Scientists at the University of Sussex have found that drivers using a hands-free phone get just as distracted as those holding it in their hand.

The study revealed conversations can cause the driver to visually imagine what they are talking about, using up part of the brain normally spent watching the road.

The 60-strong study involved 20 male and 40 female drivers who took part in video tests while sitting in a car seat behind a steering wheel. One group of volunteers were allowed to “drive” undistracted while another two heard a male voice from a loudspeaker 3ft (0.9m) away. Those who were distracted by the voice 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.

The study also showed that asking a simple question, such as “Where did you leave the blue file?” during phone conversations could mean a driver concentrates on an area four times smaller than normal, because their brain is imagining the room where they left the file, instead of checking for hazards in front of them.

This research is important because, anecdotally, we all know its true that you cannot place 100% concentration on both driving and a telephone conversation. How many of you have been on the phone and forgotten where you are, perhaps unsure of what the next motorway junction is or what road you’ve joined? How frequently have you come off a hands free call and then realised you couldn’t recall some of the things you discussed?

For a sales person this could be pretty important. Did we agree a 10% discount or 20%? When did I say I’d go and see that client next? What product did they just order?

Back in my days as a driver trainer, we used to take drivers onto a private airfield, get them to drive through a course made out of traffic cones and phone them ‘hands-free’ while they were doing it. We’d then enter into a conversation consisting of 10 questions about product details, costs, timings and we even asked some basic questions such as the address of their office.

Not only did drivers frequently hit the cones, I can’t recall a single person getting 10 out of 10 on the questions, the criteria being they answered correctly or could remember what they agreed to after they got out of the car.

The harsh reality is, we’re kidding ourselves if we think this is safe practice and that it’s productive for someone to use a hands-free phone while driving. I saw a talk recently when a business owner said, ‘One hour of uninterrupted thinking time was better for his business than a month of meetings, emails and telephone calls’.

If this new research by the University of Sussex doesn’t sway you, maybe that’s a good reason to switch your phone off completely when driving!