In situ measurements of the intrinsic characteristics of the acoustic barriers installed along a new high speed railway line a) Massimo Garai a) and Paolo Guidorzi b) (Received: 24 August 2007; Revised: 17 July 2008; Accepted: 18 July 2008) In September 2005 the new high speed railway line Torino-Novara, Italy, was near completion and acoustic barriers had just been installed according to specifications. At this site, the authors conducted in situ verification of the intrinsic characteristics of the noise reducing devices. It is the first European experience of this kind on a large construction workplace. The conditions were extremely demanding and the time scheduled for the task very short. The challenging task was successfully completed applying CEN/TS 1793-5 and taking advantage of the logistic support of the customer.The paper reports the key points of this successful experience and shows some exemplary results.The values measured in situ are compared with the results obtained some years before on products of the same kind. Regarding sound reflection, the in situ method proved to be reliable and to give values more realistic than the laboratory method. Regarding sound insulation, the comparison with previous measurements indicates that, as long as the barriers are well installed, similar results can be expected and that their variance is comparable to that of laboratory tests. On the other hand, large differences (4 – 5 dB or more) indicate poor quality of construction and installation work, that can be confirmed by a careful inspection.This sensitivity of the in situ method to detect faults paves the way to establish minimum construction and installation criteria. It is concluded that the selected method is fully adequate to in situ verification and could be repeatedly applied to check the acoustic durability of noise reducing devices over time. © 2008 Institute of Noise Control Engineering. Primary subject classification: 31.1; Secondary subject classification: 72.9 1 INTRODUCTION The new high speed railway line Torino-Novara, Italy, was opened in February 2006. About 100,000 m 2 of acoustic barriers have been installed along the 86 km of the line to protect the environment from the noise emitted by high speed trains. There are four main types of noise barriers: metallic cassettes filled with glass wool, timber and metal cassettes filled with glass wool, concrete panels with a porous side and acrylic sheets plus smooth concrete panels (see Fig. 1 and Table 1). All of them are constructed in a similar way: acoustic panels supported by steel beams (HE 160 type) which are clamped to a reinforced concrete sustaining wall. The barrier height ranges from 3 m to 5.5 m. In September 2005 the noise screens were almost all installed and the authors were asked to verify their acoustic intrinsic characteristics in situ 1 : this means the sound absorption (or reflection) and the airborne sound insulation, which in European standards are called intrinsic characteristics because they depend only on the device under test and not on the environment in which it is installed. The intrinsic characteristics are different from the insertion loss, which depends also on the environment and on the relative source, receiver and screen positions. The task was very demanding; in fact, it was requested to carry out the measurements: 1. according to high quality technical standards; 2. on site during the final phase of the construction work; a) A preliminary version of this work was presented at InterNoise06 a) Dipartimento di Ingegneria Energetica, Nucleare e del Controllo Ambientale (DIENCA), Università di Bologna- Viale Risorgimento 2-40136 Bologna ITALY; email: massimo.garai@mail.ing.unibo.it b) Dipartimento di Ingegneria Energetica, Nucleare e del Controllo Ambientale (DIENCA), Università di Bologna- Viale Risorgimento 2-40136 Bologna ITALY; email: paolo.guidorzi@mail.ing.unibo.it. 342 Noise Control Eng. J. 56 (5), Sept-Oct 2008