Although evidence concerning the dangers of using a cellphone while driving has been available for many years, New Zealand still has no explicit legislation in this area.

Somewhat belatedly, the Government is considering a law change that would make it illegal to use a hand-held cellphone while driving. But it is also proposed that using a hands-free phone while driving should remain legal.

The main thrust of this measure is welcome. Several tragic and widely publicised accidents involving young drivers who were text messaging while behind the wheel have highlighted the catastrophic consequences of this dangerous behaviour.

At first sight, an exemption for hands-free phones also appears to make good sense. Surely using hands-free is no more dangerous than talking to someone in the passenger seat? A substantial body of research now supports the surprising conclusion that using a hands-free phone while driving is no safer than using hand-held.

In an influential study by researchers at the University of Toronto, cellphone records of drivers who had been involved in collisions were examined.

Using a cellphone while driving was linked to a four-fold increase in the risk of having an accident.

Interestingly, their results failed to provide the slightest hint that hands-free phones might be less risky than hand-held. A recent Australian study reported closely similar findings.

Several studies carried out at the University of Utah examined effects of using a cellphone on driving in a simulator. Substantial impairments were observed - and there was no difference between hands-free and hand-held phones.

In one experiment, cellphone drivers were compared with drunk drivers, who had a blood alcohol level at the legal limit. Cellphone drivers were slower to start braking and had more simulator accidents than either intoxicated drivers
or drivers in a neutral control condition. Once again, drivers using hands-free were just as impaired as drivers using hand-held phones.

A study carried out at Stockholm University examined real driving on a motorway. Using a cellphone while driving impaired the ability to detect peripheral visual signals - and yet again, there was no difference in the degree of impairment produced by hands-free and hand-held phones.

Evidence from all three research sources - analysis of accidents and phone records, driving in a simulator, driving on a real road - is consistent and points to the same conclusion. Talking on a hands-free phone while driving is just as dangerous as using a hand-held phone.

It appears that the conversation itself is the vital factor, rather than the physical demand of holding and manipulating the phone. Interestingly, the same impairments are not seen when a driver converses with a passenger who is physically present.