# Statistical Pass-By for Unattended Road Traffic Noise Measurement in an Urban Environment
## 1 Introduction
Low-noise surfaces were also recently under study in a combined solution with Intelligent Transportation Systems (ITS) in order to maximize their mitigation effect with more focused traffic [24]. Even though both CPX and SPB-ISO are widely performed around the world [25; 26; 27], they have been shown to not fit perfectly into the urban environment, especially the standard SPB methodology [13]. In addition, the SILENCE project contributed to the development of the Backing Board variant (ISO 11819-4 [28]), the measurement of which is still influenced by the real world in front of the microphone. SPB-ISO measurements not only require a free field around the mics, which is rare in an urban context, but also single vehicles passing within a sufficient time spacing. Such a condition almost never happens on urban roads during the daytime, especially on the major and most impactful roads that have high traffic flow. Traffic lights, pedestrian crossing and roundabouts are also urban issues that group vehicles together, especially during daytime, which is the period when attended SPB-ISO should be carried out. Thus, a method able to determine vehicle noise on road pavements in any urban context was still being looked for when the LIFE NREiDE [29] project was conceived. The project, among others, also aims to develop innovative measurement protocols and new methods to verify the efficacy of low-impact surfaces to improve soundproofing performances and reduce annoyance in the urban context, such as through the use of P-U sensors [30]. Therefore, the NREiDE project intends to improve the existing measurement protocol of SPB in order to provide institutions with more reliable data from monitoring campaigns. The present work presents a methodology to determine average noise levels emitted by vehicles categories in an urban context. The outcome is called Urban Pass-By (U-SPB) and mixes standard long-term noise measurement with the SPB-ISO method. It has the advantages of an easy setup of common instrumentation, and, most importantly, it can be unattended during the data acquisition, thus, sparing man hours. The developed algorithms allow the elaboration of the measurements to obtain a U-SPB index that is comparable with the SPBI set by ISO/DIS 11819-1. Finally, the most important advantage is that this procedure implements statistical pass-by in an urban context, ascribing value to such results for mitigation purposes. The present paper details the measurement setup and the analysis procedure of U-SPB. The testing and validation phases are based on specific measurement campaigns performed in Tuscany, Italy, and application to monitor the noise performances of new surfaces in an urban context is also shown. The locally estimated values are not generalizable for all road surfaces, making the U-SPB a method that is not developed enough to label road surfaces over their entire stretch as the CPX does. However, this behavior turned out to be a pro in different contexts, such as the local evaluation of a road noise mitigation action or the evaluation of the effectiveness of traffic reduction measures (times of prohibition of freight transport, bus lines, electric vehicle policies, speed limits, etc.) on the noise impact. This aspect represents an added value for policy makers and allows the correct planning of traffic route policies such as freight-banning times, bus routes, electric vehicle policies, speed limits, etc. The procedure also allows the estimation of long-term Lden according to a relation based on measured road traffic flows only. This allows the avoidance of spurious events or unwanted noise sources in the evaluation of people exposed to the noise specifically emitted by the investigated road.