Grandparents might be more cautious, less harried when transporting the "precious cargo" of their grandchildren, according to a study released Monday in Pediatrics. The study found children were half as likely to be injured in car wrecks when their grandparents were driving than when their parents were driving.

The results actually surprised the Philadelphia-based researchers, who examined 1998-2007 accident claims data from State Farm auto insurance and compared injury rates among children by who was driving them around. A detailed story on the study results can be found on Startribune.com. The lower rate of injuries came despite the fact that grandparents were worse at using and installing car seats properly and were more likely to drive older cars or vehicles such as pickups with poorer safety records, the study found.

Dr. Fred Henretig, an emergency medicine specialist at Children's Hospital of Philadelphia, conceived the study idea when driving around his own grandchildren, according to an AP story.

There are several possible explanations, including that grandparents simply have more time to be careful with their driving. Parents might be rushing between work and dinner and youth activities and spending less time on safe driving. The average age of the grandparents in the study was only 58. The study didn't examine the accident data by types of car trips -- family vacations versus trips to the corner store, etc.

It did compare the speed limits of the roads on which accidents happened, though. Grandparents transporting their grandchildren were somewhat less likely to be involved in accidents on roads with speed limits of 35 MPH or higher.