The Dutch Centre for Transport and Navigation (DVS) and the Danish Road Directorate, Danish Road Institute (DRI) have established cooperation for the period 2004 to 2007 called the DRI-DWW noise abatement program. The goal is to carry out joint research and development in issues related to the abatement of road traffic noise within the framework of the Dutch Innovative Program on Noise (the IPG programme). This final report summarizes results from several studies on the microstructure of porous asphalt pavements and presents improved analysis methods for investigating pavement performance. These techniques, which use drill cores extracted from the pavement, are CT-scanning and preparation of thin and plane sections. The two different research techniques have been applied for investigating the ravelling of porous asphalt pavements, as well as clogging and the effects of using modified bitumen.