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Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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4

Alcohol-Impaired Driving Interventions

INTRODUCTION

The committee’s conceptual framework for preventing alcohol-impaired driving crash fatalities was presented in Chapter 1 (see Figure 1-5). This framework illustrates the pathway from initially consuming alcohol to drinking to impairment and to driving while impaired, and shows how these actions can lead to motor vehicle crashes and the risk of serious injuries or death. Along the continuum between initial alcohol consumption and the occurrence of a fatal or serious motor vehicle crash, there are numerous opportunities for interventions that could reduce or eliminate alcohol-impaired driving incidents. This chapter examines several intervention opportunities for reducing alcohol-impaired driving, including changes in policies, laws, and enforcement; technological advances and vehicle features that could offer protections to drivers, occupants, and others; and programs or policies that could affect the sociocultural environment. These interventions offer promising approaches for improving the safety of drivers, passengers, and the public at large. A research needs section outlining gaps in the knowledge base for alcohol-impaired driving interventions is included at the end of the chapter.

POLICIES AND LAWS

A reexamination of, or modification to, existing policies and laws could provide opportunities for reducing the incidence of alcohol-impaired driving crashes. Interventions discussed in this section include

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

changes to blood alcohol concentration (BAC) laws, zero tolerance laws, graduated licensing laws, and child endangerment laws.

Blood Alcohol Concentration (BAC) Laws

Overview

Laws limiting permissible BAC among operators of motor vehicles are important interventions for reducing alcohol-impaired driving and related injuries and fatalities. Currently, in each state in the United States, drivers 21 years of age and older are prohibited from driving with a BAC that exceeds 0.08%, which is the limit proscribed in state per se laws for alcohol-impaired drivers (APIS, 2016).1 In December 2018, however, Utah will be the first state to lower its BAC per se law to 0.05%. Commercial drivers cannot exceed a BAC of 0.04%,2 and drivers under the age of 21 are restricted to a BAC varying from 0.00% to 0.02% (Fell et al., 2016; so-called zero tolerance laws, discussed later in this chapter), depending on the state where they are licensed to drive. Any individual, regardless of age or type of license, who drives with a BAC in excess of that proscribed by state law can be subject to punishments, including fines, license revocation, vehicle impoundment or restrictions, mandatory treatment, or arrest.

The following section provides information about how BAC affects the human body and an overview of the history and context of BAC laws in the United States and internationally. The section also reviews relevant scientific evidence, including laboratory and epidemiological studies of crash risk at measured BAC levels of less than 0.08%, to determine the point at which alcohol impairment occurs. Potential barriers to adopting laws lowering BAC limits and information on overcoming those barriers are also discussed. Based on its review of the evidence on the effectiveness of 0.05% BAC laws, the committee ends the section with a recommendation to state governments to lower the BAC limit set by state laws from 0.08% to 0.05%. Based on recent literature reviews and estimates by the committee and others, adoption of 0.05% per se laws nationally could save more than 1,500 lives annually (Fell and Scherer, 2017).

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1 A per se law means that the act in question is illegal and a crime.

2 For more information, see Federal Motor Carrier Safety Administration: BAC Standards. https://www.fmcsa.dot.gov/registration/commercial-drivers-license/states (accessed December 6, 2017).

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

Background

Blood alcohol (i.e., ethanol) concentration is based on the number of grams of alcohol per every 100 milliliters (1 deciliter) of blood, and it is commonly used to quantify an individual’s level of alcohol impairment or intoxication for medical or legal purposes. When an individual consumes alcohol, up to 20 percent of the alcohol is absorbed into the bloodstream from the stomach, while 80 percent or more is absorbed from the small intestine (Levine, 2006). Once alcohol is absorbed, an individual’s BAC can be measured in blood, urine, saliva, breath, perspiration, and vitreous humor, or tissues of the liver and spleen. BAC testing usually takes place at a hospital or, if a driver has been fatally injured, during an autopsy. In some cases, such as during a crash investigation or after a driver fatality, an individual’s BAC will be estimated using back (or retrograde) extrapolation, which uses a driver’s physical characteristics (sex, weight, height); absorption rate, amount, and location of alcohol in bodily tissues; and the rate of elimination to help determine an individual’s BAC when he or she was driving. Back extrapolation provides an estimate of BAC, but it is not as accurate as direct measurement from biological samples since the actual conditions under which alcohol was consumed, such as the number of drinks and time span, cannot be accounted for (Kelly and Mozayani, 2012).

After consuming alcohol, the human body undergoes multiple changes that can affect an individual’s perception and performance. Such changes include a loss of inhibition or judgment and a decrease in self-awareness, emotional stability, and coordination (Kelly and Mozayani, 2012). These deficits become more evident as the amount of alcohol ingested increases and, as a result, an individual’s ability to operate a motor vehicle safely can be negatively affected (see Chapter 1 for more details on alcohol impairment). As shown in Table 4-1, each increase in BAC is accompanied by physiological effects and inherent predictable effects on an individual’s driving capability.

Alcohol tolerance decreases the sedative effects of alcohol, making the drinker feel more alert and less intoxicated (Roehrs and Roth, n.d.; Williams and Salamy, 1972); however, tolerance has been shown to have no effect on cognitive accuracy (Schweizer and Vogel-Sprott, 2008), inhibition (Fillmore et al., 2005), executive functions (Cromer et al., 2010), short-term memory (Cromer et al., 2010), or motor impairment (García Moreno et al., 2004). In addition, the effects of alcohol tolerance can cause drinkers to underestimate the dangers of driving with a high BAC, making them think that they are not as impaired as they actually are (Amlung et al., 2014; Lapham, 2010). Similarly, mixing caffeine with alcohol has been shown to decrease awareness of impairment without decreasing the actual level of impairment (Lalanne et al., 2017; Weldy, 2010), potentially keeping a person awake longer and giving them the opportunity to drink

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

TABLE 4-1 Blood Alcohol Concentration (BAC) Levels and Physiological Effects, Effects on Driving

Blood Alcohol Concentration Typical Physiological Effects Typical Effects on Driving
0.02%
  • Some loss of judgment
  • Relaxation
  • Slight body warmth
  • Altered mood
  • Decline in visual functions (rapid tracking of a moving target)
  • Decline in ability to perform two tasks at the same time (divided attention)
0.05%
  • Exaggerated behavior
  • May have loss of small-muscle control (e.g., focusing the eyes)
  • Impaired judgment
  • Usually good feeling
  • Lowered alertness
  • Release of inhibition
  • Reduced coordination
  • Reduced ability to track moving objects
  • Difficulty steering
  • Reduced response to emergency driving situations
0.08%
  • Muscle coordination becomes poor (e.g., balance, speech, vision, reaction time, and hearing)
  • Harder to detect danger
  • Judgment, self-control, reasoning, and memory are impaired
  • Decline in ability to concentrate
  • Short-term memory loss
  • Decline in control of speed
  • Reduced information processing capability (e.g., signal detection, visual search)
  • Impaired perception
0.10%
  • Clear deterioration of reaction time and control
  • Slurred speech, poor coordination, and slowed thinking
  • Reduced ability to maintain lane position and brake appropriately
0.15%
  • Far less muscle control than normal
  • Vomiting may occur (unless this level is reached slowly or a person has developed a tolerance for alcohol)
  • Major loss of balance
  • Substantial impairment in vehicle control, attention to driving task, and in necessary visual and auditory information processing

SOURCE: Adapted from NHTSA, n.d.-a.

more alcohol and/or drive (De Sanctis et al., 2017). Typically, an alcoholic drink is defined on the basis of ethanol content in a beverage. In the United States, the standard serving size for an alcoholic drink is defined as 14 grams of ethanol or 0.6 ounces of ethanol, which is equivalent to

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×
  • 12 ounces of beer (5 percent alcohol by volume [ABV]),
  • 8 ounces of malt liquor (7 percent ABV),
  • 5 ounces of wine (12 percent ABV), or
  • 1.5 ounces or a “shot” of 80-proof (40 percent ABV) distilled spirits, such as gin, rum, vodka, or whiskey (NIAAA, 2017).

