Task difficulty and risk in the determination of driver behaviour

The task-capability interface (TCI) model provides a theoretical formulation that enables integration of the competing concepts of Wilde's risk homeostasis theory (Wilde, G.J.S., 1982. The theory of risk homeostasis: implications for safety and health. Risk Analysis 2, 209-225) and the zero risk theory of Naatanen and Summala (1976). The model proposes that drivers opt for a range of task difficulty they are prepared to accept and modify their speed in particular to maintain that level. Three predictions from the TCI model are that perceived difficulty should be systematically related to speed, that ratings of the likelihood of collision (i.e. statistical risk) should be independent of speed until task demand approaches capability and that feelings of risk should correlate with ratings of statistical risk. These predictions were tested in two experiments using 70 licensed participants (M = 24.7 years) who rated segments of three types of road driven at different speeds in a video simulation of the driving task, filmed from the driver's perspective. The results of both experiments supported predictions from the TCI model that task difficulty ratings would be highly correlated. with speed and that estimates of statistical risk would be independent of speed until the driving task became more demanding. However, ratings of perceived risk were completely independent of estimates of statistical risk at lower speeds, but were highly correlated with ratings of task difficulty throughout the range of speeds studied. Thus the experience of risk is not the same as. subjective estimates of the probability of collision. It was concluded that feelings of risk may provide the motivational dimension for avoiding taking on a level of task difficulty which is too high. (C) 2006 Elsevier Masson SAS. All rights reserved.