THURSDAY, Oct. 20 (HealthDay News) -- Crash experts studying why newly licensed teenagers have many more accidents than adults have zeroed in on the elevated gravitational forces, or "g-forces," caused by braking late, swerving abruptly and other common new-driver mistakes.

These judgment-related maneuvers make losing vehicle control more likely and leave less time to react to hazards, said researchers with the U.S. National Institutes of Health. They also limit the ability of nearby drivers to take corrective measures.

To explore the young-driver dynamic, the NIH team studied 42 newly licensed teens -- 22 females and 20 males -- who attended high school or home school in Virginia. For comparative purposes, the researchers also assessed the driving habits of 55 parents operating the same vehicles. All were tracked for a total of 18 months between 2006 and 2008.

"This is the first naturalistic or objective assessment of teenage risky driving," explained Bruce G. Simons-Morton of the division of epidemiology, statistics and prevention research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the NIH.

"Sadly, it points out the teenage driving dilemma, which is that newly licensed drivers of all ages, but particularly teenagers, are a high risk for accidents early on," he said.

Simons-Morton, who spoke Thursday morning at an NIH teleconference, is the lead author of the study published online Oct. 20 in the American Journal of Public Health.

Novice teen drivers are almost four times as likely to end up in a car accident or close-call as adult drivers, the study found. And risky driving is five times more prevalent among new teen drivers, as compared with older, experienced drivers. Even a year or more out, as young drivers gain experience, their risky driving behavior persists, with accident rates remaining several times that of adults, the study found.

For the study, within three weeks of the teens acquiring a provisional license, their cars were outfitted with surveillance systems to collect information on acceleration and mileage. Internal and external video were also installed to monitor the driver's face, dashboard and hand action, as well as the unfolding rear and front roadway.

Over the study period, the teens experienced higher rates of crashes or near-crashes compared with parents -- 37 crashes and 242 near-crashes versus just 2 crashes and 32 close-calls among the adults.

The spread was driven by the much higher g-forces at play whenever teens took the wheel. For example, teens engaged in sharp turning 25 to 30 times more often than their parents, Simons-Morton said.

The sort of risky driving behavior, including excessively fast acceleration, that prompts g-force spikes did not subside among teen drivers, despite a significant drop in accident risk. Indeed, while lower at the study's conclusion than at its outset, accident risk remained markedly above that of the adult drivers, who almost never experienced a g-force event. The parents' rate of incidents remained steady throughout the study period.

The NIH team concluded that their work generated "no support for the contention that risky driving declines with experience and that adolescents learn to reduce risky driving behavior."

Simons-Morton said it remains unclear why teens maintain dangerous driving habits, hypothesizing that as they get better at handling risky g-force maneuvering, young drivers keep it up, either because they think it's "fun" or are "simply clueless" about related safety concerns.

Ultimately, it can take years before accident risk of teens finally matches that of experienced adult drivers, the study said.

As a result, parents should be pro-active about limiting the number of passengers their children drive with, and curtailing late-night driving and the use of high-speed roads and electronic devices, Simons-Morton said.

Car accidents are the number one cause of death and disability among teens, with crash risk at its peak the very moment young drivers obtain their licenses, the researchers said.

More information

For more on teens and driving, visit the U.S. Centers for Disease Control and Prevention.