Model risk homeostasis Wilde

If there is a utility model determining target risk, then it should be feasible to formulate that model in mathematical terms, or alternatively to derive the utilities and trade-offs through the standard game-type approach used in stated preference studies. However, Wilde (1988) denies that it is possible to derive quantitative utilities [T]he target level of risk is thought of as a construct that people arrive at in an intuitive manner, not as the result of explicit calculation of probabilities of particular outcomes and their positive or negative values (p. 443). Thus, we have a model whose main mechanism cannot be verified empirically because it is only an intuitive construct. Therefore, it can be concluded that what we have here is more assertion than model. (For more on risk homeostasis, the reader is directed to Chapter 5.)... 

The best-known motivational model - and the one that has been most frequently challenged — is the risk homeostasis theory of driving behavior. The first formulation of this model was probably Taylor s (1964) risk-speed compensation model, which postulated that drivers adjust their speeds in accordance with the perceived risk. More recently the model has been expanded by Wilde (1998,2002) to include and account for a host of driver behaviors. Because of the controversy it has generated and the research that it has spurred, it will be described here in some detail. According to Wilde, we strive not to minimize risk (or maximize safety), but to reduce (or increase) it to a non-zero level with wdiich we feel comfortable. Because different driving situations have different levels of inherent dangers, we constantly strive to adjust our behavior to maintain a relatively constant risk level. The continuous adjustment process, similar to diat of a room thermostat, is displayed in Figure 3-12. 

Figure 8.2 Wilde s risk homeostasis model of relation between operator behaviour and accident risk.

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