Knowledge of acoustic aging of road pavements is needed by road administrators when developing policies and strategies for noise abatement. It is important to know how noise-reducing pavements, as well as pavements without such acoustic properties, perform over time. Methods such as the American traffic noise model method or the Nordic NORD2000 method use acoustic aging for accuracy in predicting noise. Noise performance models for road pavements are necessary if noise is to be integrated as an active parameter in pavement management systems. This paper contributes to ongoing international development in the field of acoustic aging by performing a comprehensive analysis of results from four Californian and Danish long-time noise measurement studies on asphalt pavements. There is not much information on which changes in the surface structure cause an increase in noise in the period between when the bitumen film is worn off and when the pavement begins to deteriorate with distresses such as raveling, cracking, and so forth. This study analyzes and compares trends in the development of noise over time. The development of the noise spectra is also analyzed. The increase of noise has normally been analyzed in relation to the age of pavements. The traffic load and an artificial indicator, defined as the change of noise predicted as a combination of actual physical age and traffic load, are investigated.
Between 2003 and 2010, research on the changes in tire–pavement noise generation over time was conducted on 11 textures applied to portland cement concrete. The initial textures included longitudinal tining, burlap drag, and longitudinal broom. Additional texturing was applied to these surfaces in the form of longitudinal grooving of varying depth and spacing and diamond grinding with varying spacer dimensions, as well as a combination of the two. Since their application, these sections have been routinely monitored for tire noise performance with the onboard sound intensity method. As originally measured in June 2003, the range in level between the surfaces was relatively small at 2.7 dB. At 5 years, the range is slightly smaller at 2.3 dB. During the total 71/2 years of the study, the overall noise performance increased at an average rate of about 0.10 dB per year. The study has shown that for different frequency ranges the change in noise level has displayed some variation; the lower-frequency levels have decreased for some pavements with time, while the higher-frequency levels have increased at a rate higher than the overall levels for all pavements. For the higher frequencies, findings suggested that the increased noise was due to polishing of the surfaces. For the lower frequencies, the reduction in noise level was less pronounced with more variability between textures. For the ground surfaces, some evidence was found that indicated that the reduction might be linked to some loss of larger-scale texture as the surfaces were worn down.
A measurement program was completed to determine the vertical distribution of heavy-truck noise sources for pass-by events on an in-service highway for vehicles operating under cruise conditions. In addition to data on heavy trucks, some data were obtained for medium trucks and light-duty vehicles. The measurements were performed with acoustic beam forming, which provided visualization of the sound radiation of passing vehicles as well as means for calculating the vertical distribution of noise source level. The data set includes pass-by events for 125 heavy trucks, 30 medium trucks, and nine light vehicles operating nominally at 55 mph on two asphalt surfaces. The purposes of the research were to compare the source height splits assumed in the FHWA traffic noise model (TNM) to the results of this work, examine the acoustic benefit of sound walls designed to block the line of site of truck exhaust outlets, and obtain a better understanding of truck noise sources. For heavy trucks, the pass-by noise is dominated by tire noise produced by the drive axles, with other secondary sources related to the power train occurring in some cases. Noise from elevated exhaust outlets was not observed except in one or two special cases. For all vehicle types, ground level sources (tire noise) produced the highest noise levels. Furthermore, the vertical source distributions were found to be virtually identical for heavy and medium trucks. For truck and light vehicles, it appeared that the current source height splits assumed in TNM may be biased toward higher upper-source strength.
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