Analysis of efficiency and usefulness of top devices in noise barriers

The aim of the MAITE project "Transport infrastructure noise attenuation: design and system modelling of additional devices" was to design and evaluate the effectiveness of a new top device designed by TECNALIA. On the first step of the project it was carried out a comparison of the acoustic effect of different geometries using 2D Boundary Element method. Afterwards, the most effective design was evaluated according to the European specifications CEN/TS 1793-4. Those results were presented in INTERNOISE 2010. This paper presents results of insertion loss obtained by the "in situ" evaluation, based on the direct approach of ISO 10847:1997. The evaluation was carried out in a main road (BI-631) with the collaboration of the Provincial Government of Bizkaia, who facilitated the installation of a noise reducing device on top of an already installed noise barrier. It was proved that the top device reduces noise levels at some extent. Additionally, the paper analyses the usefulness of installing top devices. Therefore it identifies the situations where their installation could be interesting and it shows some practical examples to underline possible benefits achieved by using them. The intention is to open a discussion about the practical suitability of installing a top device.