Acoustic effect of sound absorbing materials and surfaces in road infrastructure

Licentiate thesis, 2024

The most complex road infrastructures are often situated in urban areas which expose hundreds of thousands of people to harmful traffic noise levels. The geometrical complexity and the sound reflecting surfaces of these infrastructures affect the sound propagation, but the noise calculation models, input data and evaluation methods may not be sufficient to correctly predict the noise levels spreading over the neighbourhoods.

The aim of this Licentiate thesis was to investigate the acoustic effect of sound absorbing materials and surfaces in road infrastructure. This was done by changing the absorption indices, α, of existing sound reflecting noise barriers at real sites modelled in the Nord 2000 calculation model. The result showed that absorbers reduced the sound levels, but the effects were site dependent. Furthermore, some results of comparisons between measured and calculated sound levels require further studies, in relation to the question if it is necessary to complement the noise prediction method to be able to prove the acoustic effect of changing materials or installing absorbers.

Since absorption data for direct sound field application (in-situ) were lacking for installed noise barriers and walls, they were obtained by sound Reflection Index, RIQ, measurements using the SOPRA method. This also led to the development of the Direct Field Absorption (DFA) model for evaluating RIQ measurements, which was tested with promising results. The usage of the DFA model, including other applications of it, will be further investigated in the future work, which goal is to propose a methodology for acoustic planning of complex traffic environments.