An integrated framework of real and micro simulated driving cycles to evaluate a new emissions factors model 2011-01-2063
Transport activities contribute significantly to air pollution. For this reason any policy or plan, carried out by administration or institution, requires the assessment of its impact on the emissions. To assess the overall pollutant production from transport, it is necessary to calculate emission factors. For this aim several methods exist which only use the average speed of the traffic stream, which can be theoretically obtained by vehicles flow and density on the road.
Recently, 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. However, it is necessary to consider that the input to this model is, in any case, the driving cycle. A possible way of gathering such detailed data is represented by the use of microscopic traffic simulation models. In particular, per each simulated traffic scenario, micro-simulation models can determine instantaneous kinematic characteristics of each vehicle moving on the simulated transportation network, thus providing the needed input quantities to the emission models.
Key issue of the whole approach is, however, the reliability of traffic generated by simulation models. For this reason the study aims at testing the capabilities of four car-following models (at the basis of any microscopic traffic simulation tool) at reproducing real vehicles trajectories and then at checking the errors introduced by using the simulated trajectories, in place of real ones, for calculating traffic emissions by means of the KEM model. Finally the emission behaviors of the simulated trajectories were analyzed through several experimental tests performed on a chassis dynamometer bench for characterizing regulated emissions and fuel consumption. Tests were also compared with predicted emissions of the conventional Euro 4 gasoline technology provided by KEM - and by the COPERT 4 model.