Spectro-temporal analysis of road traffic noise in the Rome and Milan pilot areas of the DYNAMAP project

The continuous increase of population living in urban areas has worsen the problem of traffic noise, becoming a serious health hazard for citizens. In this context, and following the European Noise Directive 2002/49/EC drawn up for this purpose, the LIFE+ DYNAMAP project has developed a dynamic noise mapping system to represent the acoustic impact of road infrastructures in real time through Wireless Acoustic Sensor Networks (WASNs) deployed in a urban (Milan) and suburban (Rome) pilot areas. For this purpose, an Anomalous Noise Event Detector (ANED) has been implemented to discard all environmental sounds unrelated to road traffic during the traffic noise mapping generation. To train the ANED properly, several investigations have been focused on the analysis and characterization of anomalous events. However, the performance of the algorithm can be also affected by the characteristics of road traffic noise (RTN), which is the main source in both acoustic urban and suburban environments. This work focuses on the analysis of the spectro-temporal distribution of the raw acoustic data collected in both pilot areas by means of a WASN through two representative locations from each pilot area during a weekday and a weekend day, paying special attention to the low frequency range as it contains the main frequency energy components of RTN. The study also takes into account the locations of the sensor nodes, as well as the differences between day and night. One of the most relevant conclusions is that the spectro-temporal distribution of the signals is highly dependant of the environment, presenting higher frequency distribution in the case of the suburban area of Rome - due to a probable higher speed of the vehicle traffic -, and lower in the Milan urban environment.