The Volpe Center Acoustics Facility, in support of the Federal Highway Administration (FHWA) has been conducting a study to investigate the effects of using different ground types based on an improved understanding of the characteristics of the ground types defined in FHWA's Traffic Noise Model (TNM) version 2.5. This study also investigates the effects of using specific pavement types, as opposed to Average pavement, when the pavement type is known. The results of this study indicate that improvements in the correlation between predicted and measured results can be achieved by selecting the best ground type and pavement type for the model.