Voice-controlled texting and other hands-free tools may seem like safe options for using a cellphone while driving, but one researcher warns that the brain can't safely manage both tasks at once.

New car models increasingly feature built-in hands-free technologies, but they may not cut out the risk of distracted driving; worse, these tools may give motorists a false sense of security, said Robert Rosenberger, an assistant professor and researcher at Georgia Tech's School of Public Policy.

"People who see and use these new technologies may think, 'Now I don't have to look at my phone. And the technology is built right into the car, so it must be safe,'" Rosenberger said. "But, just like state laws that prohibit handheld phone use and mandate hands-free use, they don't actually eliminate the distraction. In fact, one could argue that they encourage continued distractions." [The 10 Best Hands-Free Car Kits]

Laws banning cellphone use while driving are often centered around the assumption that mobile devices pull drivers' eyes off the road — and those dangers are real. One recent study found that a three-second distraction, such as glancing down at a phone, can double the number of mistakes people make behind the wheel.

But Rosenberger argues that the phone itself can also be a stand-in for a more nebulous distraction: the conversation. The physical phone may fade into the background of the user's awareness, much like eyeglasses on the face, he explained in an article in IEEE Technology & Society Magazine. The focus instead switches to the person on the other end of the call.

"When a person talks or texts on a phone, they go into a zone and everything around them seems to fall into the background of awareness," Rosenberger said in a statement from Georgia Tech. "For instance, you no longer hear the TV that you were watching seconds before the phone rang. Walls and adjacent objects seem to disappear. The only thing you concentrate on is the other person's voice."

Rosenberger points to studies showing that phone usage — handheld and hands-free alike — can lead to a significant drop in driving performance. One study in 2006 even found that motorists who talk on cellphones while driving are as impaired as drunk drivers.

Conversations taking place in the car, meanwhile, may be less dangerous. A 2008 paper in the Journal of Experimental Psychology found that people can more easily manage driving and having a conversation with a passenger than with someone on the phone. That's because when a driver and passenger are talking in a car, the complexity of their conversation tends to adjust with the traffic situation, those researchers said.

"If two people are talking in a car and an ambulance approaches, they tend to stop speaking and look for the sirens," Rosenberger said. But a person on the other end of a cellphone call is not aware of the changing situation on the road, he added.

Rosenberger says policymakers should consider these hazards when creating distracted driving laws, and he recommends that drivers should refrain from cellphone communications behind the wheel, even hands-free alternatives.

"My suggestion: Use your drive time to unplug from the digital world," he said.

His arguments are outlined in both the Communications of the ACM and IEEE Technology & Society Magazine.

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