Adolescent sleep, school start times, and teen motor vehicle crashes.

STUDY OBJECTIVES To assess the effects of delayed high-school start times on sleep and motor vehicle crashes. METHODS The sleep habits and motor vehicle crash rates of adolescents from a single, large, county-wide, school district were assessed by questionnaire before and after a 1-hour delay in school start times. RESULTS Average hours of nightly sleep increased and catch-up sleep on weekends decreased. Average crash rates for teen drivers in the study county in the 2 years after the change in school start time dropped 16.5%, compared with the 2 years prior to the change, whereas teen crash rates for the rest of the state increased 7.8% over the same time period. CONCLUSIONS Later school start times may both increase the sleep of adolescents and decrease their risk of motor vehicle crashes.