School start time change and motor vehicle crashes in adolescent drivers.

STUDY OBJECTIVES

The aim of this study was to examine the association between a 50-minute delay (7:20 am to 8:10 am) in high school start times in Fairfax County (FC) Virginia and changes in rates of adolescent motor vehicle crashes. Crash rates in FC were also compared to those in the rest of the state during the same time period.

METHODS

Virginia Department of Motor Vehicles crash data in drivers age 16 to 18 years old between September and June of each year in FC versus the rest of the state were compared in the combined 2-year periods preceding (2013-2014 and 2014-2015; T1) and following (2015-2016 and 2016-2017; T2) school start time change in the fall of 2015.

RESULTS

The crash rate per 1000 in 16- to 18-year-old licensed drivers in FC during T1 was significantly higher compared to T2, 31.63 versus 29.59 accidents per 1,000 (95% confidence interval, 1.0-1.14, odds ratio 1.07, P = .03). In contrast, adolescent crash rates in the rest of Virginia were not statistically significantly different at T1 versus T2. With regard to subtypes of crashes, there was a trend toward significance in distraction-related crashes per 1,000 in FC at T1 compared to T2 at 7.01 versus 6.13 (95% confidence interval, 0.99-1.31, odds ratio 1.14, P = .05), but were not significantly different in the remainder of the state.

CONCLUSIONS

The results of this study suggest that school start time delay is associated with decreased adolescent motor vehicle crash risk, with significant implications for public health and safety.