In another study, they examined voice-dialing, voice-contact calling and music selection using in-vehicle information or "infotainment" systems in 10 model-year 2015 vehicles.
Three were rated as moderately distracting, six as highly distracting and one as very highly distracting, the US-based traffic safety non-profit said in a report.
"Just because these systems are in the car doesn`t mean it`s a good idea to use them while you are driving," said senior author of the two studies David Strayer, psychology professor at University of Utah.
"It is better not to use them when you are driving," Strayer said.
The research also found that, contrary to what some may believe, practice with voice-recognition systems does not eliminate distraction.
But the most surprising finding was that a driver traveling only 25 mph continues to be distracted for up to 27 seconds after disconnecting from highly distracting phone and car voice-command systems, and up to 15 seconds after disconnecting from the moderately distracting systems.
The 27 seconds means a driver traveling 25 mph would cover the length of three football fields before regaining full attention.
"Most people think, `I hang up and I`m good to go,`" Strayer said.
"But that`s just not the case. We see it takes a surprisingly long time to come back to full attention. Even sending a short text message can cause almost another 30 seconds of impaired attention," Strayer said in a statement released by University of Utah on Wednesday.
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