Spring 2016

HSRC study examines effect of school start times on teen crashes

Most parents will tell you – waking up early is not easy for the typical 16- or 17-year-old. School administrators recognize that, too. Since research has suggested that lack of sleep impairs functioning, some school districts have pushed start times from 7:15 a.m. or earlier to a time more aligned with teen’s biologically-controlled sleep cycle. This has led to improved academic performance and behavior.

Given that drowsy driving is a problem for drivers of all ages, including teens, HSRC researchers wondered: could this change in school start times also lead to fewer teen driver crashes? While this issue had previously been investigated, those initial studies used weak research methods. HSRC sought to conduct a more scientifically rigorous examination.

HSRC researchers teamed with Professor Richard Smith of the UNC Department of Statistics and Operations Research to examine crash data before and after high school start times were changed in Forsyth County, North Carolina. Investigating these data required much more than simple comparisons of the number of crashes before and after the time change, however.

“Simply comparing communities with different start times, as some previous studies have done, cannot answer the question of whether the school start time is responsible for a difference in crash rates,” said Foss. “That approach cannot separate the effect of a school start time from effects of different driver training, licensing regulations, driving conditions, roadways, economic conditions or other factors that influence crash rates.”

To improve their ability to clearly see the effects of school start time alone, the research team conducted sophisticated time series analyses, examining monthly crash rate data among 16- and 17-year old licensed drivers in several large North Carolina counties (comparing those that did and did not change their school start times). Careful controls for driving “exposure” were made, adjusting for the exact number of school days in each month as well as county-specific changes in population among the 16- and 17-year-old age group.

Compared to similar counties with no change in school start time:

So, does changing the opening bell from 7:30 to 8:45 a.m. reduce crashes? Probably, but the pattern of results is complex. Findings did suggest the change in crash rates had little to do with changes in drowsy driving. Shifting the school start time alters the peak crash times and appears to reduce the amount of after-school driving by compressing the after-school driving period. Foss says that additional studies of crashes in other jurisdictions that have altered their start times, and where the teenage driving population is sufficiently large to provide the needed statistical power to detect an effect, would be highly useful in bringing clarity to this issue.

For more information, please view a copy of the study, available online.

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