Trajectory-based indicators to determine the local character of intersection conflicts: A micro-spatial analysis.

Real world behaviour data is the most reliable reference to assess road safety in a specific road infrastructure context. However, its collection and implementation for road safety research in a rapid and portable manner is still challenging, facing data protection issues and the complexities to set up constant tracking mechanisms with their own power supply. To tackle these limitations, the Mobility Observation Box (MOB) provides a flexible data collection, to be used in subsequent video analysis. Object detection and tracking allow for the derivation of movement trajectories, which in turn allow to derive quantitative indicators of road safety relevant behaviour, namely well-established Surrogate Safety Measures (SSMs), such as Post-Encroachment-Time (PET), Time-to-Closest-Approach (TCA) and Time-to-Collision-(TTC) alongside a number of indicators like maximum speed of two interaction partners, the angle they approach each other in and the minimum distance they had at one point in their interaction. To facilitate potential MOB uses, this study leverages over 51 h of naturalistic video data at a busy Vienna intersection to advance road safety research by (i) employing random parameters binary modelling of the likelihood of critical conflict occurrence and (ii) Gaussian generalized additive spatial modelling to identify key factors influencing the absolute values of conflict angles on critical conflicts only. Within the examined intersection, specific speed and acceleration effects were determined, together with the respective heterogeneity-in-means, as well as significant categorical effects of different road user types. All road user types were ultimately less likely to be involved in safety-critical conflicts compared to cars in both leading (firstly detected) and following (secondly detected) roles, with the exception of cyclists in the leading role. Within the micro-spatial analysis, the kinematic parameters of the second road user only (speed, max acceleration and max deceleration), the duration of the interaction as well as intersection-specific local effects related to the position of the leading road user were all found to influence the transformed absolute value of the angles of critical conflicts.