Chapter 2 provides more information on the variety of alcoholic products available on the market.

After consuming an alcoholic beverage, the absorption and elimination rates of the ethanol will determine the peak BAC. Consuming alcohol while fasting will result in a more rapid absorption of alcohol from gastric elimination, while alcohol consumed with a liquid or solid meal or while the stomach is filled will be absorbed into the body more slowly. Time to peak BAC also varies according to how much alcohol is consumed. It takes vodka (a distilled spirit) and tonic 36 minutes (±10 minutes) to reach peak BAC, wine takes 54 minutes (±14 minutes), and beer takes 62 minutes (±10 minutes) (Mitchell et al., 2014). Time to peak BAC is especially important when considering factors affecting alcohol-impaired driving since peak BAC can be reached well after a person has consumed their last alcoholic beverage but within a period of time when they may be driving a vehicle.

After ingesting alcohol, the rate of elimination from the body varies depending on the amount of alcohol and the circumstances in which it was consumed, as well as factors such as sex and weight (Wall et al., 2016) (see Figure 4-1). Approximately 90 percent of alcohol in the body is metabolized by the liver. The remaining alcohol is excreted via urine, breath, and perspiration (NHTSA, 2013a). After consuming equivalent doses of alcohol, women reach higher peak BAC levels than men (Mumenthaler et al., 1999); however, alcohol elimination per hour tends to be slightly faster among women (0.018 g/dL) than men (0.015 g/dL) (Levine, 2006; Mishra et al., 1989; NIAAA, 1999; Thomasson, 2000). One possible explanation for this disparity is that women typically have higher liver volume per unit body mass (Kwo et al., 1998; Li et al., 1998), enabling women to metabolize alcohol faster than men (Levitt et al., 1997).

Because of the relationship between BAC and impairment, law enforcement officials have used BAC measurements to estimate whether a driver’s alcohol consumption has impaired his or her capacity to drive. Of the many ways to determine an individual’s BAC, the most convenient and noninvasive—and therefore the easiest for law enforcement officials—is with a breath-testing device. The amount of alcohol (ethanol) in an individual’s breath is proportional to that in the blood; a blood alcohol reading of 0.100 g/100 mL in blood is roughly equivalent to 0.100 g/210 L in a deep-lung breath (Borkenstein et al., 1974). Police officers administer

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×
images
FIGURE 4-1 Average relationship between alcohol consumption (based on number of standard drinks and body weight) and BAC: (A) for women and (B) for men.
SOURCE: Moore and Pierce, 2016.
Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

standardized field sobriety tests or a preliminary breath test using a portable device to help determine if an individual has been driving under the influence of alcohol. If warranted, additional breath tests or testing of blood samples may be conducted at a police station or a hospital by a trained professional; the results of these tests could be admissible in a court of law (Moore and Pierce, 2016). Studies have shown that urinary ethyl glucuronide (EtG) and ethyl sulfate (EtS) biomarkers can detect recent consumption of alcohol in urine samples from 24 hours and up to 5 days after ingestion, depending on the amount of alcohol consumed (Høiseth et al., 2008, 2010; Schmitt et al., 1995; Wurst et al., 2006); however, measurements of EtG or EtS biomarkers would be unlikely to be admissible in court. Securing court-admissible test results that meet the legal requirements to be used as admissible evidence in a courtroom can sometimes be challenging (see Chapter 5).

U.S. Laws Regarding BAC

A per se law means that the act in question is illegal and a crime; with regard to impaired driving, if a driver’s BAC exceeds the limit set by state law no further proof of impairment is required, regardless of other evidence of sobriety (APIS, 2016). These laws make it easier to prosecute offenders in court if these laws are violated (LII, n.d.). In the United States, the vast majority of BAC laws fall under the jurisdiction of state courts, although an existing federal BAC per se law prohibits driving at a BAC of ≥0.08% on federal land—including, for example, military bases, national parks or forests, and court houses—and some localities have enacted local traffic codes that regulate BAC limits. Administrative license suspension (ALS) and administrative license revocation (ALR) laws authorize law enforcement officials to confiscate or revoke a driver’s license from any driver who refuses or is unable to pass a sobriety test. The suspensions or revocation occur at the time of the failed test or refusal; subsequent fines or sanctions, such as mandatory educational programs or assessment/treatment, may be levied against the offender (Chamberlain and Solomon, 2002). This is consistent with the behavioral psychology theory of deterrence, which states that laws are most effective when consequences to breaking them are delivered with certainty and celerity (Nagin, 2013). ALS/ALR laws have proven to be effective for both general and specific deterrence effects, and the laws reduce alcohol-impaired driving crashes and convictions. To date, 41 states and the District of Columbia have enacted ALS/ALR laws, which are discussed in greater detail in Chapter 5.

Rogers (1997) examined recidivism and alcohol-related crashes among driving-while-impaired (DWI) offenders in California between

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

1989 and 1991. This time period included two legal changes related to alcohol-impaired driving. The BAC per se law was reduced to 0.08% on January 1, 1990, and administrative per se (APS) pre-conviction license suspension on arrested DWI offenders was imposed on July 1, 1990. The probability of alcohol-related crash risk as well as the probability of DWI conviction 1 year subsequent to original arrest decreased among both first and repeat DWI offenders from 1989 (pre-law changes) to 1991 (post-law changes). While the contribution of lowered BAC versus the contribution of license suspension cannot be separated in the study design, in totality these results indicated that lowering BAC in conjunction with administrative and other sanctions is an effective deterrent among high-risk drivers.

The first state law penalizing drivers for driving while “under the influence of alcohol” was passed in New York State in 1920; however, prosecution of alcohol-impaired drivers was limited because law enforcement officers used behavioral observations alone to determine impairment, resulting in convictions that could be easily challenged in court (Voas and Lacey, 1990). This began to change in the 1930s with the development of breath-testing devices that could measure an individual’s BAC and the advent of laws being passed that standardized what it meant to be “impaired” (Voas and Lacey, 1990). In 1941 New York State was the first to allow a BAC of ≥0.15% (tested by breath, blood, urine, or saliva) to stand as proof of intoxication in a court of law (King and Tipperman, 1975).

Despite these early developments, decades passed before alcohol-impaired driving began to be seen as an important public health issue (Fell and Voas, 2006). In the 1970s, the National Highway Traffic Safety Administration (NHTSA) was officially established and began advocating for stricter laws and penalties for alcohol-impaired driving; soon after, Mothers Against Drunk Driving (MADD) was founded in 1980 (Fell and Voas, 2006). The efforts of these two organizations influenced the passage of many laws, including zero tolerance laws, which prohibit underage drivers from operating a vehicle after consuming any alcohol (Fell and Voas, 2006). The minimum legal drinking age of 21, which prohibits those under 21 years of age from purchasing or publicly consuming alcohol, was adopted by all states by 1988 (APIS, n.d.). Despite these successes, enacting nationwide laws focused on lowering BAC levels has been challenging.

