Effects of Blood-Alcohol Concentration (BAC) Feedback on BAC Estimates over Time

Abstract This study examines the effects of self-tested blood alcohol concentration (BA C) feedback, from personal hand-held breathalyzers, on the accuracy of BAC estimation. Using an e-mail prompted web-based questionnaire, 19 participants were asked to report both BAC estimates and subsequently measured BAC levels over the course of 27 days. Results from the 14 subjects who reported drinking during that time period suggest that BAC estimation improves over the first four drinking events, only when controlling for amount of alcohol consumed. BAC estimate accuracy was found to decrease as number of drinks and measured BAC increased. Participants were more likely to over-estimate their BAC's than to under-estimate them but this trend was much more pronounced for light drinkers than for heavy drinkers. There were no additional effects of heavy/light drinker status on estimate accuracy, beyond the effects of BAC at time of measured event. INTRODUCTION Department of Transportation projection statistics indicate that 249,000 people were injured, and 16,645 died in alcohol-related crashes in the U.S. in 2004 (National Highway and Transportation Safety Administration [NHTSA], 2005). Although rates for these incidences have been decreasing over the past several years, the decreases are predominantly in crash rates for those with blood alcohol concentration (BAC) levels between .01 and .07. For those with BAC levels at or above .08, the decline has been minimal. Trends also show that young drivers 21-34 years of age are disproportionately represented in alcohol related crashes and represent the highest rate of driving with BAC levels above .08% (NHTSA, 2004). Although 1.5 million drivers were arrested for driving while impaired in the U.S. in 2002 (NHTSA, 2004), very few impaired drivers actually get stopped and even fewer are convicted. Only 4% of surveyed drivers aged 16-20 who reported driving impaired in 2002 and 2003 were actually stopped and booked for DUI offences (Beitel, Sharp, & Glauz, 2000). The most effective policies directed at the reduction of injury and death from drunk driving in the past several years have been those that increase the legal drinking age, increase enforcement and punishment of drunk drivers, and adopt lower per se drinking and driving BAC limits (Greenfield, 1998; Hingson, Heeren, & Winter, 1994; Mann, 2002; Nan, Van Houten, Rolider & Jonah, 1993; Robertson, Rich, & Ross, 1973; Shults et al., 2001; Voas & Holder, 1997; Wagenaar, O'Malley, & LaFond, 2001). These per se laws state that a specific amount of alcohol in the blood indicates evidence of impaired driving ability. Recent federal policies have mandated the adoption of a drinking and driving BAC limit of .08% (grams of alcohol in 100 ml of blood) for all states. In addition, all 50 states and the District of Columbia have adopted very low (.01-.02%), or zero-tolerance, limits for underage drivers (Governor's Highway Safety Association, 2003). Although epidemiological research concerning car crashes and alcohol use shows that lower limits on per se laws are effective in reducing alcohol-related injuries and deaths (Hingson, Heeren, & Winter, 1994; Shults et al., 2001; Wagenaar, O'Malley, & La Fond, 2001), the association between measured BAC and impairment is not straightforward. The amount of alcohol it takes to impair one's driving ability depends on several factors. Because BAC measures the percentage of alcohol in the bloodstream, it controls for factors that affect the absorption level of consumed alcohol such as type and timing of drinks, food consumption, body weight, sex, and individual physiological differences. Laboratory studies concerning drinking and driving impairment generally test reaction time, tracking ability, and vision loss at various BAC levels. Such studies indicate that significant impairment begins at the lowest measurable BAC and increases steadily with higher BAC's (Greenfield, 1998; Hutt, 1997; Levinthal, 2002; Mann, 2002; Moskowitz & Burns; 1990). …