A new ban on using mobile phones while driving will apply to hand-held ones only. But hands-free phones also pose a major risk. Elaine Mulcahy reports

You see it nearly every day. The woman in her jeep negotiating a roundabout with the mobile phone up to her ear; the young man failing to stop at a red light as he turns while talking into a hand-held phone.

The dangers are obvious: if your eyes are diverted to the phone instead of the road while you are driving, you will miss on-coming traffic, road signs, and sudden changes in the conditions ahead. Similarly, you are more likely to have an accident if you are driving using one hand.

Most restrictions on the use of mobile phones in cars, including the long-awaited ban due to come into effect here this autumn, apply only to hand-held mobile phones. It has been assumed that speaking on a hands-free phone is safe - similar to speaking to a passenger.

But recent evidence suggests that enforcing penalties for motorists using hand-held phones, and not hands-free phones, is only tackling half the problem. It is like putting health warnings only on packets of full-strength cigarettes and saying that it is OK to smoke low-tar ones.

Several studies report that simultaneously controlling a car and speaking on a mobile phone seriously impairs driving ability.

The Transport Research Laboratory in the UK found that driving behaviour is more impaired during a phone conversation than driving at the legal alcohol limit (80mg/100ml). Other studies estimate that the risk of collision while using a mobile phone is increased fourfold, while the risk of a fatality is increased ninefold.

David Strayer, a psychologist at the University of Utah, says, "When a caller talks on a phone, they enter a virtual reality" - what he calls "the phone zone" - and pay less attention to their driving. He says this is the case for all mobile phones, including hands-free ones.

Strayer and his colleagues have demonstrated in driving simulation studies that reaction to braking by vehicles in front, detection and reaction to traffic lights and memory for billboards are all impaired when a person speaks on the phone - whether it is hand-held or hands-free. Even when drivers look directly at objects, such as road signs, they often fail to "see" them because their attention is diverted by the mobile phone.

But is speaking on a hands-free phone not the same as talking to a passenger? Strayer says a conversation with a passenger is very different. "Both the driver and the passenger are aware of the driving situations and modulate their conversation based on driving difficulty. When driving becomes more difficult, they put their conversation on hold," he says.

In contrast, drivers often attempt to continue with phone conversations despite increasingly complex traffic conditions.

Also, passengers are often known to help the driver, calling out when they see a car in front brake suddenly, for example. The person on the other end of the phone obviously can't respond to the driver's environment in the same way.

Strayer also says that people who use mobile phones while driving have a false sense of confidence.

His studies found that motorists rarely believe their own driving had been hampered by mobile phone use, even though they could see how other motorists' driving was affected.

A survey by the RAC gave similar results. It reported that 90 per cent of drivers questioned could see that mobile phone use caused other drivers to drive badly. Only 43 per cent believed their own driving was impaired.

"Because people are not processing all the information that they typically would if they were not on the phone, they are unaware of their own impaired driving," adds Strayer.

It is up to people to accept the evidence that speaking on a mobile phone while driving is dangerous and move into a parking zone before entering the phone zone.