Earlier studies concerning subjective judgement of filmed traffic conflicts demonstrated an internal concept of dangerous level. In the present study, two experiments were carried out to investigate the concept further. Since several conflict observation techniques incorporate the impetuosity of an evasive action during a conflict, the relation between impetuosity and dangerous level was investigated.Although the impetuosity of a conflict predicts the dangerous levelof a conflict rather well, it was concluded that the information underlying the judgements differed. In the second experiment the same filmed conflicts were divided into a commencement and a manoeuvre stage and judged on a scale of dangerous level. By relating the judgements of the different stages and the overall judgements, the information of relevance for the concept 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 dangerous level of a conflict. It was concluded that the concept of dangerous level 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.
Abstract