Improving the ISO 11819 standards for better characterization of noise reduction of porous pavements

Abstract

The SPB method (ISO 11819-1) is designed to measure the acoustic properties in semi-free field of road pavements at a specific spot along a road, which in practice may characterize a 15-30 m length of the road lane. The CPX method (ISO 11819-2) is designed to correlate well to the SPB method in characterizing road pavements, while extending the measured road section to an arbitrary distance. It is known that both methods may underestimate the noise reduction of porous pavements compared to dense pavements. A remedy for the SPB method may be to extend it to measure equivalent sound exposure levels (SEL) instead. This will be discussed in the paper. Since the microphone locationsin the CPX method have been selected to give the best correlation between noise reductions measured by the CPX and the SPB methods, the inherent problem of the SPB method exists also in the CPX method. As a remedy for the underestimation of noise reduction when using the CPX method, some users have applied other microphone positions around the reference tires than the two mandatory ones. This paper will analyze this problem and suggest how one can avoid it; essentially by adding a microphone behind the tire.