Roughness on Dutch railway wheels and rails

Surface roughness on 150 railway wheels and on the rails of 30 sites in the Netherlands have been measured. Block braked wheels were found to show higher roughnesses than the rail at any site. The smoothest rail is 8 dB smoother than the smoothest wheel. It was concluded that in reducing railway rolling noise NS must start to find ways to lower wheel roughness. Only after block brakes have been either removed or optimized will the rail require any attention. An exception to this rule is rail corrugation, which was found to occur locally. A good correlation was found between wheel and rail roughness levels and pass-by sound levels. Also, it was shown experimentally that wheel and rail roughness levels contribute with equal weight to noise production.