THE INFLUENCE OF TYRES ON THE CPX METHOD USED FOR EVALUATING THE EFFICACY OF A NOISE MITIGATION ACTION

The Italian Tuscany Region has decided to adopt the Close Proximity method (CPX) to evaluate the efficacy of using low noise surfaces as mitigation action against the noise pollution. This decision responds to the LEOPOLDO project indications, which aim to provide guidelines establishing criteria on materials and technologies. This set of recommendations is useful for municipalities, allowing them to plan noise mitigation actions based on low-noise road surfaces. However, the public authorities have also to deal with the fact that, within guidelines, it is also prescribed an acoustical performance monitoring for a 3 years period at least. The current release of the draft refers to a future third part of ISO 11819 for all details about the reference tyre to be used. This is necessary because the previous ISO release was considering just dimensions, kind of tread pattern and maintenance conditions as assessment parameters for the tyres. Several tyres available in the market comply with all the requirements, nevertheless choosing a brand rather than another one could influence results of practical verifications, considering that tyre dimensions and tread patterns are the main sources of variability for rolling noise. In this work are presented the results related to the influence of tyre choice for assessing the acoustical performance of a low-noise road surface. This was done comparing results obtained across several measurement sessions, which were repeated using different tyres. A discussion regarding the importance of verifying the noise mitigation action efficacy and about the most appropriate way to carry it out completes this paper.