Measurements on Low Noise Road Surfaces

Low Noise Roads (LNR) are commonly used as an high efficient noise abatement measure direct at the source. A lot of different types of road surfaces, dense and open porous, with full thickness and thin layers, made of asphalt and cement concrete, have been developed. Since the EU-Project SILVIA a systematic classification method for the quantity of noise reduction is under development including different direct measurement methods like Statistical Pass-by Method, SPB (also with Backing Board or with Array technique), Close Proximity Method, CPX, and indirect measurement methods for texture, acoustical absorption and air flow resistivity of the surface. All these methods have advantages and drawbacks and are having systematic and random errors. But there are also principal, physical and non-physical limits of usage. For a special thin layer surface DSH-V5, used on urban roads as well as on motorways, problems with measurements and the estimation of the noise reduction and its acoustical durability will be discussed as an example. The general implementation procedures for correction factors for LNRs in national and international road noise emission models like RLS and CNOSSOS-EU will be remarked.