The relationship between blood alcohol concentration (BAC), age, and crash risk

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Abstract

Problem

The role of age (youth and driving inexperience) and alcohol as major risk factors in traffic crash causation has been firmly established by numerous studies over the past 50 years. Less well established is how the two variables interrelate to influence crash risk. Some investigations have hypothesized an interactive or synergistic effect in which young drivers with less experience and a greater tendency to take risks are more adversely affected at lower blood alcohol concentrations (BACs) than are older drivers. The evidence for this hypothesis is mixed. Resolution of this issue has important implication for developing countermeasures directed at the young driver crash problem.

Method

Case control data previously collected in Long Beach and Fort Lauderdale were reanalyzed using a more sensitive method for detecting interaction effects than used in the original analysis. A conditional logistic regression analyses found a highly significant age × BAC interaction (P < .0001) involving differences between drivers under 21 and those 21 and older.

Discussion

The results clearly indicate that positive BACs in drivers under 21 are associated with higher relative crash risks than would be predicted from the additive effect of BAC and age. It is likely that two mechanisms are operating to cause the interaction. First, it seems likely that the crash avoidance skill of young novice drivers would be more adversely affected by alcohol due to their driving inexperience, immaturity, and less experience with alcohol. Second, drivers under 21 who choose to drink and to drive after drinking probably have pre-existing characteristics that predisposed them to risk taking and crash involvement apart from any increased vulnerability to alcohol impairment.

Impact on Industry

The results support increased enforcement of zero-tolerance BAC laws for minors.

Section snippets

Problem

Both age (youth) and alcohol-impairment are strong independent correlates of increased crash risk. This fact has been demonstrated by innumerable studies of traffic crash causation and driver performance over the past 50 years.

In a study of California drivers, Janke, Masten, McKenzie, Gebers, and Kelsey (2003) reported that crash rates were highest for drivers under 21 years of age and declined to age 50–54 for crashes per mile driven and to age 65–69 for crashes per licensed drivers. Drivers

Data

All data used in this study were collected by Blomberg et al. (2005) in connection with a case control study of the relationship between blood alcohol concentration (BAC) and crash risk. Prior to initiating the present analysis, the data were re-edited for accuracy and internal consistency. Five errors or highly questionable values were found, four of which affected BAC scores and one that affected a passive alcohol sensor (PAS) value. Two of the BAC errors were due to decimal misplacement on

Results

The number of drivers in each of the four age groups used in the logistic regressions is tabulated by outcome, BAC, and relative risk in Table 1. The same tabulation for gender is shown in Table 2. The tabulations illustrate simple bivariate relationships that have not been adjusted for other covariates. These relative risks represent the simple odds of crash involvement of each positive BAC group (number with crashes/number in control) compared to odds of crash involvement of 0-BAC drivers.

Discussion

Taken together, the results provide strong support for the hypothesis that the association between BAC and crash risk is higher in young drivers than older drivers. The results also indicate that the interaction is largely confined to a single age group, drivers under 21. None of the interaction contrasts involving the 21 and over sub-groups approached significance.

There are a number of reasons for believing that young and inexperienced drivers would be more vulnerable to the effects of

Acknowledgement

We thank the National Institute on Alcohol Abuse and Alcoholism, which provided support for this work (grant number R21AA015093). The authors also wish to thank Ellie Enriquez Peck for her assistance in typing drafts of the manuscript.

Raymond C. Peck is President of R.C. Peck & Associates, Folsom, CA and Senior Project Analyst at Pacific Institute for Research and Evaluation, Calverton, MD. He holds a M.A. in Experimental Psychology from California State University.

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  • Cited by (0)

    Raymond C. Peck is President of R.C. Peck & Associates, Folsom, CA and Senior Project Analyst at Pacific Institute for Research and Evaluation, Calverton, MD. He holds a M.A. in Experimental Psychology from California State University.

    Michael Gebers is a Research Program Specialist at the California Department of Motors, Sacramento and a Statistical Consultant with R.C. Peck & Associates. He holds an M.A. in Experimental Psychology from California State University.

    Robert Voas is a Senior Research Scientist with Pacific Institute for Research and Evaluation; Vice President and Director of Alcohol Programs at the National Public Services Research Institute, Landover, MD; and Consulting Senior Scientist with the Vermont Alcohol Research Center, Burlington, VT. He holds a Ph.D, M.A., and B.A. from UCLA and a Ph.B from the University of Chicago.

    Eduardo O. Romano is Associate Research Scientist at the Pacific Institute for Research and Evaluation. He holds a Ph.D. and M.S. from Virginia Polytechnic Institute and State University and an Ing. Agr. from University of Buenos Aires.

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