This paper introduces a framework to model vehicle-bicycle interactions at unsignalized roundabouts. Based on discrete choice theory, a probabilistic model of two hierarchical levels is proposed to represent the driver yielding decision process. The first level models the probability of conflict whereas the second level quantifies the probability of yielding given that a conflict has occurred. A case study is introduced for evaluation of the proposed methodology using real data observed at a typical Swedish roundabout. The results show that the conflict probability is influenced differently depending on the user, cyclist or driver, arriving to the interaction zones. The yielding probability is negatively correlated with the speed of the vehicle when the driver makes decision. The model estimation results also suggest that the relative position of bicycle has larger impacts than its speed i.e. the closer the bicycle is to the conflict zone the greater the impact is on the driver decision. Finally, the empirical analysis also indicates that vehicle speed less than a threshold value shall lead to a high yielding rate, and therefore safer situation at the roundabout. (Author/publisher)
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