The permissible sound level of road vehicles is part of the EU vehicle type approval legislation, as laid down in EU Directive 70/157/EEC [1] and in the UN-ECE Regulation No 51 [2] , which specifies the test method for the noise emission test. Since 1984 several studies [48] [49] [50] [51] [52] showed that the test method, that had been in force with amendments since 1970, did no longer reflect the real life driving behaviour in urban traffic. In particular the contribution of tyre rolling noise to the total noise emission was underestimated in the test method. This fact was stated in official documents (e.g. the Green paper concerning the Future Noise Policy – 1996 [39]) and the development of a revised test method started in ISO TC43 WG 42 “Measurement of noise emission (external) from road vehicles”. This resulted in 2007 in a new version of the standard ISO 362 [4]. The UN-ECE GRB (Groupe Rapporteur Bruit = Working Party on Noise) has published a new test method in 2007 based on the revised ISO standard with the purpose to monitor the application of this new method in parallel with the existing test method and to evaluate the qualities of the new method. During a period of three years the new method has been used for monitoring purposes. The monitoring period under UN-ECE Regulation No 51 lasted from 1 July 2007 until 1 July 2009, while the monitoring period under Directive 2007/34/EC [3] started on 6 July 2008 and expired on 6 July 2010. During the monitoring periods the results of the current and of the new test method were submitted to the European Commission. By this procedure a database of parallel test results has been collected that offers a good opportunity to investigate the qualities of the new method and to quantify the differences between the results of the two methods. At the request of the European Commission, DG Enterprise and Industry, Unit Automotive Industry, TNO has executed a study into the differences between the current type approval test method A and the proposed new test method B. The goal of the study was to “assess the available noise data in relation to the draft new test protocol and to provide possible new limit values for each category of vehicles, as well as for the derogations currently granted for certain types of vehicles.”