Behavioural effects of mobile telephone use during simulated driving

The effects on driving performance of using a hands-free, mobile telephone were investigated in a pursuit-tracking task that simulated driving. Twenty subjects in two age groups, 19-26 years (median = 21 years) and 40-51 years (median 45·5 years), participated, with five males and five females in each group. The primary task was driving safely. The subjects drove for 20 min in each of three secondary task blocks with (i) a simple telephone conversation about a familiar topic, (ii) a difficult telephone conversation, incorporating a test of working memory, and (iii) car radio tuning and listening. Half of the driving was done on a simulated firm road surface and half on a slippery road surface. The subjects behaviour was subsequently observed and classified in four activity categories, two without and two with a secondary task, with driving (i) on a clear road, and (ii) with obstacles, and with driving involving the secondary task components of (iii) communication, and (iv) instrument manipulation. The results show different patterns of driving performance on the two road surfaces. For driving on the slippery road, a deterioration was especially marked during manipulation of the instruments, in particular the radio, which required more prolonged manipulation than the hands-free telephone. Driving during an easy telephone conversation was associated with the least performance decrement, and could, in some cases, be seen as facilitatory. The female subjects tended to perform less well than the male subjects while driving on a slippery road. Some of this difference could be attributed to less previous driving experience. In general, the male drivers exhibited better control while driving under difficult conditions. There was no difference in driving proficiency between the age groups. It is concluded that simply conversing over a hands-free telephone while driving does not in itself impair performance. However, a difficult conversation may affect the driving adversely, and any prolonged manipulation of the telephone is liable to produce a performance decrement, particularly under conditions that put heavy demands on the driver's attention and skill.