Relationship between Pass By results, CPX ones and roadside long-term measures: Some considerations

The Close Proximity method (CPX) is surely the simpler tool able to evaluate the road surfaces acoustical performances in terms of rolling noise. Anyway, it is necessary to know the noise reduction at roadside for evaluating the true benefit on the noise mitigation given by a low-noise road surface. The methods mainly used to study the road surface acoustical performance at the roadside are the Statistical Pass By and the Controlled Pass By ones. The relationship between pass-by and CPX results would allow evaluating both the road surface influence on the propagation and the influence of road surfaces inhomogeneity at roadside. Moreover, the relationship between pass-by results and roadside long-term measures would allow creating accurate power level databases for noise mapping purposes, leading to a better estimate of the noise exposure for all receivers close to measured road surfaces. Several different low-noise road surfaces are measured, each one multiple times, with both CPX and pass-by techniques. Results are used to improve the pass-by analysis and the knowledge on the two measurement methods' connection.