MONDAY, Sept. 28 (HealthDay News) -- Your parenting style can make a huge difference in your teen's safety once he or she gets behind the wheel of a car.

Parents who set firm rules, but do so in a helpful, supportive way, can reduce the likelihood of their teen getting into an auto accident by half and decrease rates of drinking and driving, two new studies find. Positive rule-setting can also increase the odds a teen will wear a seatbelt and lessen the likelihood of talking or texting on a cell phone while driving.

"Parent involvement really matters. Active parenting can save teenagers' lives," said Dr. Kenneth Ginsburg, an adolescent medicine specialist at the Center for Injury Research and Prevention at the Children's Hospital of Philadelphia. "Parents who give rules, set boundaries and monitor those boundaries with warmth and support can have a really dramatic effect on teen driving safety."

Ginsburg is the lead author of two studies published online in Pediatrics on Sept. 28. Both studies were sponsored by State Farm Insurance.

The first study looked at the association between parenting styles and teen driving behaviors and attitudes, while the second assessed teen behavior based on their access to a vehicle.

The first study included a nationally representative sample of 5,665 teens in 9th through 11th grades. Parenting style was reported by the teens and fell into one of four categories: authoritative (high support along with rules and monitoring); authoritarian (low support with rules and monitoring), permissive (high support with low rules and monitoring), and uninvolved (low support and low rules).

Teens who had authoritative or authoritarian parents wore seatbelts twice as often as teens with uninvolved parents. Teens with parents in these groups were also half as likely to speed as those with uninvolved parents. Teens with authoritative parents -- high support and rules -- were half as likely to get into a car accident, 71 percent less likely to drink and drive, and 29 percent less likely to talk or text on their cell phones while driving compared to teens with uninvolved parents.

The second study included 2,167 teens and found that 70 percent had "primary access" to a vehicle. That didn't necessarily mean that the teens had their own cars, Ginsburg said, but it could mean they had easy access to the keys and didn't need to ask permission to take a family car.

After controlling the data to account for the extra hours these teens likely spent behind the wheel, the researchers found that teens with easy access to a vehicle were more than twice as likely to crash, about 25 percent more likely to use a cell phone while driving and about 25 percent more likely to speed than teens who had to ask permission to use a car.

Why the difference? Ginsburg said he suspects it's because teens with easy access to a car don't necessarily feel as accountable. They don't have anyone asking where they're going or whom they'll be with. "They miss out on that conversation and appropriate monitoring," he said.

Parents should control the keys to the car for at least the first six to 12 months of driving, he added.

Ginsburg said there are clear rules that must always be followed, and rules that will change as your teen gains experience and demonstrates responsibility.

Clear rules include:

• Always wear your seatbelt.
• Never speed.
• Never drink and drive.
• Never drive fatigued.
• Never use your cell phone or text while driving.

Rules that can change as your child gains experience and skill include having passengers, driving at night, increased access to the car and driving in bad weather. Ginsburg said it's important to make sure there's a reward for your teen for good driving behavior. "There has to be something in it for them," he said.

"Teens do need parents to set rules, and there need to be consequences when the rules aren't followed," said Dr. Barbara Gaines, director of the trauma and injury prevention program at Children's Hospital of Pittsburgh.

"Parents need to know that the moment a child gets a driver's license is the riskiest time in their lives. Don't treat this time as a fait accompli. Getting the license is a goal, and the first step in a process," she said.

Most parents worry more about sex, drugs and drinking than they do about driving, but car crashes are the biggest threat to teen safety, Ginsburg added. "The great news is that parents really matter. And, when you stay involved and do so in a way that promotes safety, not control, driving becomes the greatest opportunity to promote their children's safety."

More information

To learn more about how to set rules to help your teen driver, visit the National Safety Council.

SOURCES: Kenneth Ginsburg, M.D., MS.Ed., adolescent medicine specialist, Center for Injury Research and Prevention, The Children's Hospital of Philadelphia; Barbara Gaines, M.D., director, trauma and injury prevention program, Children's Hospital of Pittsburgh; Sept. 28, 2009, Pediatrics, online

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