TNM sub-source height analysis - TNM-defined heavy truck versus user-defined heavy truck

The use of TNM 2.5 to predict traffic noise levels and design traffic noise abatement in the form of noise barriers is influenced by the sub-source heights for heavy trucks, with sound energy emissions at 0 feet and 12 feet above ground level. Recent field measurement studies indicate that the upper (12-foot) sub-source may be overestimating the height of the sound energy from heavy trucks. Therefore, an alternative modeling methodology is investigated that reduces the height of the upper sub-source for heavy truck sound energy. A user-defined vehicle type that contains the noise energy of a heavy truck but divides the energy between the lower sub-source heights of a medium truck (i.e., 0 and 5 feet) may result in better TNM model validation results and increased insertion loss values for designed noise barriers, particularly for shorter barriers. This paper describes the influence of this modeling methodology on both TNM model validation and barrier analysis results in real-world and hypothetical models.