When the school bell rings an hour later each morning, teens may be significantly less likely to get into car accidents.

That’s the take home message from U.S. researchers who compared sleep times and auto accident rates among high school students in Kansas, before and after school start times were delayed by one hour. Researchers found a 16.5 percent drop in auto accident rates for teen drivers when local high schools moved the start of classes from 7:30 a.m. to 8:30 a.m. More sleep, more alert driving, the researchers said.

Fatigued drivers cause about 100,000 accidents a year and over half of those drivers are 16 to 25 years old, according to the National Sleep Foundation. One 2006 survey by the foundation revealed that 28 percent of high school students fall asleep at school and 51 percent have driven while drowsy. Another recent study showed that sleep deprivation also leads to safety problems for college students. A survey of 262 students at the University of North Texas found that 17 percent of them reported falling asleep while driving.

Studies show moving the start of school can help teenagers catch up on much needed sleep. One school district in Kansas had middle school and high school begin classes one hour later. Researchers from the University of Kentucky surveyed thousands of middle school and high school students both before, and after, a one-hour shift in start times. Middle school began at 9 a.m. instead of 8 a.m., and high school started at 8:30 a.m. rather than 7:30 a.m.

As a result to that, teen car crash rates declined 16.5% in the two years after the change. Whereas, elsewhere in the state, adolescent crash rates increased by nearly 8%. Results showed that the percentage of kids reporting 8 hours of sleep on weeknights rose from 36 percent to 50 percent.

Teens sleep less because, with age, they are starting to stay awake until very late, watching movies or playing on their PCs. So schools should be prepared to handle the increasing pressure, by modifying their start times.