Abstract
Noise barriers are installed on highway entrance ramps etc. of roads by overlapping them to control noise leaking from barrier openings. The overlaps should be designed to be as short as possible while providing the required noise blocking capability. This paper proposes the LBE-11 method: a method of calculating the noise levels LA,LB in the vicinity of overlapped noise barriers. LBE-11 considers the fact that noise increases by being transmitted directly, reflected, and diffracted from the opening of the overlap and the fact that noise is greatly dampened as it is transmitted from above the overlapped part of a noise barrier. These modes of transmission are calculated by substituting the transmission of sound through the four openings. And it was confirmed that the LBE-11 method has precision sufficient for practical use by performing an evaluation based on a 1/25 scale model experiment. Furthermore, trial calculations of linear sound sources of traffic noise to study simplification of the calculation to optimize the overlap length had been performed. The results clarified that even if the noise transmitted above the location where the sound barrier is overlapped is considered to be noise transmitted above a single wall, the design of the overlap length is adequate, but reflected noise and diffracted noise at the opening of the overlap must be considered.
