It is already known that outside distractions, such as mobile phones, can increase the risk of a car crash. However a new study has found that people whose minds wander while driving may also be responsible for a ‘substantial proportion' of crashes.

According to French scientists, mind wandering refers to times when you think about something that is unrelated to the task at hand. It often occurs during times of rest or during repetitive tasks. Little is known about its role in car crashes.

The scientists decided to analyse this further. They interviewed almost 1,000 drivers attending an ED (emergency department) after a car crash between April 2010 and August 2011.

The participants were asked what they were thinking about just before the crash. The scientists then assessed how distracting these thoughts were. The emotional state of the drivers was also looked at.

Other factors that could have played a role in the crash, such as road conditions and traffic, were also taken into account and the drivers' blood alcohol levels were checked.

Almost half of the drivers who took part in the study were deemed to be responsible for the crash they were in.

Of these at least half said their mind had wandered just before the crash and in 13% of cases, this mind wandering was described as intense - in other words, highly distracting or disruptive.

Overall, those who had experienced intense mind wandering were much more likely to be in a crash which they were responsible for, even when other factors were taken into account.

The scientists concluded that intense mind wandering could make drivers ‘prone to overlook hazards and to make more errors during driving'.

"Detecting those lapses can therefore provide an opportunity to further decrease the toll of road injury," they added.

Details of these findings are published in the British Medical Journal.