Marijuana and Driving
In a study from The Orange County Crime Lab with nearly 5000 drivers suspected of driving under the influence of drugs there was no correlation of tests on psychomotor performance and THC blood concentrations.
Much has been bandied about in the press and legislatures about a AAA report showing an increase in traffic fatalities in WA and CO post-legalization. What is not often reported is:
• The number of fatal crashes in Washington increased only about 6%, from 401 to 429, between 2013 and 2014, according to FARS data. Note that 2013 had a low number of fatal crashes, "involving recent use of marijuana," compared to 2012 (409) and 2011 (421). Colorado saw a 4% increase in fatal crashes between 2013 and 2014, according to FARS.
• The AAA study acknowledges that the "recent" marijuana use detected in crash victims in Washington could have happened a week earlier, and that "the data available cannot be used to assess whether a given driver was actually impaired, and examination of fault in individual crashes was beyond the scope of this study." The increase could simply have been a result of increased prevalence of use, or increased scrutiny. The presence of blood levels as low as 1 ng/ml, in passengers and in drivers not at fault, were enough to designate a fatal crash as involving marijuana.
• The percentage of fatal crashes involving marijuana, or marijuana only, was quite low. Most fatal crashes also involved alcohol, and/or other drugs:
According to the Washington Traffic Safety Commission, of 592 drivers involved in fatal crashes in 2013, 38 tested positive for cannabis. In the following year, of 619 deadly crashes, the number testing positive for cannabis jumped to 75. However, as Staci Hoff, Research Director for WTSC, explained:
“Most of these drivers, these 75 drivers, also had alcohol or other drugs” in their systems. Over a five-year period, just 1.8 percent of fatal crashes involved drivers who tested positive only for cannabis.
“So, in our study, we looked at all five years of date, 2010 to 2014,” Hoff continued, “and there were never 3,000 drivers involved in these fatal crashes during that time period. Only 56 of them had THC and only THC, nothing else.”
• Impairment testing is the best answer and the only fair way to judge a driver. Testimony on the oral swab testing bill from law enforcement in California noted that DREs are expensive to train and deploy, but that the state would qualify for federal grants for that as-yet-unproven testing technology.
Read the AAA study
July 27, 2010 - A a careful review of the scientific evidence shows that fears about marijuana’s impact on road safety are unwarranted. There is no good scientific evidence that drug testing improves workplace safety.