PHILADELPHIA --- A study released last month in the journal Pediatrics from the research alliance of the Children's Hospital of Philadelphia (CHOP) and State Farm Insurance Companies sheds light on an often-overlooked group of teen drivers: those without a license.

According to national traffic fatality data, this group is disproportionately involved in fatal crashes. The 2006 National Young Driver Survey (NYDS) of more than 5,500 teens across the country revealed that about 6 percent of students in grades 9 through 11 reported driving unsupervised without a license. However, according to the national fatality data, a full 20 percent of 14- to 18-year-old drivers involved in fatal crashes in 2006 did not have a license. This means unlicensed teens are significantly over-represented in fatal crashes.

"According to our survey, unlicensed teen drivers engage in unsafe driving behaviors more often than their legally driving peers," said Dr. Flaura Koplin Winston, co-scientific director of CHOP's Center for Injury Research and Prevention and a co-author of the study. "Unlicensed teens are more likely to report not wearing a seat belt, driving under the influence of drugs or alcohol, and driving without a purpose, behaviors known to be associated with fatal crashes."

Winston co-wrote the study with Michael Elliott, a biostatistician at the University of Michigan School of Public Health, and Dr. Kenneth Ginsburg of CHOP.

"This issue also impacts those who share the roads with unlicensed drivers," noted Laurette Stiles, vice president of strategic resources at State Farm.

Researchers say knowing which teens are driving without a license makes it possible to develop effective interventions to address unsafe behaviors linked to an elevated risk of injury and death.

"Not all kids who are driving unlicensed are doing so for the same reasons," explained Winston. "Some are simply more likely to take risks with their driving -- such as driving under the influence -- which prevent them from getting or keeping a license. However, there also may be teens who need  to drive to work or school but are unable to obtain or maintain a license for reasons unrelated to driving behavior, such as unpaid fines or registration fees."

Unlicensed teens surveyed in the NYDS were much less likely to have attended a driver's ed class than licensed teens and were about four times more likely to report that "no one" taught them to drive compared to licensed teen drivers.

Further research is needed to better understand and address the obstacles teens face in obtaining a license. The study's authors noted that while a license itself doesn't enhance safety, the licensure process may be protective if it helps teens and their families adhere to graduated driver licensing (GDL) laws and follow a systematic approach to learning to drive. Future research and outreach directed at teens from central city and rural areas may help to reduce the high rate of crash injury and fatality associated with unlicensed teens.

Motor vehicle crashes remain the No. 1 cause of death among teens in the United States. Teen drivers (ages 16 to 19) die at four times the rate of adult drivers (ages 25 to 69). To reduce injury and death from young driver-related crashes through scientific research and outreach, the Children's Hospital of Philadelphia and State Farm Insurance Companies have formed an alliance called the Young Driver Research Initiative (YDRI). This academic-industry alliance also created Partners for Child Passenger Safety, the world's largest study of children in crashes.