This update to the validation of the Federal Highway Administration’s Traffic Noise Model (TNM) provides an evaluation of the performance of TNM Version 2.5 (TNM v2.5) for previously evaluated sites [Rochat 2002] [Rochat 2004] using specific pavement types and updated ground types in the TNM site models. This section reviews the objectives of the TNM Validation Study and reviews some of the findings which motivate the current report. Section 2 discusses the parameters controlled for this study. Section 3 presents results for site models using specific pavements. Section 4 presents results for site models using specific pavements and updated ground types. Section 5 includes a detailed analysis and discussion of the results.
The Volpe Center Acoustics Facility (VCAF), in support of the Federal Highway Administration (FHWA), has been conducting a study to quantify and assess the accuracy of FHWA’s Traffic Noise Model® (TNM) and make recommendations on its use. The TNM Validation Study involves highway noise data collection and TNM modeling for the purpose of data comparison. In previous validation work, sites were chosen in order to quantify the performance of TNM under various real world conditions. Sites included open or shielded areas next to highways with acoustically soft or acoustically hard ground. Over 100 hours of measured data were compared with TNM predicted results using Average pavement for roadways [Rochat 2002].
Although the results of the 2004 addendum showed that TNM v2.5 was performing well, it was concluded that site biases could still be a factor in the outcome of predictions. It was further suggested that pavement type could affect the sound levels [Rochat 2004]. The results from the 2004 addendum also showed that over long distances ground effects were more extreme than expected, namely that acoustically soft ground types were providing too much absorption and acoustically hard ground types were providing too much reflection. Understanding of the best effective flow resistivity (EFR) for various ground types has been refined over the past decade. Based on this new understanding, ground types other than those used in the original modeling may be more appropriate.
This report evaluates the performance of TNM v2.5 when using specific pavements in order to understand how the use of specific pavements affects TNM’s performance. This report also evaluates the performance of TNM v2.5 when using updated ground types for several sites to represent the actual ground types better.
