Circadian sleep propensity, alcohol consumption and traf fi c crash risk

Objectives: The study was aimed at estimating the risk of traffic crashes associated with alcohol consumption, sleep propensity, and their interaction in a speci fi c regional context. Methods: Blood alcohol concentration (BAC) data were collected from drivers involved in traf fi c crashes during one year in an Italian region and in a control group of drivers over the same road network. Circadian sleep propensity was estimated from a previous study as function of time of day. Crash risk was analyzed by logistic regression as function of BAC and circadian sleep propensity. Results: BAC values greater than zero were found in 72.0% of the drivers involved in crashes and in 40.4% of the controls. Illegal BAC values (above the 0.05 g/dL threshold) were found in 23.6% of the drivers involved in crashes, and in 10.4% of the controls. The relative risk showed a signi fi cant increase with both BAC and circadian sleep propensity and their interaction was signi fi cant. Conclusions: Due to the signi fi cant interaction, even low BAC levels strongly increased accident risk when associated with high sleep propensity. The present fi ndings motivate educational campaign and reconsideration of legal limits for alcohol concentration to definitely discourage driving in risky condition.