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-bys results and CPX ones would allow both to infer the road surface influence on the propagation and to evaluate the influence of road surfaces inhomogeneity at roadside. Moreover, the relationship between pass-by results and roadside long-term measures would allow to create accurate power level databases for noise mapping exercise, useful to estimate the noise mitigation reached for all receivers close to the low-noise road surface installation. In this work the results obtained in some measurement sessions, carried out with both CPX method and pass-bys ones, on several different low-noise road surfaces, are used to improve the pass-bys analysis in order to increase the knowledge about the two relationships looked for.