Alcohol-impaired driving in US counties, 2002–2012

In 2014, motor vehicle crashes (MVCs) remained the leading cause of death for people age 16–24 and among all age groups caused approximately 2 million injuries [1]. In 2015, over 35,000 people lost their life in a MVC in the United States, representing the largest percentage year-over-year increase (7.2%) in fatalities since 1966 [2].

Aside from vehicle speed, the most significant and measureable risk factor for involvement in, and harm from, MVCs is alcohol-impaired driving (AID) [3]. In the US, alcohol impairment is involved in roughly one-third of all MVC fatalities [4] and is an independent risk factor for increased severity of motor collision injuries [5]. Recent estimates for annual costs associated with motor vehicle crashes involving alcohol are approximately $44 billion [6].

Alcohol-impaired driving has been a serious public health problem for decades [4, 7]. Despite previous estimates of over 100 million annual episodes of alcohol-impaired driving nationwide, only approximately 1.1 million arrests were made for driving under the influence (DUI) in 2014 [8, 9]. Although previous reports on alcohol-impaired driving provide national- and state-based estimates, considerable injury prevention and traffic enforcement occur at the municipal level; thus, county-level information is useful to help guide allocation of limited public health resources and to support targeted injury prevention efforts. Using data from the Behavioral Risk Factor Surveillance System (BRFSS), we sought to estimate the county-level annual prevalence of alcohol-impaired driving in every US county for the years 2002 through 2012.

From 2002 to 2012, binge drinking episodes increased nationally from an estimated 1,703,955,652 annual episodes to 1,927,818,363 annual episodes, respectively, an 13.1% change. Respondents who reported binge-drinking behavior were more likely to engage in alcohol-impaired driving compared to drinkers who do not binge (relative risk 11.0, 95% confidence interval [CI], 9.9–12.2).

During the years in which the BRFSS asked respondents about alcohol-impaired driving (2002, 2004, 2006, 2008, 2010, 2012) there were an estimated 851,902,397 episodes of reported alcohol-impaired driving in the US. Using the annual mean from these biennial estimates, that equates to approximately 1,561,821,061 total reported episodes of alcohol-impaired driving during the study period, 2002–2012.

In 2002, there were an estimated 156,963,735 reported episodes of alcohol-impaired driving; in 2012, there were an estimated 129,652,146 reported episodes of alcohol-impaired driving, a change of − 17.4% (Fig. 1). In 2002, the age-standardized prevalence of alcohol-impaired driving in the US was 3.8% (95% UI, 3.7–4.0), compared to 3.7% (95% UI, 3.5%–3.8%) in 2012. Men were more likely to engage in alcohol-impaired driving than women; in 2012, men had 102.6 million episodes of alcohol-impaired driving compared to 27.1 million episodes among women (879 episodes per 1000 adult males versus 219 episodes per 1000 adult females).

Impaired driving among under age (< 21 years old) adults has decreased substantially since 2002. Among males, in 2002, the 18–20 year old population accounted for 14,848,467 reported episodes (2447 episodes/1000 population) of alcohol-impaired driving compared to 5,836,464 reported episodes (764 episodes/1000 population) in 2012, a 60.7% decline; among females, in 2002, the 18–20 year old population accounted for 2,656,167 reported episodes (503 episodes/1000 population) of alcohol-impaired driving compared to 1,378,562 (195 episodes/1000 population) in 2012, a 48.1% decline.

There is considerable variation in the prevalence of alcohol-impaired driving at the county level (Fig. 2). In 2012, among US counties, the prevalence of alcohol-impaired driving ranged from 2.0% in the Sitka City Borough of Alaska to 9.3% in Nance County, Nebraska. Clusters of increased alcohol-impaired driving were observed in Northern Wisconsin (Marinette, Florence, Forest, Vilas, Oneida, Iron counties), North Dakota (Cavalier, Pembina, Walsh, Ramsey, Nelson, Benson, Eddy counties) and Montana (Sheridan, Daniels, Roosevelt, Valley, Phillips, Petroleum,Garfield counties) (Fig. 2).

We also examined the prevalence of alcohol-impaired driving in the 50 most populous US counties (Fig. 3).

Among the 50 most populous US counties, Kings County, New York, had the lowest prevalence of alcohol-impaired driving (prevalence 2.0%, 95% UI, 1.5%–2.7%). The lowest prevalence counties that were not within boroughs of New York City were Salt Lake County, Utah (prevalence 2.4%, 95% UI 2.0%–2.9%) and Fairfax County, Virginia (prevalence 2.7%, 95% UI 2.1%–3.4%). Among the 50 most populous US counties, the county with the highest prevalence of alcohol-impaired drivers was Milwaukee County, Wisconsin (prevalence 5.5%, 95% UI, 4.6%–6.6%), followed by Honolulu County, Hawaii (prevalence 5.1%, 95% UI, 4.1%–6.3%).

