, and take fewer risks while driving than when driving sober (Compton, 2017). It was believed during this study that this behavior was due to drivers attempting to overcompensate for the subjective effects of using cannabis. In comparison, a 2013 report found an estimated 26% increase in crash risk when the driver had used cannabis (Elvik, 2013); in 2012 a study concluded ingesting cannabis increased the risk of a crash by a factor of 1 to 3 (Schulze et al., 2012); and in 2017 the National Academies of Sciences concluded that there was no substantial evidence of a statistical association between cannabis use and increased risk of a vehicle crash but that there was an increased risk of about 22%-36%.
A percentage of added risk is not enough to determine a specific threshold of THC in the system that would render a driver impaired. This threshold has been difficult to pin down due to how △9-THC is processed through the body. While THC in one’s system goes through a rapid elimination process once ingested the effects on the central nervous system are often delayed. This creates a window of time where the user may not feel the full effect of ingesting cannabis yet the levels of THC in their system are already starting to lower. A test in 2005 showed that 20 minutes after smoking cannabis the user’s △9-THC blood levels were significantly lower than when tested right after smoking (Papafotiou et al., 2005).
The Safety Commission concluded that there is no scientifically supported threshold of THC that would directly indicate a driver is impaired. Therefore, the Commission recommends the State of Michigan to utilize roadside sobriety test(s) to determine whether a driver is impaired by cannabis instead of blood tests.
If you are facing a criminal charge for driving under the influence of marijuana call Michigan Cannabis Lawyers at 517-512-8364.