Dr. Declan Bedford:

We do not, but we know it is becoming very prevalent and has been recognised in the past ten or 15 years as a serious cause of road crashes. We can sometimes tell what the cause of a road crash is, such as where somebody has been driving, falls asleep and hit something without using the brakes. People who are in a crash when awake slam the brakes on. Somebody may crash into a tree having come off the road and were not paying attention because they fell asleep. The interesting thing is we have all felt tired while driving. Sometimes when we feel tired while driving we open a window, turn the radio up and do other things. They do not work. People have to get out of the car and take a ten or 15-minute break, have a cup of coffee and go for a walk. My car tells me when to take a break.