For more than 70 years, measurements regarding the acoustic effectiveness of forests and bands of vegetation have been carried out which prove that depths of vegetation of more than 30 m can occasionally achieve siginficant values of sound damping. However, the damping values given in the literature fluctuate strongly due to different considered physical effects as well as deviating basic conditions. Thus, measured damping values cannot be transfered just like that on defined cases of application. Within present standards and regulations of calculating and predicting the noise impact on the significat poins of immission next to traffic lanes, the influence of forests on the sound propagation is considered either not at all or only in a very simplified way.
On behalf of the Federal Highway Research Institute of Germany (BASt), the Gesellschaft für Akustikforschung Dresden mbH presently carries out an extensive measurement campaign regarding the sound propagation nearby and within narrow bands of forests and vegetation next to federal roads and highways. The measurements of the sound propagation take place at different seasons at eight different forests as well as at two measurement sites showing freefield conditions at defined horizontal distances to the road track and at different heigths above ground. Afterwards, statements shall be derived regarding the acoustic effectiveness of bands of the forests having a depth of vegetation of 25 m to 145 m. Aim of the research project is to determine the noise-protecting potential of forests and vegetation – depending among other things on the forestal composition and the depth of vegetation. On that basis, in particular cases, it shall be possible to consider narrow bands of forests and vegetation within calculations of noise propagation and prediction.