Traffic noise emission is largely influenced by the road surface properties. Thus acoustic monitoring of road surfaces is an important tool for road owners to support their maintenance strategy. A CPX (Close ProXimity) test vehicle for dynamic measurements of rolling noise is currently used in France as an expert method for qualifying new pavements. But recently, the method was adapted to the acoustic survey of large networks. In the first part, the measurement device is briefly described, and the principles of the survey method are presented. A round-robin test showed that the expression of results on 100 m long segments gives an optimal reliability. In the second part, an application of this acoustic survey method is presented on the Nantes ring road, where road authority promoted the progressive resurfacing of pavements by the same type of low noise pavement : a semi-porous very thin layer asphalt concrete. Consequently, the 40 kilometer long ring road is now a patchwork of pavement sections of the same type but of different ages. The acoustic monitoring of the road gives in one run an interesting comparison of acoustic performances of this thin layer technique over time, from new until approximately 9 year old.