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 behaviours between 2013 and 2015. The data analysed were collected via nationally-representative surveys administered during this period. From 2013-2015, 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 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. 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 or not their state had such a law. The data reported here were collected as part of the AAA Foundation’s 2013-2015 Traffic Safety Culture Index (TSCI) surveys. The TSCI is an annual survey administered online to a sample of U.S. residents ages 16 years and older who were enrolled in a research panel recruited by research firm GfK using random-digit dial and address based sampling methods and designed to be representative of the United States population. The methodology of the TSCI is described in detail in AAA Foundation for Traffic Safety (2014, 2015, 2016); the design of the panel from which the sample was drawn in described in detail in GfK (2013). 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 behaviour. Relevant to the current study, the core survey includes questions regarding respondents’ frequency of drinking alcohol and using marijuana, and questions about the respondents’ driving under the influence of alcohol and/or marijuana. The survey also includes questions regarding related beliefs and perceptions, and support for countermeasures designed to address alcohol- and marijuana-involved driving. Survey questions analysed in this study included: * “How often do you consume beer, wine, liquor, or other drinks containing alcohol?” (Responses: a few times a week, a few times a month, one or two times a month, less than once a month, never). For the purpose of this study, respondents who reported that they drank alcohol at all (more often than “never”) were classified as drinkers. * “In the past year, how often have you used marijuana?” (a few times a week, a few times a month, less than once a month, just once, never). Those who reported that they used marijuana at least once in the past year were categorized as users of marijuana. * “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?” o “within one hour of consuming both marijuana and alcohol, even if you weren’t drunk?” Response options were: regularly, fairly often, rarely, just once, never. * “In the state where you live, is it against the law for the driver to have more than a certain amount of marijuana in their system?” (yes, no, I don’t know). States were coded as having a law that makes it illegal per se (in itself) to drive with a certain amount of marijuana in one’s system, if such a law was in effect prior to each survey administration. Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Nevada, Ohio, Pennsylvania, Rhode Island, Utah, Washington, and Wisconsin had per se laws for marijuana in effect for the entire study period. Montana and Oklahoma had per se laws for marijuana become effective during the 2013 survey, thus, responses from respondents in these states were excluded in 2013 but coded as having a per se law in 2014 and 2015. Responses from respondents in North Carolina and South Dakota were excluded because they had per se laws only applicable to drivers under age 21. Responses from respondents in Colorado were excluded because the state has a specified threshold for impairment from marijuana but is not technically a per se law (Colo. Rev. Stat. Ann. § 42-4-1301 (6)). All other states were coded as not having a per se law for marijuana. * “In general, how do you think using marijuana one hour before driving affects a person’s driving?” (it makes them much more likely to cause an accident, it makes them somewhat more likely to cause an accident, it does not affect their driving, it makes them somewhat less likely to cause an accident, it makes them much less likely to cause an accident, I don’t know). *“In the United States, the legal limit for a driver’s blood alcohol concentration (a measure of the amount of alcohol in a person’s blood) is 0.08 grams of alcohol per deciliter of blood. In Australia, France, Italy, Spain, and several other countries, the limit is 0.05. How strongly do you support or oppose lowering the limit in the United States from 0.08 to 0.05?” (support strongly, support somewhat, oppose somewhat, oppose strongly). * “How strongly do you support or oppose having a law making it illegal to drive with more than a certain amount of marijuana in your system?” (support strongly, support somewhat, oppose somewhat, oppose strongly). *“How acceptable do you, personally, feel it is for a driver to…?” - “Drive when they think they may have had too much to drink” - “Drive one hour after using marijuana” - “Drive after using both marijuana and alcohol” Response options were: completely acceptable, somewhat acceptable, somewhat unacceptable, and completely unacceptable. This study is based on data from respondents age 18 and older who reported that they had driven at least once in the 30 days before they completed the questionnaire. Some questions related to marijuana use and driving were not included in the 2014 TSCI. The AAA Foundation conducted another supplemental survey in 2014 using the same sample design which included these questions (hereafter referred to as 2014 supplement). Questions about alcohol use and driving were included in the supplement so that responses to the questions about marijuana use and driving could be analysed in relation to alcohol use. Unless otherwise noted, analyses are based on data from 6,612 respondents from the 2013 TSCI, 2014 supplement, and 2015 TSCI surveys. Estimated proportions of drivers with responses of interest for each item analysed were tabulated in relation to driver demographic and other characteristics, as well as by year. Linear regression analyses were performed to test for trends by year across the study period. All analyses were performed on weighted data, all reported statistics (except sample size) are based on weighted data, and all analyses excluded non-responses. (Author/publisher)
Samenvatting