A Society of Automotive Engineers (SAE) Cooperative Research Project has established good correlation between pass-by noise data measured on U.S. test tracks conforming to SAE Sealed (sealed asphalt) and International Standards Organization (ISO) surface specifications. Although the ISO surface has a very specific track composition, it does not reduce the variability of the measurements over an SAE Sealed surface. This paper summarizes the project results and determines that the SAE Sealed surface generally produces slightly louder noise levels than a comparable ISO surface when used for pass-by testing; however, the SAE Sealed surface does not represent a consistent upper boundary for the ISO test data. The data supports the use of either track surface for pass-by procedures and suggests that road texture can influence the tire component of vehicle noise. Although the ISO surface has become the requirement for noise regulations in Europe, development work can be completed on the existing sealed test surfaces.
