A method for emission estimation for microscopic traffic flow simulation

Road traffic plays an important role in exhaust gas emissions. Traffic related emissions can be reduced by different traffic control measures like traffic signals in urban areas and Variable Message Signs on motorways. The control strategies aim to harmonize traffic flow and adjust unavoidable congestion in order to minimize fuel consumption and emissions. Since the engine technology of cars is currently changing rapidly (automatic start-stop, increasing fleet of hybrid vehicles and emerging electrical vehicles) fleet emissions are not as predictable as in the past. In order to test the impact of traffic control strategies on traffic related emissions, a research team at the Technical University in Graz developed a simulation toolbox by coupling a microscopic traffic flow simulator (VISSIM) and a microscopic emission model (PHEM). This toolbox allows to simulate different traffic scenarios for urban and interurban road networks and to calculate the related fuel consumption and emissions. Due to the vast amount of data and the complexity of instantaneous emission calculation based on engine maps, modeling of large-scale road networks is computationally very intensive which limits the number of different traffic control scenarios. This paper presents an intermediate calculation step to make a first estimation of the environmental impacts to avoid unessential detailed investigations. This step provides the possibility to decide whether the simulated traffic control strategy has a positive effect on emissions. Based on this decision support modelers are able to identify suitable control strategies for further investigations. The simplified calculation method is based on averaging a vast amount of vehicle trajectory data. Representative trajectories are taken as classifiers for emission calculation to limit this most time consuming step.