The University of Utah psychologists Frank Drews, David Strayer and Monisha Pasupathi found as young adults talk on cell phones while driving, their reaction times become as slow as reaction times for senior citizens.
During the study, the researchers used sophisticated driving simulator and found that when drivers talk on a cell phone, they drift out of their lanes and missed exits more frequently than drivers conversing with a passenger.
Previous studies by Strayer and Drews have found that hands-free cell phones are just as distracting as handheld models because the conversation is the biggest distraction. Drivers talking on cell phones are as impaired as drivers with the 0.08 percent blood alcohol level that defines drunken driving in most states.
Strayer said he often is asked about the distraction caused by conversations with passengers versus people on the other end of a cell phone, "because in both cases you have a conversation."
He found that turns out that a driver conversing with a passenger is not as impaired a driver talking on a cell phone.
"The passenger adds a second set of eyes, and helps the driver navigate and reminds them where to go," said Strayer, a professor of psychology at the University of Utah and a co-author of the study.
"You see bigger lane deviations for someone talking on a cell phone compared with a driver talking to a passenger.
"You also find when there is a passenger in the car, almost everyone takes the exit. But half the people talking on the cell phone fail to take the exit," he added.
"The difference between a cell phone conversation and passenger conversation is due to the fact that the passenger is in the vehicle and knows what the traffic conditions are like, and they help the driver by reminding them of where to take an exit and pointing out," Strayer added.
The study will be published in the Journal of Experimental Psychology: Applied.