In 1992 NHTSA released a report recommending that Congress reduce the BAC limit to 0.08% for all drivers 21 years of age and older (Snyder, 1992). In response, Congress passed the Transportation Equity Act for the 21st Century, which included $500 million of incentive grants to states enacting and enforcing a 0.08% BAC per se law (DOT, 1998). The incentives were not effective. When the act was passed in 1998, 34 states and the District of Columbia had a BAC per se law of 0.10%, and 2 years

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

later only two additional states had adopted the change (APIS, 2016). In 2000 the Community Preventive Services Task Force recommended lowering the BAC limit set by state law to 0.08%, making it clear that it was an effective public health countermeasure (Community Preventive Services Task Force, 2000). That same year the Department of Transportation Appropriations Act was passed; it specified that states that failed to pass a 0.08% per se law by 2004 would begin losing federal highway construction funds.3 With the threat of losing funds looming, more states adopted lower BAC levels. By 2004, 45 states had passed BAC 0.08% per se laws, and only 5 states remained with a BAC per se law of 0.10% (APIS, 2016). Minnesota was the last state to lower its BAC per se law to 0.08% in August 2005 (APIS, 2016).

Should BAC Laws Be Lowered in the United States?

Today, although 0.08% BAC per se laws have become widely accepted in the United States, pressure is mounting in some states to further reduce the BAC allowed by law. In 1983 Utah became the first state in the nation to pass a criminal per se law lowering the BAC limit from 0.10% to 0.08% (Chamberlain and Solomon, 2002). Now Utah is set to lead the country again with new BAC legislation. On March 23, 2017, Utah became the first state to pass a BAC per se law of 0.05%, and the bill is set to take effect on December 30, 2018 (Utah State Legislature, 2017). Currently Washington State and Hawaii are also considering similar legislation (Hawaii State Legislature, 2017; Washington State Legislature, 2017).

Several prominent organizations, such as the U.S. National Transportation Safety Board and the World Health Organization (WHO), have recommended lowering the BAC limit to 0.05% (NTSB, 2013; Peden et al., 2004). Although current BAC limits allowed by different countries for drivers range from 0.0% (in Uruguay and in many Middle Eastern countries, including Afghanistan, Egypt, and Saudi Arabia) to 0.15% (in some West African countries, including Equatorial Guinea and Guinea-Bissau), most countries have a limit of 0.05% or 0.08% (WHO, 2014). As of 2015, 34 countries—representing 2.1 billion people—had laws limiting a driver’s BAC to 0.05% or less and to 0.0% to 0.02% for young or novice drivers. These BAC limits, considered to be best practice by WHO, are imposed by many industrialized, high-income countries such as Australia, France, Germany, and Italy. Approximately 57.7 percent of countries have a national BAC limit lower than 0.08% (WHO, 2014, 2015).

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3 Department of Transportation and Related Agencies Appropriations Act of 2001, Public Law 106-346, 106th Cong. (October 23, 2000).

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

Laboratory Studies of Impairment

Researchers have used motor vehicle or motorcycle simulators in laboratory settings to measure alcohol’s effects at various BAC levels on factors such as response or reaction time, standard deviation of speed, peripheral detection, divided-attention task performance, and the ability to maintain a consistent position in a driving lane or standard deviation of lane position. Standard deviation of lane position measurements are considered one of the best indicators of impaired driving (Irwin et al., 2017). Such tests allow researchers to examine impairment and its potential effect on motor vehicle or motorcycle crashes by recreating real-world scenarios in controlled environments. Although some laboratory studies examine differences between alcohol-consuming subjects and controls, most studies examine the magnitude of impairment by measuring differences in performance measures before and after alcohol consumption in test subjects acting as their own control.

The committee reviewed a number of individual laboratory studies published since 2000 that examined alcohol consumption and subsequent driving. All of the reviewed studies were relatively small (8–40 subjects). The majority of studies used automobile simulators (Breitmeier et al., 2007; Calhoun et al., 2004; Cheng et al., 2010; Freydier et al., 2014; Friedman et al., 2011; Liu and Ho, 2010; Meskali et al., 2011; Mets et al., 2011; Parks et al., 2002; Ronen et al., 2010; Rupp et al., 2007; Tremblay et al., 2015; Verster et al., 2009); three studies were restricted to relatively inexperienced drivers and/or young adults (Freydier et al., 2014; Rudin-Brown et al., 2013; Verster et al., 2009). Examples of automobile simulator outcomes that were related to BAC levels of 0.05% or less included delayed reaction time, increased driving speed, more lane deviation, and greater inattention (Cheng et al., 2010; Freydier et al., 2014; Moskowitz et al., 2000; Parks et al., 2002). Overall the committee found consistent evidence for impairment at BAC levels of 0.05% on the basis of experimental motor vehicle driving simulator studies. Three laboratory studies used motorcycle simulator measurements for their analysis (Creaser et al., 2009; Filtness et al., 2013; Rudin-Brown et al., 2013). Outcomes adversely affected in motorcycle simulator studies at BAC levels of 0.05% or less included impaired static balance, increased standard deviation of driver position, and reduced hazard avoidance. Reaction times to visual or auditory stimuli were adversely affected in a stimuli-related study (Cheng et al., 2010).

A recent review and meta-analysis by Irwin et al. (2017) analyzed alcohol-impaired driving studies that were conducted with the use of driving simulators. After excluding studies that lacked precise performance measures, 48 different acute alcohol consumption trials—37 placebo-controlled trials and 11 trials with no control—were included in

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

the analysis. The studies estimated BAC levels measured at the start and finish of simulated driving tasks using breath-testing instruments. Meta-analysis results showed that acute alcohol consumption, as indicated by BAC levels ranging from 0.023% to 0.10%, significantly increased standard deviation of lane position and standard deviation of speed.

A report by NHTSA reviewed 112 studies published prior to 2000 that examined the effect of alcohol consumption on driving-related skills (Moskowitz and Fiorentino, 2000). The reviewed studies assessed the effect of alcohol consumption by measuring a range of BAC levels and performance on tasks in 13 categories of driving-related behaviors. Based on the studies reviewed, Moskowitz and Fiorentino (2000) concluded that, at a BAC of 0.05%, experimental studies reported significant impairment across a range of simulator outcomes related to vision, vigilance and drowsiness, psychomotor skills, attention, and information processing. Specifically, BAC levels in 27 percent of studies reported significant impairment by 0.039%, 47 percent of the studies by 0.049%, and 92 percent by 0.079%.

Laboratory studies allow for an assessment of the effects of various BAC levels on driving-related tasks in a controlled setting. To learn how these effects translate into real-world settings, however, reviewing the findings of epidemiological studies is imperative.

Epidemiological Studies of Crash Risk by BAC

Despite state laws mandating a limit of 0.08% BAC in the United States, evidence shows that a substantial proportion of alcohol-related crashes and fatalities occur when drivers have BAC levels below 0.08%. In 2015 there were 10,265 alcohol-impaired driving fatalities (BAC ≥0.08) in the United States and 1,808 fatalities involved a driver with a BAC between 0.01% and 0.07% (NHTSA, 2015). Because the presence of alcohol does not mean that crashes and related fatalities are necessarily attributable to alcohol consumption, in addition to reviewing the evidence from simulator studies (above), the committee also reviewed epidemiological studies that examined the risks of fatal crashes involving driver BACs below 0.08%. The best epidemiological evidence of the relationships between driver BAC levels and the risk of a crash are case-control studies in which BAC levels in drivers involved in crashes (cases) are compared with BAC levels in drivers not involved in crashes (controls). Case-control studies match controls with cases using drivers from the same geographic areas and ideally during the same day of the week and time of day. Some studies also obtain controls from cars traveling on the same roadways in the same direction in which case fatalities occurred. Studies conducted in the United States and abroad have consistently found an

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

increased risk of fatal crashes among drivers with BAC levels from 0.05% to 0.079% compared to having a BAC of zero (no alcohol), both overall and across a range of gender and age groups. In fact, crash risk begins to increase below 0.05%, but this chapter focuses on this range because it is a prevalent policy-related threshold in other parts of the developed world. The analyses below present a range of expected reductions in lives saved or lost at differing BAC levels owing to variations in types of implementation (i.e., sanctions, enforcement, publicity) and research methodologies.

