although the increased risk associated with driving under the influence of alcohol or benzodiazepines on their own has been recognized, several variables make their combined effects difficult to study. as a result, the small body of research on the subject is contradictory. the current study aimed to further explore the effects of the combination of alcohol and benzodiazepines on driving. data from the years 1993 - 2006 were taken from the american fatality analysis reporting system and examined using a case control design. all subjects were drivers, aged 20 years and older, had been tested for alcohol and drugs, and, if positive for benzodiazepines, were only positive for a single half-life class of benzodiazepine. cases had at least one unsafe driver action (e.g., weaving) recorded in relation to the crash. controls had no such record. logistic regression was performed to determine the odds ofperforming an unsafe driver action (uda) for drivers positive for benzodiazepines (stratified by short, intermediate and long half-life) with bacs ranging from 0.00 to 0.10 mg/100 ml. when compared to an alcohol- and benzodiazepine-free referent group, the alcohol plus benzodiazepine groups showed significantly higher odds of committing an uda at nearly every bac / half-life combination. when using the alcohol only and benzodiazepine only groups as referents, additive, possibly synergistic effects were observed for long benzodiazepines in combination with alcohol at bacs of 0.02 and 0.04 mg/100 ml. this study demonstrates the detrimental effects that the combination of alcohol and benzodiazepines can have on driving, and suggests that further research is necessary.