The research found that motorists talking on mobile phones while driving on dual carriageways and motorways were slower and less likely to overtake.
“The average person’s commute is longer because of that person who is on the phone in front of them,” said University of Utah psychology professor Dave Strayer.
“If you talk on the phone while driving, it’s going to take you longer to get from A to B, and slows down everybody else on the road,” explained researcher Joel Cooper, a doctoral student in psychology.
The findings back previous research that using a hands-free phone is as dangerous while driving as using a hand-held phone because it is the conversation itself that is the major distraction.
Earlier studies also found that mobile phone users followed at greater distances, were slower to brake and to regain speed after braking.
Strayer said it was important to show how mobile phone use affects traffic.
“When people have tried to do cost-benefit analyses on whether we should regulate phones, they don’t factor in the cost associated with increased commuting times, excess fuel used by stop-and-go traffic and increased air pollution.”