By Nolan Feeney
March 25, 2015

Americans already know that teenagers do some very alarming things while driving—like changing their clothes and doing homework—but a new study finds that distracted driving is a bigger problem than widely thought, responsible for four times as many car crashes as previous police report-based estimates suggested.

Looking at in-vehicle video footage of roughly 1,700 teen drivers, researchers for AAA Foundation for Traffic Safety found that in the six seconds leading up to the crash, distraction played a role 58 percent of the time. Previous estimates from the National Highway Traffic Safety Administration stated that distraction played a role in only 14 percent of crashes involving teen drivers.

The leading distractions were interactions with other passengers (occurring before 15 percent of crashes), mobile phone use (12 percent of crashes) and looking at something inside the car (10 percent of crashes). Of those final six seconds before a crash, mobile phones took teenagers’ eyes off the road for an average of 4.1 seconds. Additionally, teenagers using their phones before a crash did not brake or steer before the collision, suggesting that cellphones have a serious effect on teen drivers’ reaction times compared to other distractions.

Read next: Here Are All the Very Alarming Things Teenagers Apparently Do While Driving

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Write to Nolan Feeney at nolan.feeney@time.com.

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