The National Highway Transit Safety Association (NHTSA) recently released a report to Congress outlining the research they currently have on Marijuana use and its effect on driving.  In sum, the report found that the effects marijuana have on driver’s ability to operate safely is unsettled. In fact, there is some research out there that shows that those impaired may in fact operate their vehicle in a more careful manner then when sober or under the influence of alcohol.  Here are five takeaways from this report.

1) THC levels found in blood do not equate to a level of impairment:   One of the major tools used by law enforcement is the blood draw.  This can provide concrete proof that a motorist has used marijuana in the past.  However, it is stated several times over in the report, that the science does not support a level of impairment based on the THC level alone.  In fact, low levels of THC can be found in the blood for up to 30 days after use, which makes it difficult to equate a THC level with a level of impairment.

2) Some tests have shown that those under the influence of marijuana drive more carefully then those who are sober.  An interesting study was  released in 2015 that marijuana may in fact mitigate risky driving by those under the influence of alcohol.  It further found that those under the influence of marijuana tended to drive slower and at farther distances from a vehicle in front of them.

3) Specific cues of marijuana impairment are not available to detect impairment with reasonable certainty:  NHTSA has admitted that unlike with alcohol, law enforcement cannot point to a series of standardized evidentiary cues that can per-se, lead them to a conclusion marijuana impairment.

4) Marijuana’s role in causing crashes is “less clear”:  NHTSA has admitted in their report that it is difficult to correlate the cause of crashes due to marijuana impairment.  The hurdles to show that marijuana impairment does in fact increase the risk of a crash are the same in which NHTSA acknowledged with regards to THC levels in the blood (i.e. they do not equate to a level of impairment).  Further, the presence of THC in the blood for 30 days, skews any data they may have that states that marijuana impairment was in fact the cause of the CRASH.

5) Impairment Curve of Marijuana is sudden:  With alcohol, there has long been established a BAC curve, that shows how alcohol is processed.  Customarily, a peak BAC is reached 20 minutes after the last drink has been consumed.  With marijuana, it is much more difficult to calculate.  According to NHTSA, peak impairment occurs immediately after smoking and drops significantly thereafter.  This curve is heavily dependent on the user, as those who are regular consumers may show far less signs of impairment even after consuming large doses then those who use less consistently.

The overall takeaways from this Marijuana report, is that much is still to be learned about the effects of Marijuana and driving.  Despite this significant gap in knowledge however, one thing was made crystal clear by NHTSA’s report.  They want to see more Drug Recognition Experts trained and on Vermont roads.  This, with the impending legalization bill, will likely result in an increase in Vermont DUI-Marijuana arrests, despite the evidence that supports these arrests remaining unsettled.