“Noisy” issues in road acoustics: A white paper

Despite almost a century of studies dealing with traffic noise, researchers and practitioners still face old and new issues when designing a low-noise pavement. Given that, this manuscript aims at focusing on a number of unsolved questions, namely theoretical or technological. 1) Is it viable to balance diverse road-related needs (i.e., noise, expected life, texture levels, and friction)? 2) How much does the pavement material affect its acoustic performance (the remaining factors being constant)? 3) How much reliable is the relationship between road texture and mixture aggregate gradation? Based on the analysis of these issues, it emerges that: 1) optimal pavement design involves complex mix optimization and there are theoretical and practical bases to set up a balanced approach to address the complexity of pavement design; 2) high percentages of crumb rubber could optimise road acoustic response but this latter has a relationship with the tyre/road noise (expressed, for example, in terms of close proximity index) that calls for further investigation; 3) aggregate gradation appears to be a reliable basis to predict surface texture and therefore, under given boundary conditions, tyre/road noise; and 4) further studies and investigations are needed in terms of local calibration of deterioration curves and setting up of a sound method to assess the frequency response of asphalt concretes and to govern on-site noise indicators based on mixture properties.