Borkenstein et al. (1974) conducted one of the earliest case-control studies of the relationship between alcohol use and alcohol-related crashes. Crash data collected between May 1, 1959, and April 30, 1962, by the Grand Rapids (Michigan) Police Department formed the basis for the identification of control subjects who were matched to drivers involved in crashes by their proximity to the same date, time, and location of the crash. Researchers conducted four interviews with non-crash drivers at 2,000 former crash sites between July 1962 and 1963. They found that drivers with BAC levels in excess of 0.04% had an increased rate of crashes while drivers with BAC levels over 0.08% were significantly more likely to have single-vehicle crashes and crashes that were more severe and costly than those involving sober drivers. Drivers with BAC levels between 0.04% and 0.08% had a positive, steadily increasing risk of being involved in a crash.

An update to the Borkenstein et al. (1974) study was conducted by Blomberg et al. (2005). Similar in design to the study by Borkenstein et al., researchers interviewed and collected breath tests from a sample of crash and non-crash drivers from crashes of all severities that occurred in Long Beach, California, and Fort Lauderdale, Florida, during a 12-month period between June 1997 and September 1999. The final analyses of interview data collected from 4,919 crash-involved drivers (2,422 from Long Beach, 2,497 from Fort Lauderdale) and 10,066 control non-crash drivers matched to crash cases by location, day of the week, and time of day 1 week after the initial crash, found relative risks (RRs) began to increase in drivers whose BAC levels were in the range 0.05–0.06% (RR = 1.38), and those risks continued to climb with increasing BAC. The adjusted RR for drivers with a BAC of 0.06% was 1.63, 0.07% was 2.09, and 0.08% was 2.69.

Data from Blomberg et al. (2005) were reanalyzed by Peck et al. (2008) to evaluate the relationship between BAC, a driver’s age, and the risk of being in a crash. Data were evaluated according to specific age ranges—under 21, 21–24, 25–54, and 55 and older—to determine how age and a driver’s BAC affect the risk of a crash. While BAC alone was highly correlated with crash risk, Peck at al. (2008) also found that drivers under the age of 21 years had an elevated risk of being involved in a crash at all BAC levels greater than 0.0%, and those risks continued to rise with each

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

increase in BAC (e.g., a BAC of 0.05% yielded a RR of 2.75; 0.08% BAC, RR = 7.4; and 0.10% BAC, RR = 16.0). Drivers in this age group with BAC levels of 0.08% were 27.4 times more likely to be involved in a crash when compared to same-age drivers who had not been drinking (0.0% BAC). Elevated RRs were observed for drivers from all four age groups when BAC levels reached 0.05% or higher. Among drivers 21 and over the risk of being in a crash started increasing at a BAC of 0.05% (RR = 1.07), and those risks continued to increase at 0.08% (RR = 1.64) and 0.10% (RR = 2.43) but on a less steep curve than for drivers under 21.

A study of BAC and fatal crash risk was conducted by Zador (1991) and reanalyzed by Zador et al. (2000). In the original study, Zador (1991) used data from the Fatality Analysis Reporting System (FARS) collected in 1985 and 1986 and exposure data from the second National Roadside Breath-Testing Survey to analyze single-vehicle fatal crashes using drivers’ age, sex, and BAC. Researchers found that fatal crash risk increased with increasing BAC for all drivers, regardless of sex and age group (16–20, 21–24, and 25 and older). Risk of crash doubled with each 0.02% increase in a driver’s BAC above 0.0%. Drivers with BAC levels of 0.05–0.09%, regardless of age group, were nine times more likely to have a fatal crash than drivers who had a BAC of 0.0%. Male and female drivers with BAC levels between 0.05% and 0.09% had an increased risk of being killed in a single-car crash compared to comparable drivers with BAC levels ≤0.01% (RRs ranged from 9 to 54). When compared to drivers 25 years of age and older with similar BAC levels, female drivers between 16 and 21 years of age with BAC levels between 0.05% and 0.09% were at the greatest risk of dying in a single-vehicle crash (RR = 21.3); males in the same age range and with comparable BAC levels had a lower but still elevated risk (RR = 12.3).

Zador et al. (2000) updated the 1991 study using FARS data from 1996 and exposure data from the 1996 National Roadside Survey of Drivers to evaluate BAC levels in drivers of single-vehicle and two-vehicle fatal crashes. Age (16–20, 21–34, and 35 and older) and sex were evaluated in relation to BAC levels in drivers involved in crashes with fatalities. For both males and females, the fatal-crash risk was inversely proportional to the driver’s age, and increasing BAC levels consistently elevated the fatal crash risk. Contrary to the findings reported in Zador (1991), young males between 16 and 20 years of age with BAC levels between 0.05% and 0.079% had a higher likelihood of being involved in a single-car or two-car fatal crash (RR = 17.32 versus 9.94, respectively) than comparable females (RR = 7.04 versus 6.53). Among drivers 16 to 20 years of age, males had a consistently higher fatal-crash rate than females, regardless of BAC; however, these differences were not evident for drivers 21 years of age or older. Drivers between 21 and 34 years of age with BAC levels between

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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0.05% and 0.079% had a higher risk of being involved in a fatal crash than drivers 35 years of age and older. This finding was consistent for all males and females with BAC levels over 0.02%.

In 2012, Voas et al. updated the Zador et al. (2000) analysis by comparing the 1996 data to 2006 and 2007 FARS crash data (cases; n = 6,863); control blood-alcohol data were obtained from 2007 U.S. National Roadside Survey results (n = 6,823). Crash data—age, gender, type of crash (single-vehicle fatal crash versus all fatal vehicle crashes in which the driver survived), and BAC—were used to compare changes in RR between 1996 and 2007. The percentage of alcohol-impaired drivers involved in fatal crashes remained largely unchanged between 1996 and 2007 (~22 percent); assessment of gender differences indicated that underage women were increasingly at risk of alcohol-impaired driving between the two study periods, yet underage men were increasingly likely to crash even at BAC of 0.0%. Nevertheless, overall, the relative risk for being involved in a fatal crash increased steadily with increasing BAC. Among drivers 16 to 20 years of age, compared to BAC of 0.0% the relative risk of fatalities in single-vehicle crashes was 1.47, 3.84, and 12.18 at BAC levels of 0.001–0.019%, 0.02–0.049%, and 0.05–0.079%, respectively. Among all drivers, compared to BAC of 0.0%, relative risks were 1.33, 2.68, and 6.24 at BAC levels of 0.001–0.019%, 0.02–0.049%, and 0.05–0.079%, respectively. Above age 21, all age groups with a BAC of ≥0.02 were at a significantly increased risk of single-vehicle and multiple-vehicle crash fatalities. Taken together, these data indicate that BAC above 0.02%, and for underage drivers BAC above 0.001% is associated with increased crash risk in a dose-response fashion.

