Studies Put Drug Chemical DWI / DUI Laws Under Scrutiny

Although some state legislatures have passed laws regulating marijuana use by motorists, a recent study by the AAA Foundation for Traffic Safety, cited by the New York Times, suggests that at least some such laws are not supported by scientific evidence. While BAC is a reasonably consistent measure of alcohol impairment, THC blood levels are not consistently indicative of impairment following marijuana use.

In response to the study, Jake Nelson, the Director of Traffic Safety Advocacy and Research at AAA, says “there is no concentration of the drug that allows us to reliably predict that someone is impaired behind the wheel the way that we can with alcohol.”


There are key reasons why legislating marijuana use by motorists is problematic. First, some users are not actually impaired. Jolene Foreman, an attorney with the Drug Policy Alliance, says that many regular users, particularly those who use marijuana, exhibit no signs of impairment. Foreman says that marijuana can remain in an individual’s bloodstream for days or even weeks after its effect on the brain wears off.

Second, the THC blood level is not a reliable predictor of impairment. The AAA study found that tested levels of THC in the blood do not reflect blood levels at the time of arrest, nor does it accurately reflect the impact of marijuana’s psychoactive ingredient on the brain.

Foreman suggests that current laws inevitably lead to arbitrary punishment. In fact, she suggests that using marijuana in the hours before driving is like having a glass of wine three nights before driving – it is not predictive of whether the driver is safe on the roads in the present.

Also, some object to current THC blood testing on the grounds that any claims regarding statistical information about THC blood concentration levels might unduly sway a jury in certain cases.


Foreman identifies two groups that are particularly vulnerable to THC testing as it now stands. First, patients using medical marijuana. They will often exhibit high levels of THC in the blood regardless of their actual sobriety. Second, minorities who may commit traffic violations at levels similar to whites even though statistics show that they are more likely to receive citations.


These scientific realities run counter to the laws in a number of states. Indeed, there is a presumption of guilt if THC blood concentrations are above a certain level in a number of states.

Ultimately, the reality that marijuana use can lead to some level of impairment in certain motorists remains. The dilemma is how to legislate the issue and identify motorists that are actually impaired.


Researchers involved in the AAA study recommend that officers administer a standard field sobriety test to those suspected of impaired driving. Then, if a motorist fails the test, a trained specialist would step in to examine numerous factors to determine if the driver is indeed impaired, The recommendations also include a provision for a blood test that only confirms the presence of THC in the blood, rather than one that presumes to establish that the amount of THC in the blood can conclusively establish impairment.


According to the New York Times article, more than 12 additional states will look at marijuana legalization in 2016, so the issue of impairment from marijuana use will become more important.

If you or a family member faces drug chemical DWI / DUI charges, please contact us for assistance. We fight hard to protect the full legal rights of our clients. We offer an initial complimentary consultation.