Alcohol-related driving fatalities persist as a public health issue in the United States. Although the trends regarding driving under the influence (DUI) have been improving in the past few decades due to policy changes and organizations such as Mothers Against Drunk Driving (MADD), the statistics have plateaued. In 2022, there was still one death every 39  minutes due to drunk driving, which is similar to statistics calculated in 2021 (NHTSA, 2024). Studies have begun focusing on driver risk-taking as a factor in DUI occurrences and consequent driving fatalities (Barry, 1973, Laude and Fillmore, 2015, Leung and Starmer, 2005). Risky driving behavior can include speeding, tailgating, weaving in and out of traffic, and running red lights. Studies have found that intoxicated drivers are more willing to choose risky traffic lanes over less-risky options (Burian et al., 2002, Burian et al., 2003), maneuver through narrower gaps (Cohen et al., 1958), and underestimate potential collision time with oncoming traffic (Leung and Starmer, 2005). The National Transportation Safety Board (2013) has found that risky driving following alcohol consumption can occur at blood alcohol concentrations (BACs) as low as 10 mg/dL and continually worsen to the point where the risk of crashing when the driver is at a BAC of 80 mg/dL is nearly tripled compared to when they are sober.

Some laboratory studies have examined the acute effects of alcohol on risky behavior in driving simulators (see: Burian et al., 2002, Burian et al., 2003; Cohen et al., 1958; Laude and Fillmore, 2015; Leung and Starmer, 2005). In general, these studies have shown that alcohol increases risky driving. Risk-taking in driving simulator studies is often measured by proxemics, indicated by instances where drivers maneuver close to other vehicles on the road and experience reduced time to avoid potential collisions, such as tailgating. Simulator studies in our lab and in others that measure drivers’ time-to-collision (TTC) have repeatedly found that participants display riskier driving (e.g., lower TTC values) after doses of alcohol at BACs ranging from 50 to 80 mg/dL compared with placebo (Burian et al., 2002, Burian et al., 2003, Cohen et al., 1958, Laude and Fillmore, 2015, Laude and Fillmore, 2016, Leung and Starmer, 2005, Van Dyke and Fillmore, 2017).

These studies also report considerable individual differences in the degree to which risky driving behavior is increased under alcohol. Reasons for such individual differences in risky driving under alcohol is unclear. However, some evidence suggests that drivers’ perceived level of impairment could contribute to increased risk-taking under alcohol. A study by our group found that drivers who underestimated their BAC tended to be the riskiest drivers in the simulator (Laude and Fillmore, 2016). BAC underestimation could indicate a belief that one’s driving ability is not appreciably impaired by alcohol, possibly obviating any perceived need to exert additional caution to the potential impairing effects on their driving.

BAC underestimation might also be a marker of tolerance to the subjective effects of alcohol. Studies show that tolerance can readily develop following periods of frequent or heavy alcohol use even in individuals who report non-dependent, “social” use of alcohol (e.g., Brumback et al., 2007; Fillmore and Vogel-Sprott, 1995; Holdstock et al., 2000; Miller and Fillmore, 2014; Townshend and Duka, 2005). As such, drivers with a recent history of heavier drinking could feel less subjectively intoxicated and as a consequence perceive their BAC to be lower than their actual BAC. Studies have found that those who binge drink perceive less impairment under alcohol (Didier et al., 2023) and display heightened confidence in their driving abilities despite being at-risk for crashes (Love et al., 2023) than those who drink lighter. Drivers’ false belief that they are minimally intoxicated may lead to a lack of compensatory mechanisms being used while driving, thus making the driver’s behavior riskier.

Studies of DUI offenders also support a link between a reduced perception of intoxication and risky driving under alcohol. DUI offenders are known to have heavier drinking histories and be riskier drivers compared with the general population (Brinkmann et al., 2002, Cavaiola et al., 2007, Lapham et al., 1997, Nochajski et al., 1994, Peck et al., 1994). Laboratory studies of DUI offenders show that following a standard dose of alcohol they report less subjective intoxication and a greater perceived ability to drive than nonoffenders (Fillmore and Van Dyke, 2020, Roberts and Fillmore, 2017, Van Dyke and Fillmore, 2014). Taken together, evidence suggests that drivers who appraise themselves to be less intoxicated from alcohol could be more prone to risky driving while intoxicated.

The behavioral disinhibiting effect of alcohol could also contribute to driver risk-taking while intoxicated. Alcohol is well-known for its impairing effect on the individual's ability to inhibit inappropriate actions. Laboratory studies show alcohol can increase impulsive behavior by directly impairing inhibitory control (de Wit et al., 2000, Field et al., 2010, Fillmore and Vogel-Sprott, 2000, Fillmore and Weafer, 2011, Fillmore and Van Dyke, 2020, Laude and Fillmore, 2015, Marczinski and Fillmore, 2003, Marczinski et al., 2005, Mulvihill et al., 1997). This has been observed using stop-signal and go/no-go tasks, which are reaction-time tasks that require quick responses to go-signals but also the inhibition of response when stop-signals are presented. Studies also show considerable individual differences in alcohol-induced impairment of inhibitory control with some individuals displaying little disinhibiting effect and others showing marked impairment (Allen et al., 2021, Gan et al., 2014, Weafer and Fillmore, 2008). Studies by our group show that greater alcohol-induced impairment of inhibitory control can predict greater risk-taking in a driving simulator (Fillmore et al., 2008, Laude and Fillmore, 2015). However, findings are equivocal as the relationship has not been consistently observed in these studies, possibly due to small sample sizes.

Taken together, there is evidence to suggest that a driver’s proclivity to risk-take under alcohol might depend largely on their self-appraisal of intoxication and the degree to which alcohol impairs their inhibitory control. The purpose of this study was to examine simulated driving behavior in a large group of adult drivers to test the effect of an acute dose of alcohol on their risk-taking. The study sought to determine the degree to which individual differences in driver risk-taking under alcohol could be predicted by drivers’ self-appraisal of their alcohol intoxication (i.e., self-estimation of BAC and subjective intoxication) and the degree to which alcohol impaired their inhibitory control. Based on findings to date, it was predicted that drivers who display the greatest risk-taking under alcohol would be those showing greater alcohol-induced impairment of inhibitory control and reduced self-appraisals of intoxication.