Sleep related vehicle accidents on Italian highways.

Sleepiness has been identified as a significant risk factor for vehicle accidents, and specific surveys are needed for Italy. The aim of this study was to assess incidence and characteristics of sleep-related vehicle-crashes on Italian highways. The database of the Italian National Institute of Statistics (1993-1997) was the source for the survey (50859 accidents with 1632 (3.2%) ascribed to sleep by the police). The distribution of accidents was evaluated by means of the analysis of variance considering the year, the day of the week, the age and the time of day and their interactions as main factors. The relative risk of sleep-related accidents was also evaluated with reference to the relative traffic density as estimated by the Italian Highways Society. The counts of sleep-related accidents, and even more the relative risk, revealed the presence of peaks and troughs in zones at a higher level of sleepiness and alertness respectively. Death of the driver occurred in 11.4% of sleep related accidents versus 5.6% in general accidents. The great majority of sleep-related accidents occurred to drivers under 35 (61.4%) mainly during the night with an increasing trend in the yearly number of sleep-related accidents, especially on weekends. Therefore sleepiness appears a remarkable risk factor and, in our opinion, its incidence as sole or contributory cause of accidents on Italian highways is still underestimated.