Accuracy and efficiency analysis of a road traffic noise propagation calculation method based on beam tracing

The development and implementation of a traffic noise propagation calculation method based on beam tracing subordinated to spatial subdivision is presented to simulate noise attenuation in three-dimensional space. In the method, complex scenes constituted by road, different buildings and thin sound barrier and all noise propagation modes including direct, reflected, diffracted and composite are considered. The paper analyses the accuracy and efficiency of the method from the perspectives of subdivision precise of obstacles and road, beam thresholds and re-subdivision of sound barrier areas. The results presented by tendencies chart and formulas indicate that a meticulous subdivision and threshold settings lead to more accurate but less efficient method. Results of experiment and case study show the error to be no more than 0.3dB when the building subdivision precisions (0.5m), road subdivision precision (2m) and thresholds (a length threshold of 500m, three reflections and one diffraction) are set appropriately. Re-subdivision of sound barriers is presented to handle the trade-off between accuracy and efficiency caused by discrepancies in the geometric dimensions. In the case study, re-subdivision mitigates the trade-off between accuracy and efficiency, with almost the same accuracy by spending only approximately 1/10 of the time. A building subdivision precision of 1m, a road subdivision precision of 2m, a 500m beam length, 3-5 reflections and a single diffraction are recommended for the method.