Emissions estimation for obsolescing bus fleets. Problems and advances

When it comes to simulate traffic emissions, problems arise: which is the best model to use, which data are needed and whether they are all available, whether the process is time-consuming and/or calls for expert, etc. It is not surprising, then, that public transport operators might be hesitant in estimating the emission package of the bus fleets they manage. Moreover, the underestimation of the local fleet potential in producing pollution (in case of small fleets) on the one hand, and the reluctance to estimate it when the fleet is composed by a good amount of old-generation vehicles on the other, are further elements of uncertainty. However, transit operators’ obligation to manage and maintain clean bus fleets is becoming more and more imperative and in Italy recent regulations subsidize transit companies to purchase buses with cleaner performance. The assessment of how much pollutant is the fleet to renovate becomes, then, crucial. To this end, an emission-estimation model for bus fleets is developed and described in the paper, with the research goal to facilitate the emissions calculation among transit operators. The procedure is embedded in an already successfully-implemented software for the management and maintenance of bus fleets. The model moves from well-known assessment methods (namely COPERT and IVE) but addresses issues like long-protracted mileage and age of vehicles which make it especially useful when “old” fleets emissions are to be assessed. A case study, in a middle-size city in Italy, is also described to highlight the model development