Lacey et al. (2016) conducted a case-control study in Virginia Beach, Virginia, that estimated how a driver’s use of alcohol, drugs, or a combination of the two contributed to crash risk. Biological samples were collected from more than 3,000 drivers from local crash scenes (cases) and 6,000 non-crash drivers (controls) matched 1 week later according to the time and location of the initial crash. Drivers were found to be 2.07 more likely to be involved in a crash if they had a BAC of 0.05% when compared to controls, and drivers who had a BAC of 0.08% were 3.93 times more likely to be involved in a crash.

More recently, Phillips and Brewer (2011) analyzed severity of crash risk by BAC among decedents in the FARS data from 1994 to 2008. The FARS codes injury severity from most to least severe as fatal injury, incapacitating injury, nonincapacitating injury, possible injury, and no injury. The ratio of serious versus nonserious driver injuries for each BAC was reported for all automobile crashes involving at least one fatality. There was a monotonic increase in the ratio of serious to nonserious injuries with increasing BAC in an involved driver. Even among those crashes with driver BAC of 0.01%, there were four times as many serious injuries

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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as nonserious, compared with three times as many serious as nonserious injuries when vehicle drivers had a BAC level of 0.0%. Inference is limited, however, given that to be in the FARS data, there had to be at least one fatality. Nevertheless, findings held true for the 14-year time period analyzed, for both single- and multiple-vehicle crashes, and after excluding the potentially confounding variables of inattention and fatigue, suggesting that BAC, even at low levels, increases not only the risk of being in a crash, but also the risk of serious injury for each crash that occurs.

With respect to BAC levels below 0.08% and the increased risk of a fatal crash, findings from U.S. studies are generally consistent with those from other developed countries. A case-control study conducted by Connor et al. (2004) in Auckland, New Zealand, evaluated the effect of alcohol consumption on vehicle crashes in which at least one occupant was seriously injured or killed. Researchers interviewed and collected breath or blood tests from 571 drivers involved in serious crashes (cases) and 588 representative drivers (controls). If those involved in the crash were unable to partake in the interview, their next of kin or a proxy was interviewed instead. After controlling for confounders, drivers with a BAC level of 0.03–0.05% were 10 times more likely to be involved in a fatal crash than drivers who did not drink. Furthermore, the researchers estimated from their models that 34 to 35 percent of fatal crashes could be eliminated if drivers with BAC levels of at least 0.03% could be prevented from driving.

Another international study by Krüger and Vollrath (2004) used data from the German Roadside Survey conducted from 1992 to 1994 (Krüger et al., 1995) and weighted those data according to a study of representative drivers to calculate the risk of alcohol-related crashes in Germany. For drivers with BAC levels between 0.05% and 0.079%, there was an increased risk of being in a crash (odds ratio [OR] = 3.6, 95 percent confidence interval [CI] 2.3–5.7).

A recent empirical nonrandomized study by Byrne et al. (2016) evaluated the deterrent effectiveness of countermeasures put in place in Ontario in 2009 and 2010 that included implementation of administrative sanctions for drivers with BAC levels between 0.05% and 0.08%. With the new administrative sanctions in place, alcohol-impaired drivers with BAC levels in this range were subject to immediate license suspensions and administrative fines, and repeat offenders could be required to attend alcohol educational classes or install an ignition interlock on their vehicle. To evaluate the effectiveness of these new sanctions, researchers analyzed data from the Ontario Ministry of Transportation’s Accident Data System and performed time series analyses. Between the time administrative sanctions were introduced and December 31, 2012, Byrne et al. estimated that the sanctions resulted in a 15 to 17 percent reduction in

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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all alcohol-related driving crashes and a 12 percent reduction in major injuries and fatalities caused by alcohol-related driving crashes.

Effect of Lowering Blood Alcohol Limits for Driving

Lowering blood alcohol limits for driving to 0.05% Although there may be increased risk of a crash at BACs above 0.05%, that does not necessarily mean that lowering the legal limit to 0.05% would reduce crashes or crash fatalities. Therefore, the committee also evaluated international studies that assessed whether or the degree to which reducing the BAC limit to 0.05% is effective in decreasing alcohol-related crashes. Overall, the majority of international evidence suggests that lowering the BAC limit to 0.05% reduces alcohol-related crashes and driving fatalities, and those effects are greatest among those groups at highest risk. An international review by Mann et al. (2001) analyzed the effect of introducing or lowering the BAC limit on traffic safety measures. A total of 27 studies conducted between 1973 and 2000 were reviewed and, of those, 13 specifically looked at countries that had reduced or introduced a BAC limit of 0.05% (Bartl and Esberger, 2000; Bernhoft and Behrensdorff, 2003; Brooks and Zaal, 1992; Desapriya and Iwase, 1996; Henstridge et al., 1997; Kloeden and McLean, 1994; McLean et al., 1995; Mercier-Guyon, 1998; Noordzij, 1977, 1994; Smith, 1986; Van Ooijen, 1977; Vingilis et al., 1988). The remainder of the studies reviewed focused on the effects of BAC levels lowered to limits other than 0.05%.

The 13 studies on the effects of introducing or reducing the BAC limit to 0.05% were epidemiological time series analyses and pre-post comparisons that examined the changes in Australia, Austria, Canada, Denmark, France, Japan, and the Netherlands. Mann and colleagues found that the studies reviewed varied in rigor and results. The pre-post comparison studies were subject to the most confounding factors, but even complex time series analyses could sometimes be influenced by confounding variables. Nevertheless, all areas that lowered the BAC limit to 0.05% or that introduced a new BAC limit of 0.05% saw reductions in alcohol-related crashes, injuries, or fatalities, although some of these effects were temporary. In South Australia decreasing the BAC limit from 0.08% to 0.05% led to a 14.1 percent reduction in the proportion of drivers with a positive BAC compared to 2 years prior (Vingilis et al., 1988). In Austria, the same reduction in the BAC limit resulted in a 0.6 percent decline in the proportion of injuries caused by alcohol-impaired driving crashes nationwide (Bartl and Esberger, 2000). The review suggests that the overall significant decreases in alcohol-impaired driving are caused by a general deterrence effect as opposed to a targeted effect on drivers with a BAC of 0.05–0.079% because reductions in crash fatalities have been observed across a range of

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

BAC levels, not just those from 0.05% to 0.079%. The jurisdictions that had the most success in reducing traffic crashes by lowering the BAC broadly publicized the new law (e.g., publicity and education) and conducted highly visible sobriety checkpoints, thereby increasing the perceived risk of being caught. Some of the reviewed studies found that the beneficial effects of the new law declined over time, which the authors posited may have been attributable to the public’s belief that, over time, the actual risk of apprehension was not as high as the perceived risk when the BAC limit was first lowered.

Albalate (2008) evaluated the effectiveness of lowering the BAC limit to 0.05% in eight European countries that changed their policies between 1991 and 2003 (Austria, Belgium, Denmark, France, Germany, Greece, Italy, and Spain), using a differences-in-differences estimation procedure in which the change in road traffic fatality rates in the country with the policy change was compared to the change in fatality rates of a control country that had not lowered its BAC. By using this approach the author was able to control for many possibly confounding variables, including socioeconomic factors such as unemployment and GDP growth rates, increasing use of motor vehicles in a country, the proportion of roads in the country that are highways and national roads, and the minimum legal drinking age. Albalate found that lowering the BAC limit to 0.05% was effective in reducing fatality rates by 4.3 percent and reducing fatality rates per kilometer driven by 6.1 percent. Among 20- to 40-year-olds, the BAC policy change reduced fatality rates by 10.5 percent, and among 40- to 50-year-olds, the BAC policy change led to an 8 percent reduction in fatality rates. No significant effect was found in females or in nonurban areas, although the authors suggested that this may be because the fatality rate among females was already low and other factors or road conditions may play a larger role in fatalities in rural areas. Among males the policy led to a 5.7 percent decrease in fatality rates and among urban males a 9.5 to 10.9 percent decrease. Lowering the BAC limit was only effective if paired with increased enforcement measures such as sobriety checkpoints. Positive effects of lowering the BAC limit were usually seen more than 2 years after the new policy went into effect.

