The two age groups most at risk for getting into car accidents are teenagers and the elderly. The reasons for the high accident rate in each group are obviously different. Elderly people’s faculties tend not to be as sharp as they once were. Reaction time slows. Eyesight and hearing decline. The causes of teen car accidents are completely different. Besides lack of experience, there is risk-taking behavior and poor judgment. But one factor in the high rate of teen car accidents is getting more attention in recent years: sleepiness. It is well known that early high school start times make for sleepier teenagers. Now there is a growing body of scientific literature that is suggesting a link between school start time and car accidents.
What Does School Start Time Have to Do With Teen Car Accidents?
In 1998, University of Kentucky researchers Fred Danner and Barbara Phillips got word that a single county in their state planned to increase high school start time. In 1998, schools in the county started at 7:30 am. In 1999 start time was moved to 8:30 am. The remainder of the state kept the same start time. Danner and Phillips seized on this opportunity to test whether the change in start time would have any effect effect on the rate of teen car accidents.
Danner and Phillips found that high schoolers in all four years got substantially more sleep in 1999 than in 1998. The number of students getting the recommended amount of sleep, 9+ hours, increased from 6.3% to 10.8%. The number of students getting at least 8 hours increased from about one-third to over 50%.
But the most interesting finding was the drop in the rate in teen car accidents.
Despite rapid population growth, with many more cars on the road, the rate of crashes in the study county dropped after the change in school start time. The average crash rates in the 2 years after the change in school start times dropped 16.5% in the study county. At the same time, the car accident rate increased 7.8% in the rest of the state.
Need a SLEEP COACH?
Danner and Phillips were careful not to conclude that the school start time directly caused fewer accidents. The study hampered by the unforeseen circumstance that the student ID numbering system changed between 1998 and 1999. As a result, the investigators could not go back and find out if particular teens involved in accidents were sleeping more or less.
The Virginia High School Start Time Study
One study alone cannot answer a question. This is especially so when the study only shows a correlation (as opposed to a causal relationship) between teen sleep and car accidents. Any scientific question is best answered by several studies looking at the same problem. In 2011, a group of researchers at Eastern Virginia Medical School published a study similar to the 2008 Danner and Phillips study.
The Virginia investigators compared teen driver accident rates in two neighboring counties with different high school start times. The Virginia Beach district started high school 75-80 minutes earlier than the neighboring Chesapeake district. The investigators guessed that the rate of teen car accidents would be higher in Virginia Beach than in Chesapeake.
This is indeed what they found.
For Virginia Beach and Chesapeake, teen drivers’ crash rates in 2008 were 65.8/1000 and 46.6/1000, respectively. In 2007 were 71.2/1000 and 55.6/1000. Teen drivers accident peaks in the morning occurred one hour earlier in Virginia Beach than in Chesapeake, consistent with school commute time. Congestion data for the two towns did not explain the different accident rates.
The Australian Teen Car Accidents Study
This study, published in 2013, was the first study of teen car accidents that was prospective as opposed to retrospective. That is, a large group of young people (over 19,000!) was signed up to participate. They were then followed over a number of years, while carefully documenting hours of sleep and other important contributing factors.
Here’s what they found: On average, teens who reported sleeping 6 or fewer hours per night had an increased risk for accidents compared with those who slept more than 6 hours. If the teen slept less on weekends, they were more likely to be involved in “run-off-road” accidents. Peak hours for these accidents occurred between 8 pm and 6 am.
Whereas the study did not address school start times as such, it offers some very strong data to the body of literature. First, it was a very large study. It also controlled for various factors that could skew the results of a smaller studies. As the evidence grows stronger that sleepiness leads to car crashes, the case for later school start times becomes stronger as well.
Back to Virginia
Finally we look at a second study published in 2014 by the Eastern Virginia Medical School group. This time, the investigators compared data for teen car accidents in two neighboring counties in central Virginia. Henrico County schools began at 8:45 am and Chesterfield County schools began at 7:20 am. This time, investigators not only compared the rate of teen car accidents in each county, they also compared the rates of adult accidents as a comparison group.
For 2009-2010, Chesterfield teens had a higher accident rate than the later starting Henrico teens. There was no such difference in adult crash rates for either year in Henrico County and Chesterfield County, making it less likely that a systemic (not teen-specific) difference between the two counties was to blame for the difference.
Investigators also found two peak hours for teen car accidents, one in the morning when teens drive to school, and another in the afternoon when sleep deprivation begins to kick in.
Putting It All Together
One study never answers an important scientific question. The more studies that look at a question, the more likely we are to come up with an answer that approaches the truth. As the body of evidence grows, we are beginning to see a picture emerging that describes the dangers of early school start time for high schoolers. It seems that teens who must get up earlier than they should are more dangerous on the road.
There is an easy fix for this one. Start school later. There are a number of objections to this concept that deserve attention. Indeed attention has been paid to these objections. We will address them in future posts.