Notice that the final decision is defined by both probability and the cost function, for the vehicle-vehicle interactions, the cost function of the ego vehicle is given in Note S4, Supporting Information.

Aggressiveness Estimation and Belief Updating

The road-user's decision is based on her/his observation of the aggressiveness of the surrounding road-users. Aggressiveness is defined as a trade-off between safe distance and travel efficiency. Based on this definition, the observed aggressiveness is given by a sum of the longitudinal and lateral components, which aligns with the research of risk field: driver's reaction to the surrounding obstacles is a function of relative distance. Meanwhile, we also have to mitigate the part of distance variations that the subject driver generates. The risk field is simplified with the Gaussian model as in (5) where the parameters of the risk field can be obtained via the proposed experiments.