**1.3 Approaches for determining noise barrier effectiveness**

Determining the effectiveness of noise barriers has attracted the attention of researchers for the past 40 years, and a wide variety of both mathematical and experimental approaches have been developed. Mathematical methods have been widely used to determine the diffraction properties of the barriers. These methods can be based on the boundary element method [19, 20], the finite element method [21, 22], and the finite difference method [23].

Experimental studies have been based on diverse approaches relating to (i) the assessment of perceived annoyance reduction efficiency of noise barriers [24, 25], (ii) the effects of noise barriers on the perception of urban soundscape quality [26], (iii) the measurement of noise attenuation based on scale model experiments [27, 28], and (iv) the measurement of the acoustic properties of full-scale barriers. The latter experiments have been the most reported in the literature, and have addressed the analysis of the effectiveness of barriers based on their various acoustic characteristics:


The methods for *in situ* evaluation of barrier effectiveness are described below, with a particular emphasis on those based on the determination of Insertion Loss.
