The subjective evaluation of traffic conflicts based on an internal concept of dangerousness.

Earlier studies concerning subjective judgement of filmed traffic conflicts demonstrated an internal construct of dangerousness. In the present study, two experiments were carried out to investigate the construct further. Since several conflict observation techniques incorporate the impetuosity of an evasive action during a conflict, the relation between inpetuosity and dangerousness was investigated. Although the impetusoity of a conflict predicts the dangerousness of a conflict rather well, it was concluded that the information underlying the judgements differed. In the second experiment the same filmed conflicts were partitioned into a commencement and a manoeuvre stage and judged on a scale of dangerousness. By relating the judgements of the different stages and the overall judgements, the information of relevance for the construct was examined. The results showed that the last part of the conflict, the part that contains most information about the minimal Time to Collision and about the Minimal Distance is of no relevance for judging the dangerousness of a conflict. It was concluded that the construct of dangerousness is based on information contained by the commencement of a convergence and by the onset of an evasive action. Finally, a conjunctive model, explaining the contribution of the two stages to the decision making process, is presented.