Abstract
This paper describes the major types of noise barrier that have been employed alongside highways, the mechanisms involved in noise reduction and aspects of the research that has been carried out at TRL to improve their acoustic performance. To aid optimisation a mathematical modelling technique using the Boundary Element Method (BEM) has been used to predict the noise reducing properties of a wide range of barriers. Some of the most promising designs have been tested at full scale which has involved the construction of a unique noise barrier test facility (NBTF) at TRL. It was concluded that the average noise screening of simple barriers can be increased significantly by relatively simple modifications. (A)