Fitting Time Headway–Vehicle Speed Bivariate Distributions: An Operational Procedure For Two-Lane Two-Way Roads

Knowledge of traffic flow characteristics at cross-sections helps analysts, software developers and practitioners to identify, model and simulate traffic flows as inputs in operational analysis. This work presents a complete procedure for constructing bivariate time headway-vehicle speed distributions starting from raw traffic data on two-lane two-way roads. The general framework of the procedure, together with functional components and their mutual interactions, was designed and implemented. The effect of flow rate in both directions (analysed and opposite) on time headway and vehicle speed distributions was analysed. The possibility of associating the time headway-vehicle speed probability density function with several kinds of traffic conditions in both directions/lanes is a significant and interesting advance with respect to previous works. The procedure was applied to a set of four cross-sections belonging to the road network of the Province of Venice (north-east Italy). This application enabled the applicability of the various steps of the procedure to be tested, for better knowledge of how the findings can be used for traffic flow description and simulation.