An introduction is given to our psychophysical response and valence theory of choice behaviour, since the risk-adaptation theory derives from that theory as an application. Risk-adaptation theory assumes that road users implicitly evaluate their risks by oppositely oriented, single-peaked valence functions of arousal and fear sensations as dependent aspects of risks in road traffic. Due to this dependence and the adaptation to changing risk levels, these single-peaked valence functions combine additively to a dynamic shifting interval of ambivalent risk indifference, where above and below the risk evaluation is increasingly negative. Risk-adaptation theory contains the zero-risk, threat-avoidance, and risk-homeostasis theories asspecial cases and predicts that: (1) fatality risks decay exponentially, (2) the slope parameter for the exponential fatality risk decay is 11/2 larger than for the traffic growth function, (3) a safety measure with a very large effect will be initially compensated to a lesser low risk level thanotherwise expected, and (4) the contributions of a road safety measure todanger perception and arousal level determines whether its expected safety effect will be reinforced or adversely compensated. Each prediction is tentatively verified by some research. (A) Reprinted with permission from Elsevier.
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