This study found guarded progress with respect to the number of episodes of reported alcohol-impaired driving in the US from 2002–2012. However, while the age-standardized prevalence of this behavior has decreased slightly, there continues to be several million episodes of alcohol-impaired driving each month. Our findings call for renewed efforts to decrease episodes of alcohol-impaired driving in order to reduce mortality and morbidity from motor vehicle crashes.

Our results likely represent the tip of the iceberg with respect to the true prevalence of alcohol-impaired driving, as the data presented here rely on self-reported behavior, which in this circumstance is subject to social desirability bias and legal issues. Indeed, because people may not report a criminal behavior during a telephone survey, what is reported here likely represents a significant underestimate of the true prevalence of alcohol-impaired driving.

Excessive consumption of alcohol has several adverse effects on health, including increased risk for cardiovascular diseases, cancers, violence, traumatic injury, liver disease and more [18‐25]. Our study revealed persistently high levels of alcohol-impaired driving in the US. This coupled with the health danger of heavy drinking underscores the need for refocused efforts to reduce excessive drinking and alcohol-impaired driving. Indeed, the US would greatly benefit from a renewed, comprehensive approach to mitigate excessive alcohol use and impaired driving. Such an approach would need to involve improved screening, prevention, and treatment from health care workers, in addition to enhanced efforts from public health officials, city, state, and federal governments, law enforcement and, commercial enterprises focused on transportation.

Physicians can play a role in mitigating this high-risk health behavior. The United States Preventive Services Task Force recommends screening patients for risky drinking behaviors and, for those screening positive, to provide evidence-based, brief behavioral counseling interventions [26]. Such counseling may indirectly decrease the risk of alcohol-impaired driving; indeed, over 80% of reported alcohol-impaired driving episodes were reported by people who engage in binge drinking [8, 27]. Physicians can also help protect those put at risk by alcohol-impaired drivers, for example by counseling patients about the importance of safety restraint devices, such as car seats for children and 100% compliance with seatbelt utilization [28].

Physicians can also play a role in reducing subsequent harmful behavior from alcohol in the hospital setting, following an alcohol-related traumatic injury. The American College of Surgeons, which develop mandates for US trauma centers, requires that Level I trauma centers have adequate resources to both identify problem drinkers and provide behavioral interventions when possible [29]. These interventions, and the training underlying them, have been found to be both beneficial to patients and to providers [30, 31].

Despite the scope of this public health problem, there are reasons to believe improvements can be made through focused efforts by city, state, and federal governments. Indeed, in light of recent spikes in motor vehicle fatalities, there is renewed focus on preventive measures to reduce and eliminate motor vehicle crash fatalities. The clearest manifestation of these recent efforts in the US is the launch of Road to Zero, a multi-agency federal initiative whose goal is to minimize mortality from motor vehicle crashes and eliminate it completely by 2046 [32].

Other advanced countries, including those with large geographic landmass, have shown the ability to reduce mortality from motor vehicle crashes, including from alcohol-impaired driving [3]. Several countries employ best-practices, for instance alcohol-impaired driving laws based on blood alcohol content (BAC) limits less than or equal to 0.05 g/dl [33]; in the US, transportation-related federal funding remains tied to BAC limits of 0.08 g/dl [34].

Other governmental best practices may specifically target younger, novice drivers, who have an increased risk of crashing when impaired by alcohol compared to more experienced drivers [35]. These measures include graduated licensing laws, whereby novice drivers acquire increasing driving privileges over time, as well as a reduction of the BAC limit for novice drivers to 0.02 g/dl or zero [36]. Both of these interventions have been shown to reduce the risk of crash and death from alcohol-impaired driving, yet each has limited adoption nationwide. Other potential ways for local jurisdictions to reduce excessive alcohol consumption is by reducing the density of alcohol outlets at the neighborhood level [37, 38].

Technologies that enable transportation alternatives (i.e., ridesharing platforms such as Uber Technologies and Lyft) theoretically hold promise for reducing fatalities from alcohol-impaired driving, however the most comprehensive study to date found no significant effect on fatality rates in markets where these services exist [39]. As these services expand and mature, it remains to be seen if they have the ability to significantly reduce the number of alcohol-impaired driving episodes or impact fatality rates.

There are several limitations to this study. First, BRFSS data are based on self-reports, and in our case we may have underestimated the true rates of alcohol consumption and driving while impaired. Second, the BRFSS is a cross sectional study and therefore we are unable to determine causation. Third, BRFSS response rates (similar to most public surveys) have been falling, leaving open the possibility that non-response could affect our results. The BRFSS has, however, been shown to provide reliable and valid estimates in the context of declining response rates [40]. Moreover, the BRFSS is based on a large sample size and a standard methodology that allows comparability across geographic areas and time.

From 2002 to 2012, guarded progress occurred with respect to the annual number of reported alcohol-impaired driving episodes in the US. However, there continues to be several million episodes of alcohol-impaired driving each month, with notable clusters of high-risk counties located in the Middle West and Great Plains regions of the US. Because these data rely on self-reporting, this likely represents a significant underestimate of the true prevalence of alcohol-impaired driving in the United States. As levels of alcohol-impaired driving remain persistently high, renewed focus is needed to mitigate this high-risk health behavior.