In Switzerland, the calculation method of road traffic noise is specified in the Ordonnance sur la protection contre le bruit (OPB) (Noise Protection Ordonnance (NPO)). This method is mainly based on observations that were realized in the 80s, and that are not satisfactory many situations anymore. Since the 80s, the traffic volumes have increased, new developments in car and road technologies have occurred, behaviors of users have changed. All these parame-ters contribute to lower reliability of the initial method. Even if the model is still correct in some case such as for fluid traffic, the obtained levels in different types of traffic are hardly reliable. In collaboration with the Swiss Federal Office for the Environment (FOEN), a re-search program has been setup to update the method according to those observations. The ob-jective was to give new guidelines to evaluate emission levels of roads. An important collect of data from cantons and others acoustics partners has been performed as well as measure-ments in real traffic conditions. That made it possible to gather about 7500 points of mea-surement through all Switzerland for several types of road and traffic conditions.