Drunk driving has a speeding problem.

Abstract

Objectives: Alcohol and excessive speeding are both linked to elevated crash risk. Alcohol-related and speeding-related crashes are recorded and treated as distinct, with separate etiologies. Yet, speeding and alcohol use are interrelated. We speculate that speeding might account for some of the crash risk associated with drunk driving.

Methods: Data from the Crash Investigation Sampling System were analyzed. Vehicle speeds, measured moments before crashes, were estimated from driver blood alcohol concentrations (BACs) for different levels of injury severity. We first applied a previously published formula to estimate the relative crash risk associated with speeds that occur at different BACs. Then, from the literature we obtained relative crash risk odds ratios associated with different BACs. Finally, for BACs of 0.08 g/dl and 0.16 g/dl, separately for serious injury and fatality crashes, we created ratios to estimate what portion of the alcohol-crash risk might be attributed to higher travel speeds.

Results: A statistically significant BAC × Injury Severity interaction indicated that crash drivers with higher BACs drove faster than their sober counterparts, and that this was exacerbated for more serious injuries. Among drivers with fatal injuries, those with BACs of 0.16 g/dl were traveling over 10 mph faster than their sober counterparts. Finally, using this information, for drivers at different BACs, we compared the crash risk attributable to speed with the crash risk as a function of alcohol levels. Accordingly, we estimate that at 0.08 g/dl, higher speeds accounted for nearly 50% of the fatality crash risk attributed to alcohol, and 25% of the fatality crash risk at 0.16 g/dl. For serious injuries, estimates were 39% and 16%, respectively.

Conclusions: The literature on alcohol-related crashes widely attributes the increased crash risk to impaired driving skills, such as attention, coordination and reaction time. Our analysis suggests that speeding alone might account for some of this elevated risk. This has implications for understanding the etiology of alcohol-related crashes. We also suggest that speed control may be a viable means of reducing the harm from alcohol-related crashes.