Hands-free devices intended to keep drivers more focused on their driving may not be as safe as previously thought.

A new study by the AAA Foundation for Traffic Safety released Thursday found that it can take 27 seconds for a driver using a car's voice-activated system or smart phone to regain full alertness after making a voice command from behind the wheel.

And that means at the 25 miles per hour speed limit in the study, drivers traveled the length of nearly three football fields before regaining their focus.

"The lasting effects of mental distraction pose a hidden and pervasive danger that would likely come as a surprise to most drivers," said Peter Kissinger, President and CEO of the AAA Foundation for Traffic Safety. "The results indicate that motorists could miss stop signs, pedestrians and other vehicles while the mind is readjusting to the task of driving."

AAA, in conjunction with researchers at University of Utah, tested 257 drivers between the ages of 21 and 70 using the voice-activated technology in ten 2015 model vehicles. The study also tested 65 additional drivers between the ages of 21 and 68 using three types of smartphone systems.

The analysis found that all systems studied increased mental distraction to potentially unsafe levels.

Researchers rated driver distraction on a scale of 1 to 5, with 1 being relatively safe, about equal to listening to the radio, and 5 being highly challenging in such a way as to overload the driver's attention.

The best performing systems were the Chevy Equinox and Buick Lacrosse, both with a cognitive distraction rating of 2.4, while the worst performing system was the Mazda 6 with a cognitive distraction rating of 4.6.

The systems that performed best generally had fewer errors, required less time on task and were relatively easy to use.

The researchers also studied voice-activated smartphone technology and found that Google Now outperformed Apple Siri and Microsoft Cortana but, they say, all were dangerously distracting with ratings of 3.1, 3.4 and 3.8 respectively.

This research represents the third phase of the AAA's comprehensive investigation into cognitive distraction, which shows that new hands-free technologies can mentally distract drivers even if their eyes are on the road and their hands are on the wheel.

The National Highway Traffic Safety Administration said that in 2013 there were 3,154 people killed and an estimated additional 424,000 injured in motor vehicle crashes involving distracted drivers.

Connecticut's Department of Transportation does not collect data on accidents caused by distracted driving.

"Automakers often promote everything their connected cars can do, but this research paints a frightening picture of what drivers can't do if they use the popular features," said AAA spokeswoman Amy Parmenter. "Hands free does not mean risk free. It's that simple."

i.larraneta@theday.com

Twitter: @larraneta