According to the author, "The series analyzed fatal motor vehicle crashes in the United States in which at least one driver was between the ages of 14 and 19. Among the major findings: Speeding contributed to more than half of the wrecks. More than two-thirds of people killed in cars driven by teens were not wearing seat belts. More than half of the wrecks were single-vehicle crashes. More than three-quarters of the crashes involved sober drivers."