Marijuana and Driving

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Cal NORML has been successfully fighting for marijuana users’ driving rights since the 1980s, when we fought off yearly attempts at zero tolerance “Smoke a Joint, Lose Your License Laws” pushed by the federal government. We recently sat on a three-year CHP task force on drug- and alcohol-impaired driving, where we have pushed against a per se standard for marijuana DUIDs while evaluating current technologies and research for roadside testing.

Read more:


Taking Drugged Driving Seriously: What Does the Science Say? 9/17

Marijuana-Impaired Driving A Report to Congress 8/17
An honest and accurate report. The poor correlation of THC concentrations in the blood with impairment is discussed, along with the implication that setting per se levels is not meaningful.

The unadjusted odds ratio for THC was 1.25, representing a significantly elevated risk of crashing by about 1.25 times or 25 percent. These unadjusted odds ratios must be interpreted with caution as they do not account for other factors that may contribute to increased crash risk. Other factors, such as demographic variables, have been shown to have a significant effect on crash risk. For example, male drivers have a higher crash rate than female drivers. Likewise, young drivers have a higher crash rate than older drivers. To the extent that these demographic variables are correlated with specific types of drug use, they may account for some of the increased crash risk associated with drug use.

Trump Administration to Study Marijuana and Driving 1/17

Study: States with Medical Marijuana Laws Have Lower Traffic Fatality Rates 12/16

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 involving marijuana 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.