Researchers recruited 52 North Carolina high-school age drivers to have in-vehicle cameras mounted in their cars and trucks to observe distracted driving behaviors and distracted conditions when teen drivers were behind the wheel.
Young drivers were recorded in a variety of real-world driving situations over six months - with parents in the car, with other teens in the car and alone.
The study showed that young drivers were less likely to use cell phones and other technology (including in-vehicle systems, like the radio and temperature control) when there were passengers in the car with them.
But having multiple passengers in the car more often led to more serious incidents.
Teen drivers were six times more likely to have a serious incident when there was loud conversation in the vehicle - to the point of needing to make an evasive manoeuvre to avoid a crash - and three times more likely to have a serious incident when there was horseplay in the vehicle.
Another important finding is that actions the driver alone controls - reaching, texting, using a phone and eating - seem less likely to lead to a serious incident than things they can't control, like how others in the car behave.
"This is why the limit of one teen passenger is important when teens are just learning to drive," said Foss, who is also director of the Center for the Study of Young Drivers.
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