A new study by vehicle safety researchers at the University of Iowa Public Policy Center indicates passengers are the most frequent distraction for teen drivers involved in crashes.

The first-of-its-kind study, which reviewed video data of nearly 1,700 crashes involving teen drivers ages 16-19, found that distracted driving contributes to nearly 60 percent of car crashes involving teen drivers.

The study was conducted using in-vehicle event recorders (IVERs), which collect video, audio, and other vehicle data to provide information about what is happening inside a car before a crash occurs. The IVERs are triggered when a driver uses hard braking, fast cornering, or experiences an impact that exceeds a certain G-force.

Through comprehensive video analysis, UI researchers found distraction was a factor in more than half of teen crashes, which is four times the amount of previous estimates based on analysis of police reports.

After analyzing the IVER data, researchers were able to determine that attending to passengers was the most commonly seen driver behavior across all crash types, with a driver either looking at or talking to a passenger at some point in the six seconds before approximately 40 percent of crashes with passengers present.

UI researchers say the number of potential passenger distractions increased as more passengers piled in the car; 54 percent of vehicle-to-vehicle crashes had one passenger on board, and 74 percent of such crashes had two or more passengers. Passengers were also more likely to be moving around inside the vehicle and making loud noises as their numbers increased.

"These are unique data relative to other methods of measuring driver distraction. Understanding what was presented in the moments leading up to a crash will help provide important data to policymakers," says Daniel McGehee, principal investigator on the project and director of the center's Transportation and Vehicle Safety Research Program.

Though young drivers were most often seen attending to passengers in some way when they were in the car, drivers who traveled alone were most often distracted by cell phone use—the second most frequent behavior observed during the six seconds leading up to a crash.

The study found young drivers used cell phones two times more often when they were alone in the car and texting was observed twice as often as talking on the phone.

"Our research found that passengers and cell phone use were common distractions for teenagers in the seconds leading up to a crash," says Cher Carney, senior research associate with the Transportation and Vehicle Safety Research Program. "Limiting teens' exposure to behaviors that have both a high frequency and have been associated with high crash risk in previous research is crucial to reducing teen crashes."

Cell phone use was also associated with longer reaction times and longer "eyes off the road" times than attending to passengers. Additionally, more than 50 percent of drivers using cell phones had no reaction before impact, while nearly 90 percent of drivers distracted by passengers displayed at least some level of reaction before a crash.

The study was funded by the AAA Foundation for Traffic Safety.

Read a link to the full report.