Forget cellphones; rambunctious friends may be the riskiest driver distraction for teens, according to a new study. Researchers installed video and G-force recorders in the vehicles of 52 newly licensed high school students for 6 months. They found that certain distractions, such as fiddling with the car’s controls and eating, were not strongly related to serious incidents, which included collisions and evasive maneuvers. However, when passengers in the car were engaged in loud conversation, teen drivers were six times more likely to have a serious incident. What’s more, horseplay increased risk by a factor of three whereas cellphone use only doubled it, the team reported online this week in the Journal of Adolescent Health. Forty-three states restrict newly licensed drivers from having more than one other teen in the car, and the study authors say their data suggest that's good policy.