Validation of calculation method of tunnel portal noise in ASJ RTN-Model 2018 by a field experiment

Abstract

The road traffic noise prediction model ``ASJ RTN-Model 2013,'' which has been developed by the Research Committee in the Acoustical Society of Japan (ASJ), includes an energy-based calculation method of tunnel portal noise. In the method, tunnel portal noise is simply modeled as the sum of direct sound from vehicle sound sources and diffused sound radiated from the tunnel portal. To calculate the diffused sound, point sources are distributed on the portal, and the point sources are assumed to be omnidirectional. ASJ RTN-Model 2018 follows the basic concept of the calculation method, and the diffused sound component has been revised so the point sources have adequate directivities. In this study, such a calculation method was validated by a field experiment using a ``split bamboo type'' tunnel and a test vehicle as a sound source. As a result, it was found that calculation results considerably varied depending on the treatment of the diffused sound component directivity, the positions of the point sources for the diffused sound component, and the diffraction over an oblique tunnel edge, and that the newly introduced calculation setting of the directional sources is the most accurate. The new calculation setting was found to have the advantages of high accuracy and simplicity of calculation.