Video

Memo to parents: Distracted driving by teenagers is riskier than previously thought, particularly when it comes to multitasking with a cellphone.

This is one finding of research being published on Wednesday that provides sobering video evidence of the extent and nature of the problem.

The study entailed putting video cameras in the cars of drivers ages 16 to 19, allowing researchers to watch the excruciating moments before nearly 1,700 crashes. Time and time again, teenagers in the videos — which will be made available to the public — lose themselves in their devices and then are jarred back to reality when they slam into another car or careen off the road.

The study, published by the AAA Foundation for Traffic Safety, found that distraction was the cause of roughly 60 percent of moderate and severe crashes. The study says this is four times as many as some previous government estimates.

Cellphones were involved in 12 percent of those crashes, making them the second-highest risk factor. Only teenage drivers’ interaction with other passengers — which caused 15 percent of the wrecks — was a factor in more crashes. In the case of phones, drivers manipulating the device had their eyes off the road for an average of 4.1 seconds in the six seconds before a crash, making them effectively blind to roadway conditions.

Half the time in rear-end crashes, teenagers using cellphones failed to react at all in the moments before the crash. In these rear-end crashes, teenage drivers’ average reaction time was slower when they were on a phone (2.8 seconds) than when they were interacting with passengers (2.1 seconds).

Broadly, these findings are consistent with previous studies on the nature and risks of distracted driving, though the new report adds a trove of video evidence. The findings underscore the risks not just for teenagers but for adults, who while they have more experience behind the wheel are generally no more able than teenagers to have their eyes, hands and minds on a device and simultaneously focus on the road.

The study comes as policy makers and safety advocates have been vexed by the challenges of shaking drivers from what appears to be a widespread state of denial. Most people say that using cellphones, particularly for texting, is dangerous when driving — and many still do it anyway. Safety advocates call this it a case of “do as I say, not as I do” behavior that has proved tenacious given the ubiquity of phones, their growing capabilities, new entertainment systems built into cars and social and business pressures that people feel to stay always connected.

In the case of young drivers, the AAA Foundation for Traffic Safety advocates laws that prohibit all cellphone use by teenagers and restrict the number of passengers in a car “to one nonfamily member for the first six months of driving.”