Driving Under the Influence of Alcohol and Marijuana: Beliefs and Behaviors, United States, 2013-2015

Background

Increasing numbers of states have legalized or are considering legalizing medical and/or recreational marijuana use, bringing attention to the issue of marijuana and other drug and alcohol impaired driving among traffic safety professionals

Objective

The purpose of this study was to provide estimates of the prevalence of self-reported use and driving under the influence of alcohol and marijuana, and related perceptions and beliefs among drivers 18 and older in the United States, and to present an analysis of changes in these behaviors between 2013 and 2015

Methods

• The Traffic Safety Culture Index (TSCI) is an annual survey administered online to a sample of U.S. residents enrolled in a research panel recruited using random-digit dial and address-based sampling methods and designed to be representative of the United States population
  • For this study, 6,612 respondents were included from surveys conducted in 2013-2015
• The TSCI includes a core series of questions pertaining to the respondent’s attitudes about traffic safety, perceptions of social norms, and self-reported driving behavior. Relevant to the current study, the core survey includes questions regarding:
  • frequency of drinking alcohol and using marijuana
  • driving under the influence of alcohol and/or marijuana
  • related beliefs and perceptions, and support for countermeasures designed to address alcohol- and marijuana-involved driving
• Example question:
• “In the past year, how often have you driven…”
  • “when you thought your alcohol level might have been close to or possibly over the legal limit?”
  • “within 1 hour of using marijuana?”
  • “within one hour of consuming both marijuana and alcohol, even if you weren’t drunk?”

Key Findings

Alcohol and marijuana use

• Nearly two in three drivers (66.3%) reported that they drink alcohol at least occasionally; this percentage was relatively stable over the study period. One in ten drivers (10.0%) reported having used marijuana at least once in the past year; there was some year-to-year fluctuation in this percentage, but no evidence of a trend

Driving under the influence of alcohol or marijuana

• An estimated 14.0 percent of drivers drove with a BAC close to or over the legal limit in the past year, and 4.6 percent drove within an hour of using marijuana
• Drivers who were aged 25-39, male, and those who reported using marijuana were the most likely to report having driven with a BAC close to or over the legal limit. Drivers who were aged 18-24, male, and those who lived in the Midwest were the most likely to report having driven within an hour of using marijuana

Knowledge of per se laws for marijuana

• Awareness of per se DUI laws for marijuana was low: in states that did have a per se law, only 48.5 percent were aware of it; in states without a per se law, 44.7 percent indicated incorrectly that their state had such a law. Irrespective of whether their state actually had a per se law for marijuana, more than half of all drivers reported that they did not know whether their state had such a law
• While self-reported driving after using marijuana was not associated with actual state per se laws regarding marijuana and driving, it was significantly associated with what people thought their states’ laws were

Beliefs about effect of marijuana on driving

• Drivers are divided with regard to their perceptions of the effect of using marijuana an hour prior to driving on one’s risk of causing a crash: 58.3 percent believe this risk is increased, 6.2 percent believe it is not affected, 3.6 percent believe it is decreased, and 31.8 percent indicated that they do not know how using marijuana an hour before driving affects crash risk
• Drivers who reported using marijuana, and those who reported driving within an hour of use in the past year were less likely to believe that using marijuana increases crash risk, and more likely to believe that such use does not affect or decreases crash risk

Acceptance of impaired driving

• Virtually all drivers feel it is unacceptable to drive when one may have had too much to drink and after using both marijuana and alcohol; nearly one in ten feels it is acceptable to drive one hour after using marijuana

Support for impaired driving countermeasures

• A majority of drivers support reducing the BAC limit from 0.08 to 0.05 grams per deciliter and support having a per se law for marijuana