CHICAGO -- Children may be safest in cars when grandma or grandpa is driving instead of mom or dad, according to study results that made even the researchers do a double-take.
"We were surprised to discover that the injury rate was considerably lower in crashes where grandparents were the drivers," said Dr. Fred Henretig, an emergency medicine specialist at Children's Hospital of Philadelphia and the study's lead author.
Previous evidence indicates that car crashes are more common among older drivers, mostly those beyond age 65.
The study looked at injuries rather than who had more crashes and found that children's risk for injury was 50 percent lower when riding with grandparents rather than with parents.
The results are from an analysis of State Farm insurance claims for 2003-07 car crashes in 15 states and from interviews with the drivers.
The data involved nearly 12,000 children up to age 15.
Dr. Henretig, 64, said the study was prompted by his own experiences when his first grandchild was born three years ago.
"I found myself being very nervous on the occasions that we drove our granddaughter around and really wondered if anyone had ever looked at this before," he said.
Reasons for the unexpected findings are uncertain, but the researchers have a theory.
"Perhaps grandparents are made more nervous about the task of driving with the 'precious cargo' of their grandchildren and establish more cautious driving habits" to compensate for any age-related challenges, they wrote.
The study was released online today in the journal Pediatrics.
Joseph Schofer, a Northwestern University professor and transportation expert not involved in the research, noted that the average age of grandparents studied was 58.
"Grandparents today are not that old" and do not fit the image of an impaired older driver, he said. "None of us should represent grandparents as kind of hobbling to the car on a walker."
Grandparents did flub one safety measure.
Nearly all the children were in car seats or seat belts, but grandparents were slightly less likely to follow recommended practices, which include rear-facing backseat car seats for infants and no children in front seats.
But that did not seem to affect injury rates.
Only about 10 percent of children in the study were driven by grandparents, but they suffered proportionately fewer injuries.
Overall, 1.05 percent of children were injured when riding with parents, compared with 0.7 percent of those riding with grandparents -- a 33 percent lower risk.
The difference was even more pronounced -- 50 percent -- when the researchers took into account other things that could influence injury rates, including older-model cars and not using car seats.
Children suffered similar types of injuries, including concussions, other head injuries, and broken bones, regardless of who was driving.
The study does not include data on deaths, but Dr. Henretig said there were very few.
It also lacked information on the types of car trips involved; for example, driving in busy city traffic might increase chances for crashes with injuries.
Mr. Schofer, the Northwestern professor, said other unstudied circumstances could have played a role.
For example, grandparents could be less distracted and less frazzled than busy parents dropping their children off at school while rushing to get to work or to do errands.
Driving trips might be "quality time" for older drivers and their grandchildren, Mr. Schofer said.