634 Impact of Changing School Start Times on Drowsy Driving and Teen Motor Vehicle Crashes: A Longitudinal Examination

Abstract

Abstract Introduction Early high school start times are associated with insufficient adolescent sleep, which in turn is associated with motor vehicle crashes [MVC]. This analysis examined the impact of a 70-minute delay in high school start times on student-reported drowsy driving and department of transportation MVC rates before and for 2 years after start time changes. Methods Self-reported sleep duration and drowsy driving data were drawn from a longitudinal study of changing high school start times (n=2099–4092/year) in the Cherry Creek School District (Arapahoe County [AC]). The Colorado Department of Transportation provided frequency/timing of weekday MVC data for teen (16–18 years) and adult drivers in AC and four neighboring counties in metro Denver (Other Counties [OC]). MVC rates per 1000 licensed drivers were calculated. Outcomes are reported for three school years: 2016–17 (pre-change), 2017–18 (post change), and 2018–19 (follow-up). Chi-square analyses examined drowsy driving frequency (at least once/week vs. less than once/week) by sufficient weeknight sleep duration (<8 hours vs. 8+ hours). Two-proportion z-tests compared MVC rates by county, as well as teens vs. adults. Results Compared to pre-change (29.3%), fewer students reported drowsy driving at post-change (20.3%) and follow-up (23.7%). Students who reported insufficient sleep also reported more frequent drowsy driving across all years (p’s<0.001 to 0.037). AC’s teen crash rate decreased from 78.9/1000 to 76.6/1000 post-change, with a further reduction to 68.7/1000 at follow-up. Pre-change crash rates did not differ between counties (p=0.444); however, they were significantly lower in AC vs. OC at both post-change (p=0.048) and follow-up (p=0.046). Adult crash rates remained consistent over three years in both counties. Morning crash rates per hour did not differ pre-change; at both post-change and follow-up OC’s morning crash rates peaked one hour earlier than AC’s (7:00-7:59am vs. 8:00-8:59am). Conclusion This study extends previous reports by finding that later school start times are associated with decreased drowsy driving and fewer teen motor vehicle crash rates for up to 2 years post-change. Early school start times is an important public policy that benefits adolescent sleep, health, and well-being through decreased drowsy driving and motor vehicle crashes. Support (if any) Robert Wood Johnson Foundation’s Evidence for Action Program