The Need for Updated Traffic Noise Spectra, Used for Calculation of Sound Insulation of Windows and Facades

The international standard ISO 717-1 is used for defining single-number quantities for airborne sound insulation in buildings and of building elements. It also takes into consideration spectrum adaption. The Ctr-spectrum, which represents urban road traffic, originates from the Nordtest Method NT ACOU 061 (1987). This spectrum is the average of measurements done in Denmark and Sweden in the 80-ies. A closer look at the original reports reveals a difference in the two spectra at low frequencies, and indicates an influence by other low-frequency sources.Given the development in vehicle technology during the last decades, it is reasonable to assume that the Ctr-spectrum in ISO 717-1 is more dominant in the low frequencies than the actual urban road spectrum generated from vehicles today. Recent tests in Italy (2013) also point in this direction.Ctr-correction is used for calculating indoor noise levels from outside traffic noise and for characterizing the performance of building elements. Examples of calculations with typical constructions are presented using both the Ctr-spectrum and a spectrum that is typical for today's urban road traffic. The consequences of uncertainties in existing the Ctr-spectrum and of using an updated traffic noise spectrum are discussed.