A sensitivity study of road transportation emissions at metropolitan scale

International audienceRoad traffic transportation emissions depend on both the traffic flow and the vehicles emission factors. They are very sensitive to the input data of both traffic assignment models and emissions calculation methods. In this study, we investigate the influences of the input data on a simulation chain from traffic flow assignment to emissions calculations, based on a case study in the agglomeration of Clermont- Ferrand in France. In order to better represent the congestion phenomenon and the temporal and spatial evolution of traffic flow, we use a dynamic traffic assignment model, LADTA, to compute the traffic flow at street resolution. The model is evaluated by comparison between model predictions and traffic flow observations captured by inductive loop traffic detectors. The traffic flow outputs of LADTA are then coupled with COPERT model to calculate emissions of air pollutants(nitrogen oxides NOx for example). A sensitivity study is then carried out by varying the input parameters in the traffic emission modeling chain: the total traffic volume injected into the network, the average speed, the vehicle fleet composition, etc. The study shows that the emissions are very sensitive to these factors, especially during the transition from a free traffic network to a congested one