Two recent studies evaluating the effect of lowering the BAC limit in Canada showed similar reductions in alcohol-related crashes and fatalities. Blais et al. (2015) studied the effectiveness of Canadian 0.05% administrative BAC laws by using data from the Traffic Injury Research Foundation and Statistics Canada to determine how newly instituted alcohol and driving measures may have affected alcohol-related crashes over a 24-year period. Blais and colleagues found that between 1987 and 2010, 0.05% administrative BAC laws were responsible for reducing the number of fatally injured drivers with BAC levels of 0.05% or higher by

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
×

4.1 percent (95 percent CI 0.8–7.5). A 3.5 percent reduction (95 percent CI 0.10–6.9) was also estimated in the number of fatally injured drivers with BAC levels exceeding 0.08%, and a 4.9 percent reduction (95 percent CI 1.35–8.51) was estimated in the number of fatally injured drivers with BAC levels exceeding 0.15%. Byrne et al. (2016) conducted a study in the province of Ontario to evaluate the deterrent effectiveness of new countermeasures, including lowering the BAC limit from 0.08% to 0.05%. The researchers found that the implementation of roadside suspensions for drivers with BAC levels between 0.05% and 0.08% resulted in a 17 percent decrease in injuries and fatalities related to alcohol-related crashes.

Recently, Fell and Scherer (2017) conducted a review and meta-analysis that included 36 empirical journal articles on international studies that analyzed the effects of lowering the BAC limit to 0.08% or lower. The authors calculated a pooled variance to standardize the changes observed in the different studies and determined an estimated effect size based on their results. They estimated that lowering the BAC limit from 0.08% to 0.05% in the United States would result in a decline in fatal alcohol-related crashes of 11.1 percent and save approximately 1,800 lives annually.

Lowering blood alcohol limits for driving to levels other than 0.05% (both lower and higher) The committee also reviewed evidence of the effect of laws lowering permissible BAC limits for driving to levels other than 0.05%. These studies find evidence of protective effects of lowering BAC limits to values higher and lower than 0.05%, which is important corroborating evidence that demonstrates consistency with studies where BAC limits are lowered to 0.05% specifically. Several studies provide a global perspective on the different levels of restriction that have been adopted throughout the past few decades—such as the 1990 BAC limit decrease in Sweden from 0.05% to 0.02% (Norstrom, 1997) and the 2002 BAC limit decrease in Japan from 0.05% to 0.03% (Desapriya et al., 2007; Nagata et al., 2006), both of which were effective in reducing alcohol-related driving fatalities. The evidence also finds that lowering the BAC limit from 0.10% to 0.08% for drivers in the United States was an effective policy for reducing alcohol-impaired traffic fatalities—particularly among young drivers, the age group at the highest risk for alcohol-related driving fatalities (Dee, 2001; Wagenaar et al., 2007). The majority of evidence on the effectiveness of lowering the BAC limit to levels other than 0.05% is based on time series studies and other pre-post designs that do not have a control population or quasi-experimental estimator. Of those that do, a meta-analysis shows a reduction in traffic fatalities (Wagenaar et al., 2007), but two other studies show limited effects (Freeman, 2007; Tippetts et al., 2005). Almost all available time series studies are suggestive of benefits

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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to lowering the BAC limit (Andreuccetti et al., 2011; Apsler et al., 1999; Bernat et al., 2004; Blomberg, 1992; Dee, 2001; Foss et al., 2001; Freeman, 2007; Gorman et al., 2006; Nagata et al., 2008; Norstrom, 1997; Otero and Rau, 2017; Rogers, 1995; Tippetts et al., 2005; Voas et al., 2000, 2002; Wagenaar et al., 2007). There is also variation in the size and consistency of the effect, and these variations may be related to public knowledge of the laws and enforcement (Andreuccetti et al., 2011; Bernat et al., 2004; Nakahara et al., 2013; Schwartz and Davaran, 2013; Tippetts et al., 2005).

Summary of Evidence

The available evidence can be summarized as follows. In the United States, all states currently have per se regulations that it is criminal for adults to drive with a BAC over 0.08%; lower BAC cut-points are criminal for commercial drivers and underage drivers. Yet, alcohol impairs motor vehicle operation at BACs below 0.08%, with the preponderance of experimental driving simulator evidence suggesting that BAC levels above 0.02–0.03% are associated with impairment for most people (Irwin et al., 2017; Moskowitz and Fiorentino, 2000). With regard to crash risk, the preponderance of evidence indicates that risk of crash increases monotonically with alcohol consumption, especially for underage drivers, and for all drivers at BACs beginning around 0.03% (Blomberg et al., 2005; Peck et al., 2008; Voas et al., 2012; Zador, 1991; Zador et al., 2000). Thus, the committee concludes that alcohol consumption impairs motor vehicle safety at BACs above 0.03%, and increases crash risk monotonically at this level as well.

Due to this evidence, many countries around the world have decreased the BAC limit to drive to 0.05%. This allows for an assessment of the efficacy of lowering BAC to 0.05% on driving outcomes, acknowledging that generalization from other countries to the potential experience in the United States should be done with caution. Nevertheless, the preponderance of evidence indicates that lowering the BAC limit to 0.05% significantly and substantially reduces crash and fatality risk (Albalate, 2008; Blais et al., 2015; Byrne et al., 2016; Mann et al., 2001). Importantly, crash and fatality risks are reduced not only among those drivers at or around a BAC of 0.05% or in the range 0.05–0.079%, but also at all BAC levels. This is indicative of the general deterrent effect of lowering allowable BAC to drive, or of increased awareness of impaired driving across consumption levels. The impact of lower BAC laws is observable whether enforced through administrative or criminal sanctions, and seems enhanced when introduced alongside high-visibility enforcement, sobriety checkpoints, and publicity activities (Mann et al., 2001). For the United States, Fell and Scherer (2017) estimated an 11 percent decrease in fatal alcohol-related

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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crashes, or approximately 1,800 fewer fatalities, if the BAC limit was lowered to 0.05%.

Based on the magnitude of effect and consistency of the evidence, the committee concludes that reducing the BAC limit to 0.05% is an effective strategy for reducing alcohol-impaired driving fatalities. The committee recommends BAC per se laws at 0.05% rather than another cutoff as it is the standard in many countries throughout the world, including most western countries, and thus has a solid evidence base for effective reductions in impaired driving.

Recommendation 4-1: State governments should enact per se laws for alcohol-impaired driving at 0.05% blood alcohol concentration (BAC). The federal government should incentivize this change, and other stakeholders should assist in this process. The enactment of 0.05% per se laws should be accompanied by media campaigns and robust and visible enforcement efforts.

