**2.4 Noise barriers transmission loss (***TL***)**

Typical values of the noise barriers transmission loss (TL) parameter when looking at the A-weighted characteristic are from 10 dBA to 15 dBA. Noise barriers should be constructed of materials with a minimum density of 20 kg m<sup>2</sup> . A density of 20 kg/m2 can be achieved by lighter and thicker or heavier and thinner materials (i.e. higher material density enables a thinner material). **Table 1** gives the approximate TL values for some common materials, tested for a typical A-weighted highway traffic frequency spectrum [16]. These values can be used as a rough guideline in designing noise barriers. For more accurate values, one would need to find material testing reports from authorised laboratories.
