Adolescent crash rates and school start times in two central Virginia counties, 2009-2011: a follow-up study to a southeastern Virginia study, 2007-2008.

BACKGROUND AND OBJECTIVE Early high school start times (EHSST) may lead to sleep loss in adolescents ("teens"), thus resulting in higher crash rates. (Vorona et al., 2011). In this study, we examined two other adjacent Virginia counties for the two years subsequent to the above-mentioned study. We again hypothesized that teens from jurisdictions with EHSST (versus later) experience higher crash rates. METHODS Virginia Department of Motor Vehicles supplied de-identified aggregate data on weekday crashes and time-of-day for 16-18 year old (teen) and adult drivers for school years 2009-2010 and 2010-2011 in Henrico and Chesterfield Counties. Teen crash rates for counties with early versus later school start-times were compared using two-sample Z-tests and these compared to adult crash rates using pair-wise tests. RESULTS Henrico teens manifested a statistically higher crash rate of 48.8/1000 licensed drivers versus Chesterfield's 37.9/1000 (p = 0.04) for 2009-2010. For 2010-2011, HC 16-17 year old teens demonstrated a statistically significant higher crash rate (53.2/1000 versus 42.0/1000), while for 16-18 teens a similar trend was found, albeit nonsignificant (p = 0.09). Crash peaks occurred 1 hour earlier in the morning and 2 hours earlier in the afternoon in Chesterfield, consistent with commute times. Post hoc analyses found significantly more run-off road crashes to the right (potentially sleep-related) in Chesterfield teens. Adult crash rates and traffic congestion did not differ between counties. CONCLUSIONS Higher teen crash rates occurred in jurisdictions with EHSST, as in our prior study. This study contributes to and extends existing data on preventable teen crashes and high school start times.