The effectiveness of lowering the per se laws from 0.08% to 0.05% will be supported by legislation that currently applies to 0.08% per se laws, including, but not limited to, use of sobriety checkpoints, administrative license revocation, and penalties for refusing preliminary breath tests or blood tests that are equal to or greater than penalties for alcohol-impaired driving offenses. This means that the same laws and sanctions that currently apply to 0.08% per se laws could remain in place but would be enforceable at the 0.05% BAC limit. Effectiveness will also be enhanced by efforts to publicize 0.05% per se laws through mass media campaigns, by strong and sustained enforcement efforts, and through the implementation and enforcement of laws and policies to prevent illegal alcohol sales to underage or intoxicated persons (e.g., underage compliance checks with alcohol licensees, dram shop liability laws). Incentives from the federal government could include incentive grants to states or, if necessary, the threat of losing highway funding, as was done with the passage of the 0.08% per se laws. Countries with a 0.05% BAC limit implement the law through either administrative sanctions (a traffic citation with sanctions that may include insurance company notification, license suspension, and/or fines) or criminal offenses with various sanctions for drivers with a BAC between 0.05% and 0.079%. The committee offers this recommendation with the understanding that alcohol impairment and increased crash risk begin at BAC levels well below 0.08%. The primary intent of this recommendation is to reduce serious injuries and fatalities caused by alcohol-related crashes, as well as to align with other developed nations and their impaired-driver laws.

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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Potential Barriers to Adoption and Opportunities

Lowering the BAC limit in the United States from 0.08% to 0.05% will present several challenges. While many other countries have demonstrated reductions in injuries and fatalities after lowering driving BAC limits to 0.05%, variations in population characteristics, the constitutional rights of citizens, and law enforcement strategies make it difficult to draw direct correlations between experiences in those countries and potential effectiveness in the United States. There is an opportunity, however, to learn from the experiences of other countries that lowered the BAC limit and prepare for any challenges they faced. Moreover, implementation on a state-by-state basis would likely occur over time and assessments of the impacts could be conducted to inform decisions in other states.

Critics of lowering the BAC limit from 0.08% to 0.05% have argued that adoption of lower BAC limits may be onerous for police officers to enforce and could place an undue burden on the court system; however, this has not been demonstrated in studies conducted in other countries where the BAC limit has been lowered. While it is true that lowering the BAC limit to 0.05% would increase the number of drivers who fit the legal definition of being alcohol impaired, studies in other countries have shown that when the BAC limit was lowered—especially when accompanied by a well-publicized marketing campaign—there was a greater perceived risk of sanctions for drivers, which resulted in fewer alcohol-impaired drivers on the roads and a reduction in alcohol-related crashes (Albalate, 2008; Blais et al., 2015; Kloeden and McLean, 1994; Mann et al., 2001; Otero and Rau, 2017). Lowering the BAC limit also had a deterrent effect for young and new drivers, as well as drivers with no prior alcohol-related violations (Byrne et al., 2016).

Although lowering the BAC limit may result in fewer alcohol-impaired drivers on the roads, law enforcement officials would still require special training and equipment to allow them to detect impaired drivers, as is currently the case for 0.08% laws. Enforcement of a 0.05% per se law will depend on the amount of available resources for, among other things, conducting trainings, increasing police presence, and accurately conducting frequent sobriety checkpoints. It should be noted, however, that these concerns currently exist for enforcement of 0.08% laws.

Advocacy and special interest groups can have a significant effect on the public’s perception or acceptance of new public policies (Molnar et al., 2017). An example of this was seen in Utah with the passage of the first U.S. law lowering the BAC limit from 0.08% to 0.05%, which is scheduled to go into effect on December 30, 2018 (Utah State Legislature, 2017). Although a recent poll found that 51 percent of Utah residents opposed the bill, support by members of the Church of Jesus Christ of Latter-Day Saints, a group that prohibits the use of alcohol as part of their church

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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doctrine, has been credited with being instrumental for passage of the new state law (UtahPolicy.com, 2017). Despite the support that the new law received in Utah, other advocacy groups have been largely silent on the issue or have opposed it outright. MADD, arguably the most vocal proponent of reducing alcohol-impaired driving and a leading advocate in the fight to lower the BAC limit from 0.10% to 0.08%, has chosen to maintain their support of a BAC limit of 0.08% and did not support the new Utah legislation (MADD, 2017). The American Automobile Association (AAA) also has focused on other issues such as distracted, drowsy, aggressive, and impaired (defined broadly) driving (AAA, 2017). Garnering the support of MADD, AAA, and other safe driving advocacy groups would help to increase support for decreasing the BAC limit to 0.05%. Opposition to decreasing the BAC limit to 0.05% has come from distilled spirits lobbying groups, such as the American Beverage Institute (ABI). When the new BAC legislation was pending in Utah, ABI used aggressive marketing campaigns in Utah and neighboring states, and online petitions, to try to defeat the legislation (ABI, 2017a,b,c,d).

Collecting and marketing accurate information to the public is an important component of any plan to increase support for new laws lowering the BAC limit to 0.05%. As with any successful campaign, it is important for advocacy and research groups to work in concert to present a unified message and clearly counter any misleading or inaccurate information. Research into the best practices for launching, focusing, and running a successful campaign to increase support of new laws lowering BAC limits would advance the likelihood of passing new legislation and decreasing the number of alcohol-related crashes, injuries, and fatalities.

Despite the success in Utah of passing the first BAC 0.05% law and the submission of similar bills in Washington State (Washington State House of Representatives, 2017) and Hawaii (Hawaii State Legislature, 2017), support for changing U.S. laws more broadly has been lacking. Political leaders will typically act on behalf of constituents who cast their votes, and constituents have been largely silent on this issue. Alternatively, some individuals may oppose the legislation because of erroneous information such as that the law will unfairly target social drinkers or that having one drink will result in a BAC that exceeds the limit set by state law, neither of which are true (see Figure 4-1 for BAC calculation). To overcome misunderstandings among politicians and the general public, advocates for change will have to be clear and consistent with their message regarding exactly what the laws mean for drivers and the potential lives that could be saved by lowering the BAC limit across the country (Eby et al., 2017). To succeed with lowering the BAC would require a groundswell of support from grassroots organizations and voters to research and understand the issues, have access to the most credible data available from which to

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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make policy decisions, and be motivated to work on behalf of adopting strategies and legislation that can potentially save lives (see Chapter 7 on generating action for more information and a recommendation on model legislation to improve uniformity and the adoption of effective policies nationwide).

What Would It Take to Pass a 0.05% BAC Law?

The evidence reviewed by the committee suggests that lowering BAC per se laws is an effective policy in reducing alcohol-impaired driving fatalities, nonfatal injuries, and crashes. By studying the process of lowering the BAC limit from 0.10% to 0.08% in the United States, there are insights to be learned regarding what it might take to lower it further to 0.05%. Opposition against lowering the BAC per se law from 0.10% to 0.08% was strongest among the alcohol and hospitality industries and opposing legislators (Rodriguez-Iglesias et al., 2001). At that time, the main arguments in opposition to the bill were that it was unnecessary because the states already had administrative sanctions at 0.08% or that other interventions, such as increased penalties for repeat offenders, would have a greater effect on reducing alcohol-impaired driving and would not target “social” drinkers (i.e., those with BAC levels between 0.08% and 0.099%) (Rodriguez-Iglesias et al., 2001).

A study funded by NHTSA in 2001 analyzed the process of lowering the BAC per se law to 0.08% in six states, four of which had passed the law at the time of the study (Illinois, Texas, Virginia, and Washington) and two of which had not (Maryland and Minnesota) (Rodriguez-Iglesias et al., 2001). Through in-depth interviews with those involved in the process, the authors identified the following five components that were essential for getting the law passed: strong influential leadership from a key individual who is committed to the issue; the formation of strong advocacy coalitions with public and private support; bipartisan support for the bill; an effective mass media campaign; and a strong working relationship between advocates and opponents. As noted earlier, the effectiveness of lowering the per se laws to 0.05% will be supported by legislation that currently applies to 0.08% per se laws.

