Are Legal Limits for Marijuana Level Impairment Reliable?

The number of fatal car crashes involving marijuana use doubled in the state of Washington after the use of recreational marijuana was legalized.  One of the difficulties the state has encountered in preventing such crashes is determining per se limits for the amount of marijuana drivers can have in their systems.  Unlike alcohol impairment, which is defined by a blood alcohol content (BAC) level of .08 or higher, marijuana impairment is difficult to quantify. There is no reliable data showing that drivers become impaired at a specific level of marijuana content. Frequent users of marijuana, for example, may maintain higher levels of the drug for a longer period of time then occasional users. Thus, depending on the individual, drivers with relatively high levels of marijuana in their system might not be impaired, while others with low levels may be unsafe behind the wheel.  While there is no clear indication that a certain level of THC definitively increases the risk of car crashes, some states have implemented per se limits ranging from 1 ng/mL of THC to 5 ng/mL.

The AAA Foundation for Traffic Safety, however, is urging states to implement more comprehensive enforcement measures to improve road safety.  It suggests that, rather than relying on arbitrary legal limits, states should use a two-component system that requires (1) a positive test for recent marijuana use and, more importantly, (2) behavioral and physiological evidence of driving impairment. Marshall Doney, AAA’s President and CEO explained: “States need consistent, strong and fair enforcement measures to ensure that the increased use of marijuana does not impact road safety.”  But to maximize road safety, all motorists are advised to avoid driving while impaired regardless of whether the use of marijuana is legal in their state.

Source: https://www.sciencedaily.com/releases/2016/05/160510103131.htm

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