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Prediction of road traffic noise in the vicinity of a road tunnel entrance has been one of the most difficult problems. The built-up noise in the tunnel radiates towards outside the entrance. A practical calculation model for this noise radiation is developed in this paper, which is based upon a sound energy balance inside the tunnel. Two imaginary sources are assumed. One is a point source which represents a direct sound from a vehicle in the tunnel. The geometrical location of the imaginary point source is determined by the position of the vehicle and by a new parameter "a" that is related to the acoustical properties of the inside walls. The second is a surface source which represents residual sound with multiple reflection between the walls of the tunnel. This source is specified at the tunnel entrance. Results of a sound level (LAeq) measurement at a highway tunnel shows good agreement with an accuracy of less than 3dB between the calculated and the measured. It is shown that this model is applicable to road traffic noise simulation at a tunnel with a noise control design by absorptive treatment on the walls.
社団法人日本騒音制御工学会の論文