A Preliminary Study to Evaluate Emissions Factors by Real and Micro Simulated Driving Cycle

Transport activities contribute significantly to the air pollution and its impact on emissions is a key element in the evaluation of any transport policy or plan. Calculation of emissions has therefore gained institutional importance in the European Community. To obtain emission factors several methods make use of only vehicle mean velocity, which can be easily obtained by vehicle flow and density in the road. Among them it is worth mentioning COPERT IV (Ntziachristos et al.,2006), MOBILE (US EPA, 2006), INFRAS (Keller et al., 2004), MEET (Joumard et al.,1999) models that are widely used in the practice. It is possible to refine the calculations by applying some correction factors to take into account the effect of specific elements (cold start, new technology, age of vehicle). Recently in ARTEMIS project (Joumard et al., 2007), a new statistical approach has been developed capable to consider more attributes than the simple mean speed to characterize driving behaviour, not only in the determination of driving cycles but also in the emission modelling. In this context, a meso scale emission model, named KEM, Kinematic Emission Model, able to calculate emission factor was developed by Rapone et al. (2005-2007). However, it is necessary to consider that the input to this model is, in any case, the driving cycle, and that developing a quantitative method capable to determine on the basis of road characteristics and traffic management rules, the exact mix of driving cycles results a very hard job. A possible approach to face this issue is represented by the use of microscopic traffic simulation models. In particular, for each specified road and related traffic conditions, micro-simulation models can determine instantaneous kinematic features of each vehicle moving on the simulated transportation network, thus providing the needed input quantities of emission models. Therefore they could be used to extract some representative traffic situations and real driving cycles (DCs), avoiding the very expensive costs of experimental campaigns needed to obtain driving cycle really representative of driving behavior. Key issue of the whole approach is the reliability of traffic generated by simulation models. For such a reason this preliminary study aims at testing the capabilities of four well known car-following models (which represent the very basis of any microscopic traffic simulation tool) at reproducing real life trajectories and then at checking the errors introduced by using the simulated trajectories, in the place of the real ones, for calculating traffic emissions by means of the KEM emission model.JRC.H.4-Transport and air qualit