>>> we are back with new research on the problem of distracted driving. we've all been encouraged to go hands free when using the phone behind the wheel. researchers at aaa and university of utah say the distractions could be just as great with that, tom costello took a test drive .
>> reporter: the first in-depth study of driver's brain activity while they drive.
>> minus y --
>> reporter: from performing math equations to dictating an e-mail.
>> hey, tyler, let's do it again.
>> reporter: the more we have on our minds, the less we pay attention to driving, even when our hands stay on the wheel.
>> the neurosignature is suppressed because are you paying attention to the phone call rather than driving.
>> reporter: researchers put me through some of the paces, including brainy electrodes and cap. it began with a simple drive with the radio on. every time i saw a green light , i had to press a button with my thumb.
>> sometimes as mental workload increases, people are more likely to miss those green lights.
>> reporter: for most people, driving with the radio on isn't a big distraction, but when i have to listen to and dictate text messages hands free ?
>> coming in june.
>> which band is coming to town and what day? 10% slower responding to the green light .
>> oh, stop sight. sorry, guys.
>> we don't react as quickly. miss visual cues like stop signs.
>> reporter: distracted thriving thought to play a role in 30% of all accident.
>> our research shows that interacting with hands free still causes driver distraction.
>> reporter: aaa believes hands free technology should only work with the car in park. tom costello, landover, maryland.
>> reporter: the first in-depth study of driver's brain activity while they drive.
>> minus y --
>> reporter: from performing math equations to dictating an e-mail.
>> hey, tyler, let's do it again.
>> reporter: the more we have on our minds, the less we pay attention to driving, even when our hands stay on the wheel.
>> the neurosignature is suppressed because are you paying attention to the phone call rather than driving.
>> reporter: researchers put me through some of the paces, including brainy electrodes and cap. it began with a simple drive with the radio on. every time i saw a green light , i had to press a button with my thumb.
>> sometimes as mental workload increases, people are more likely to miss those green lights.
>> reporter: for most people, driving with the radio on isn't a big distraction, but when i have to listen to and dictate text messages hands free ?
>> coming in june.
>> which band is coming to town and what day? 10% slower responding to the green light .
>> oh, stop sight. sorry, guys.
>> we don't react as quickly. miss visual cues like stop signs.
>> reporter: distracted thriving thought to play a role in 30% of all accident.
>> our research shows that interacting with hands free still causes driver distraction.
>> reporter: aaa believes hands free technology should only work with the car in park. tom costello, landover, maryland.