Triple-A is warning that Memorial Day weekend marks the start of a dangerous time of year for young drivers. The organization says more than 30% of deaths involving teen drivers occur between Memorial and Labor Day, a period unofficially known as the "100 Deadliest Days." Traffic accidents are the leading cause of death for U.S. teens ages 16 to 19. Triple-A recommends teens go through about 50 hours of supervised driving practice and enroll in an in-person driving course.