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Safety performance measures can be obtained either through simulation (based on well specified or calibrated traffic models) or experimentally through observational vehicle tracking data. Accurate calibration of traffic models ensures that simulated measures of safety performance are reflective of “real world” traffic conditions. The microscopic model, for a case study, allows the estimation of road safety performance through a series of indicators, representing interactions in real time between different pairs of vehicles belonging to the traffic stream. When these indicators reach a certain critical value, a possible accident scenario is identified. For the same case study, safety performance indicators are obtained through a video image processing algorithm for vehicle detection and tracking. The accuracy of the algorithm is evaluated with respect to GPS tracking measurements. The algorithm adopts a background …