# Statistical Pass-By for Unattended Road Traffic Noise Measurement in an Urban Environment
## 1 Introduction  
The \"Noise in Europe 2020\" report [1] by the European Environment Agency confirmed that road traffic is the most dominant source of environmental noise, with an estimated 113 million Europeans affected by noise levels greater than 55 dB(A) of L\({}_{\text{den}}\) (day-evening-night level). Moreover, at least 20% of the EU population lives in areas where road traffic noise levels are high, and it is likely that the inhabitants underestimate the well-known long-term effect on health that prolonged exposure can produce. Among the many different mitigation actions that can be applied, the laying of new low-noise pavement (LNP) [2; 3], such as open-graded pavement, rubber asphalts or poroelastic surfaces, has become popular as it significantly affects a wider area and a greater number of citizens compared to other actions focused on a single building. LNP is defined as a road surface which can reduce sound emissions to some extent compared to a reference pavement. The most widely used definition of LNP is \"pavement able to provide a reduction of 3 dB(A) with respect to a Dense Asphalt Concrete (DAC)\" [4]. Noise barriers have visible impact that reduces their acceptability [5; 6], and the installation of soundproof windows is much more expensive in cases where there are multiplereceivers to mitigate [6; 7]. Moreover, new windows do not completely solve the problem as citizens leave them open in summertime [8]. The laying of LNP is now a common mitigation action in the EU, and a few methods have been established by technical norms that have emerged over the years in order to evaluate the performances of road surfaces. Among these, the Close Proximity Index (CPX), according to ISO 11819-2:2017 [9], the Statistical Pass-By (SPB-ISO), according to ISO/DIS 11819-1 [10], and the ISO 13472-1:2022 [11], are all non-intrusive methods requiring on-site measurements, unlike ISO 10534-1:1996 [12], which applies in-lab Kundt tube tests to asphalt samples. However, different studies in the past demonstrated that these standard monitoring techniques are not sufficient to reliably evaluate the pavement acoustic efficacy or to directly compare the properties of different ones [13; 14]. CPX has been applied and improved over the years, reaching the status of a well-recognized methodology [15; 16; 17; 18], and its indicators are mentioned within the minimum environmental levels given by the EU Green Public Procurement Criteria (GPP), which were finally defined in 2016 for Europe [19]. The quality of new LNP should then be guaranteed by a mandatory evaluation of its noise emission through CPX measurements, as it is the method that is more directly focused on evaluating the source emission by measuring noise with microphones next to the reference tire of a lab-moving vehicle. On the contrary, SPB-ISO is the right method to identify the sound emitted by real flow or for different vehicle categories, as it is based on noise and traffic data measurements performed at the roadside and at a standard distance. It provides an indicator of noise perceived for a single vehicle and may help to verify the noise efficacy of the pavement or to introduce policies for specific category restrictions or speed limits in contrast to methodologies which acquire the overall noise. Moreover, SPB-ISO is also very helpful for the definition of noise models in the noise mapping and action plan phases. This method is also able to characterize new categories, such as, for example, electric vehicles, which are an emerging issue the definition of which is left open even in the noise mapping official method CNOSSOS-EU [20]. In particular, a variation of the SPB-ISO, the Controlled Pass-By (CPB) [21] is being used in the ongoing LIFE Project E-VIA, aiming to assess the noisiness of electric vehicles on specific-noise pavements [22]. In fact, low-noise pavements can reduce rolling noise; thus, their effect is maximal for electric vehicles [23], whilst it is reduced for heavy vehicles and mopeds.