Laws Pertaining to Young and Inexperienced Drivers

Although motor vehicle crashes remain at the top of the list of leading causes of death for U.S. teens, the number of fatalities from crashes involving teen drivers, persons 15–20 years of age, has steadily declined from 3,490 fatalities in 2006 to 1,886 in 2015 (NHTSA, 2017a). Two laws that have been proven to be effective interventions for reducing crashes

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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and fatalities in drivers under the age of 21 are zero tolerance laws and graduated driver licensing (GDL) laws.

Zero Tolerance Laws

Zero tolerance laws, enacted in all 50 states and the District of Columbia, make it illegal for drivers under the age of 21 to drive with alcohol in their system (BAC levels in excess of 0.0–0.02%, to allow for variance in testing results). Studies of these laws have found them to be highly effective for reducing the number of young drivers who get behind the wheel after consuming alcohol (CDC, 2012; Fell et al., 2009, 2016; Haegerich et al., 2016; Liang and Huang, 2008; Shults et al., 2001).

Graduated Driver Licensing Laws

All 50 states and the District of Columbia have some form of GDL systems in place for teen drivers (CDC, 2016). These systems restrict driving privileges for teens depending on their age, the length of time they have been driving, or the time of day when they are allowed to drive a vehicle. Although specific regulations vary by state, different stages of licensure include:

  • Teens with a learners permit can only drive with a licensed, adult driver in the vehicle, and the teens may have to meet a minimum age requirement for eligibility (McCartt et al., 2010);
  • A provisional license allows a teen to drive without an adult in the vehicle, but the teen’s driving may be restricted to certain hours of the day or night or the teen may be prohibited from driving with teenage passengers in their vehicle; and
  • An unrestricted license allows a driver to drive a vehicle without time or passenger restrictions (CDC, 2016).

GDL systems have been found to be effective for reducing the number of crashes involving young, inexperienced drivers (Curry et al., 2017; Fell et al., 2011, 2016; Masten et al., 2011; McCartt et al., 2010; Salam et al., 2016; Williams et al., 2016). States with GDL systems rated as “good”—based on unsupervised driving restrictions, minimum age requirements for obtaining learners permits, and driving restrictions after licensing for a period of time or until a certain age—were associated with a 30 percent reduction in fatal crashes involving 15- to 17-year-old drivers (McCartt et al., 2010), and, although findings were not uniform for all teens, stronger GDL programs were significantly associated with a decrease in fatal crash risk for 16-year-old drivers (rate ratio = 0.74; 95 percent CI 0.65–0.84)

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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(Masten et al., 2011). In a study looking at long-term effects of the North Carolina GDL program, 16-year-old drivers who received their license under the GDL system had a lower incidence of first crashes than pre-GDL system drivers, and 16- to 17-year-old drivers’ crash incidence was 10 percent lower than comparable drivers who received their driver’s license prior to the adoption of the GDL system (Masten and Foss, 2010). The largest reductions in fatal crashes among teen drivers were seen in states with stricter nighttime driving restrictions and states that restricted new drivers to zero or one passenger for a designated period of time after receiving their driver’s license (McCartt et al., 2010).

It should be noted that many teens opt to delay obtaining a driver’s license until the age of 18, thereby exempting themselves from GDL restrictions. Some of the primary reasons cited for delaying licensure include a lack of time, money, or interest; limited or no access to a vehicle; or choosing alternate transportation options that do not require a driver’s license such as riding with friends, biking, walking, or ridesharing options; however, gender, race, and socioeconomic status have also been shown to impact the likelihood of obtaining a driver’s license (Romano et al., 2011; Schoettle and Sivak, 2013; Tefft et al., 2013, 2014). It is possible that some teens may opt to delay obtaining a driver’s license until they are beyond the age when they would be subject to GDL restrictions, but, although this could happen, studies have not identified this as a significant concern (Shoettle and Sivak, 2013; Tefft et al., 2013).

Any alcohol use by a teen driver is a serious and dangerous offense. Of the teen drivers killed in 2015, 26 percent had BAC levels of 0.01% or higher and 80 percent of those killed had BAC levels that equaled or exceeded 0.08%, the limit set by state law for drivers over the age of 21 (NHTSA, 2017a). Drinking by novice drivers over the legal drinking age is a further concern, especially since drivers over the age of 18 are not subject to the GDL restrictions and therefore can drive at any hour, without passenger restrictions. More research is needed to investigate how to restrict teen and novice drivers from getting behind the wheel after consuming alcohol. Efforts should also be made to develop strategies for restricting passengers from riding in a vehicle driven by an impaired driver, including vehicles driven by teen or novice drivers (Li et al., 2013; Walker et al., 2003).

Summary of Zero Tolerance Laws and Graduated Licensing Laws

Studies of zero tolerance and graduated licensure laws have found that the creation of high-visibility enforcement programs targeting young drivers (Johnson, 2016), increasing or strengthening existing state licensing restrictions (Williams et al., 2016), further restricting the hours when

Suggested Citation:"4 Alcohol-Impaired Driving Interventions." National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. doi: 10.17226/24951.
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young drivers can operate a motor vehicle (Curry et al., 2017; Shults and Williams, 2016), or promoting awareness of license restrictions to parents of teens (Naz and Scott-Parker, 2017) could increase the effectiveness of existing laws. More research is needed to identify how new drivers over the age of 18 fare without GDL restrictions and whether driving restrictions should be compulsory for all novice drivers. Research is also needed into further limiting alcohol-impaired driving among teens and new drivers, and strategies for preventing passengers from riding with those drivers.

DWI Child Endangerment Laws

DWI child endangerment laws target alcohol-impaired drivers who are found driving with children in their vehicles. Currently in the United States, all but three states—New Mexico, South Dakota, and Vermont—have some form of DWI child endangerment law and 42 states subject alcohol-impaired drivers to additional penalties if they are caught driving with children in their vehicle at the time of their arrest (NDAA, 2015). There is a great deal of variation between states regarding the ages of drivers and/or children who are covered by these laws, and punishments can vary from fines to community service, installation of an ignition interlock device, or imprisonment depending on details of the arrest and the state where the offense took place. Despite existing DWI child endangerment laws, children continue to be killed in crashes involving alcohol-impaired drivers. Of the 1,132 children ages 14 and younger who were killed in motor vehicle traffic crashes in 2015, 16 percent, or 181 children, were killed in alcohol-impaired driving crashes. Just over half of those children killed—92 out of 181—were passengers in vehicles driven by individuals with BAC levels that met or exceeded the limit set by state law for DWI (NHTSA, 2016a).

There is limited research regarding the efficacy of child endangerment laws as they pertain to alcohol-impaired driving, and what data exist suggest that these laws have not been effective in reducing child fatalities (Kelley-Baker and Romano, 2014, 2016; Quinlan et al., 2000; Thomas et al., 2014). Researchers have suggested that examining the effectiveness and impact of current laws, collecting and studying more granular data regarding detailed crash information and the age and gender of drivers and victims, or increasing public awareness of existing DWI child endangerment laws may lead to a greater understanding of how to increase the effectiveness of DWI child endangerment laws and eventually help to reduce the likelihood of future child fatalities in alcohol-related crashes (Kelley-Baker and Romano, 2014, 2016;