| The main purpose of this research is to make a comparative study of the physical mechanisms related to highway noise barrier insertion loss and to evaluate and improve the accuracy of insertion loss of FHWA Traffic Noise Model (TNM) 2.5 compared with STAMINA 2.0, HNP 1.0 and the field measurement data. As described in Chapter VI, field measurements of highway noise barrier insertion loss were carried out along the I-264. Results show that TNM 2.5 over-predicts the insertion loss for receivers with distances up to 122 m (400 ft). To identify the reasons that TNM 2.5 over-predicts the insertion loss from the perspective of noise diffraction and propagation theories, new software, Highway Noise Predictor (HNP) 1.0, was designed with modified diffraction and propagation theories contained in the TNM Technical Manual and related sources.; The following findings were made based on the research: (i) STAMINA 2.0 and HNP 1.0 predict more accurate insertion loss than TNM 2.5 compared with the measurement data. (ii) TNM 2.5 over-predicts the insertion loss by about 3.0 dBA compared with STAMINA 2.0, from the perspective of diffraction theories. (iii) TNM 2.5 over-predicts the insertion loss by about 2.5 dBA compared to HNP 1.0, from the perspective of diffraction and propagation theories.; Recommendations are proposed to improve the accuracy of predicted insertion loss in TNM 2.5, as described in Chapter IX. Since noise barriers are expensive to build, more accurate prediction of insertion loss by 1.0 dBA, not only means people can be protected by noise barriers with expected satisfaction, but also a significant cost saving potential can be achieved. |
