Anomalous noise events considerations for the computation of road traffic noise levels: The DYNAMAP's Milan case study

Dynamic noise maps are computed to represent the noise levels generated by road traffic in real time to determine the population exposure to environmental noise. To this aim, a network of acoustic sensors can be deployed in representative street locations to capture and process raw acoustic data before estimating the equivalent noise levels (L_eq) of the maps. In the framework of the DYNAMAP project, we conducted a study of the acoustic levels of several streets to determine the most suitable places for the sensors to be deployed in the case study of Milan city. The conclusions of that analysis were that the streets under test could be described by two different time-dependent behaviors, instead of the functional classification of roads. For a proper evaluation of the equivalent value L_eq, several acoustic events existent in the street measurements have to be removed, since they are not generated by road traffic noise. These events, denoted as anomalous noise events, can come from sirens, horns, noisy human activities, etc. To that effect, the measured acoustic signal in the street has to be studied to classify whether the sample belongs to regular road traffic noise, or it is an anomalous noise event, assuming that the typology of these events is very diverse. In order to allow the deployment of the monitoring system, this evaluation should be conducted previously, and if possible, in the acoustic sensor sites resulting from the previous analysis. In this paper, we evaluate the different typologies of anomalous noise events observed in the city of Milan and we describe them statistically according to the identified street clusters. Moreover, we study the potential impact they may cause in the L_eq evaluation if not discarded.