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Phone conversations in cars are dangerous whether or not they are conducted hands-free, a study suggests.
The findings make the case for all phones, including hands-free sets, to be banned from motor vehicles, according to the scientist who led the research.
Volunteers asked to react to simulated driving hazards performed poorly when they were distracted by a voice engaging them in conversation.
They took just under a second longer to respond to events such as a pedestrian stepping off the pavement, an oncoming car on the wrong side of the road, or an unexpected vehicle parked at a junction.
Compared with having no verbal distraction, they also detected and reacted to half as many hazards.
Dr Graham Hole, senior lecturer in psychology at the University of Sussex, said: “A popular misconception is that using a mobile phone while driving is safe as long as the driver uses a hands-free phone.
“Our research shows this is not the case. Hands-free can be equally distracting because conversations cause the driver to visually imagine what they’re talking about. This visual imagery competes for processing resources with what the driver sees in front of them on the road.”
He added: “At the moment the law sends out the wrong message that hands-free phones are safe. If you stop at a motorway service station you can see shops selling hands-free kits with the slogan ‘be safe, be hands-free’.
“It’s a tricky one. The problem is enforceability – it’s very difficult for the police to tell if someone’s using a hands free phone. But on balance, I think the law should be changed to get the right message across and make it absolutely clear that any use of a mobile phone while driving is hazardous.”
The study involved 20 male and 40 female participants who took part in video tests while sitting in a car seat behind a steering wheel.
At their feet were two pedals, representing a brake and accelerator. Each volunteer was shown a series of seven-minute films showing real life driving scenes during which unexpected hazards appeared that required them to respond by hitting the brake. Like the steering wheel, the accelerator pedal only acted as a prop.
One group of volunteers were allowed to “drive” undistracted while another two heard a male voice from a loudspeaker three feet away make statements they had to decide were true or false.
Half the “distracted” participants were given statements that involved little visual imagery – for instance, “leap years have 366 days”. The rest had to consider visually stimulating statements, such as “a £5 note is the same size as a £10 note”.
Eye tracking technology monitored where volunteers were looking when they reacted to hazards.
The results showed that people were significantly worse at responding to emergencies on the road when distracted by a voice talking to them from a loudspeaker. Those having to exercise their visual imagination performed worst of all.
“You are 0.98 of a second slower to respond to hazards if you’re on a hands-free mobile phone than if you’re not,” says Dr Hole.
“That doesn’t sound like much, but at 30mph you’re travelling at 13 metres per second. You require a stopping distance equal to three-and-a-quarter Ford Fiestas.”
Drivers distracted by hands-free phone conversations also focused on a small area of road and failed to spot hazards even when they looked at them, the study published in the journal Transportation Research revealed.
“Eye tracking shows that their eyes are falling on the hazard but they’re not reacting,” said Dr Hole. “The eyes are there but the brain’s away.”
