An observational study of the network-level traffic variables

Simultaneous ground measurements of traffic variables including speed, concentration, and flow over the Central Business District of Tehran have been made to examine the relations among network-wide averages of such variables. The two-fluid model, a curvilinear relation between the trip time and stop time per unit distance, has been calibrated to characterize the quality of traffic service in the study network. In addition, relations between the fraction of vehicles stopped and the average concentration, as well as between the averages of speed and concentration, are derived to describe interrupted traffic flow conditions in urban networks.