Calibration of flow-density relationships on urban streets

The aim of this paper is to gather some observations resulting from the study of traffic data in an urban environment (Toulouse, France) rather than on freeways, as is often the case in papers that deal with flow-density relationship calibration. Methods developed for freeway data are studied and new ones are presented to address the specificity of traffic behavior in urban areas. A two-step approach is proposed. First, the data are processed to obtain consistent observations for simulation use. This processing includes the calculation of density from occupancy and space mean speed and the aggregation and the selection of data to make them suitable for equilibrium traffic state representation. Then, a best-fit curve is applied to the selected data to obtain flow-density relationships. Finally, the resulting relationships are studied to highlight the peculiarities of traffic behavior in urban streets.