Developing Passenger Car Equivalents for Freeways by Microsimulation

In this paper a method of estimation of the passenger car equivalents for heavy vehicles on freeway is described. The variation in traffic quality was evaluated basing on a traffic demand characterized by different percentages of heavy vehicles. Aimsun micro-simulator was used to isolate traffic conditions difficult to capture on field, to replicate them to have a number of data as much as possible numerous, and to quantify the fundamental variables of traffic flow, namely the speed, flow, density, for a test freeway segment. Model calibration was accomplished by using traffic data collected at observation sections on the A22 Brenner Freeway, Italy. In order to check to what extent the model replicated reality, the validation of the calibrated model was also addressed. Simulation data were used to develop the relationships among the variables of traffic flow and to calculate the passenger car equivalents for heavy vehicles by comparing a fleet of passenger cars only with a mixed fleet characterized every time by different percentages of heavy vehicles. Despite the exploratory nature of this study, some implications can be drawn: PCE estimations are small at low flow rates and increase with increased flow rates due to at low volumes there are few passenger cars that can be influenced by heavy vehicles.