Special issue on road traffic noise prediction methods

For the past 40 years or more, road traffic noise has been a serious concern in not only Japan but also all countries with a motorized society. Because of the recent increase in traffic on streets and highways, road traffic noise has become a worldwide problem that acoustical engineers should make an effort to alleviate to realize a quieter environment. In an approach to control noise, it is important to develop a scientific method for the calculation of road traffic noise. Much research has been carried out continuously since 1970. As a result of such activities, a noise prediction model for L10 was developed in Britain and published in 1975. As far as I know, it was the first official prediction model that was adopted in a noise policy of a country. This model is called ‘‘Calculation of Road Traffic Noise,’’ and is issued from the Department of the Environment Welsh Office. This noise calculation model was used for noise assessment under the British law, ‘‘The Noise Insulation Regulation.’’ Thirteen years later, in 1988, this method was improved and revised for wide application. In the United States, the Federal Highway Administration (FHWA) published ‘‘Highway Traffic Noise Prediction Model’’ in 1978, which is used to calculate LAeq in the vicinity of highways. A procedure for converting LAeq into Ldn and L10 was provided in this model for the purpose of noise assessment by national or local governments. Software for the model was programmed and made open to the public. Just after the above movements, Scandinavian countries published a road traffic noise prediction method in 1979, and then Germany and France released their models in 1990 and 1997, respectively. The feature of the abovementioned calculation models is that they were developed with different backgrounds, such as noise index, mathematical model (point source or line source), and types of roads, vehicles, terrain, houses and so on. The most important feature is that they are adopted in the noise control policy in each country. In 2002, the European Noise Directive (Directive 2002/49/EC) was officially announced for the purpose of strengthening the noise policy of the European Union (EU). The Member States must adopt and implement the EU Directive. Since the Directive requests a comprehensive policy on environmental noise, working groups were organized to harmonize the existing noise prediction methods in the Member States. The final method, called the ‘‘Harmonoise Model,’’ was established in 2004. The noise calculation model is to be used for preparing strategic noise maps (Lden) in order to develop action plans for major cities in the EU. In Japan, the Acoustical Society of Japan (ASJ) published the first version of a road traffic noise prediction method in 1975 (ASJ Model 1975). It was widely applied in the assessment of noise in the vicinity of roads. Since the revision of the Environmental Quality Standards for noise in 1999, where LAeq was adopted in place of L50 as a noise index, the prediction model has been repeatedly revised every 5 years to comply with the change in Japanese policy on environmental noise. In April 2009, a new version, ASJ RTN-Model 2008, was published in the Journal of ASJ (in Japanese). In developing the model, surveillance studies were carried out and newly obtained knowledge was taken into account. The model is expected to be used in environmental impact assessment, and regular noise monitoring of existing roads through the making of noise maps. In this special issue, the English version of ASJ RTNModel 2008 translated from the Japanese version, is released. Original papers and technical reports related to recent research on road traffic noise are also included in this issue. Some of them are major references to the new model. I hope this special issue will be helpful to all acoustical engineers who are involved in noise control in the sound environment.