Improving the insertion loss of traffic noise barrier in urban area

Abstract

Noise barriers are the common acoustic measures which are used to minimize the disturbance of traffic noise to residents, especially in suburban and rural areas, these barriers are an effective measure. In a denser built up environment though, they are less effective. It is essential to have an accurate prediction scheme for barrier designs. Poor prediction schemes will lead to an undesired performance of barriers or waste of money for over design. There are often many conflicting design factors that have to be considered when specifying a barrier. The limited space there leads to small source-barrier and barrier-building distances. The latter gives rise to multiple reflections of sound waves between barrier and building. Especially the noise at lower frequencies, are built up by these reflections and could lead to high sound pressure levels. Having a way to reduce these low frequency levels would be interest for many cases where barrier have been applied. Evaluating barrier performance periodically is an important issue for assuring the efficiency of barrier. The international standards state methods for evaluating the performance of a built barrier. The American National Standards Institute ANSI S12.8-1998 has been applied in field measurement for the highway that acts as equivalent site without noise barrier. The noise level measured exceeded the noise limit set by DOE Malaysia. In this study, the empirical formula from ISO 9613-2 has been used to predict the performance of barrier by using the geometry of existing noise barrier for the residential area on the same highway. Similarly, the same method ANSI S12.8-1998 was used to measure the noise level behind the noise barrier at urban residential area. Some of the data obtained still exceeded the noise limit for residential area in urban area. The difference of sound pressure level between prediction and field measurement was then added to the ISO 9613-2 formula to recommend the improvement of insertion loss in term of barrier geometry and the shape of barrier’s top