The assessment of a road “acoustic capacity” methodology and application to a real case of study

In this paper, a new methodology for the definition of the acoustic capacity of a road infrastructure is proposed. The acoustic capacity is rather a new topic as, in the road performance assessment, only the physical capacity is taken into account, or, sometimes, the environmental capacity due to atmospheric pollutants; instead the environmental capacity due to noise, called “acoustic capacity” in the following, is always neglected. For the acoustic capacity assessment, the Harmonoise model has been used: it receives in input traffic data and provides in output noise emission and immission levels which are after compared to the limit levels established by law. Moreover, some problems of implementation on the field of the acoustic capacity methodology are investigated: the position of the receiver in the case of intersections of complex geometry; the noise emission limit values to take into account in case of rush hour traffic. The proposed methodology is applied to a real network: the road network of Piombino, Italy. The results of the application show firstly that the acoustic capacity is actually a constraint involving several traffic flows. Moreover, the acoustic capacity of a road infrastructure is generally lower than its physical capacity, when the noise emission limit value is that imposed by law: that is the acoustic descriptor Lday in our analysis. When the limit value increased by 3 dB(A) for rush hours is taken into account, the acoustic capacity is higher, and is more often greater than the physical capacity.