News and needs in outdoor noise prediction

“Empirical” models for predicting outdoor noise are being replaced by new models based on “physics” and with a wider field of application. This trend is supported by the increasing availability and speed of computers. The future will probably show a move towards numerical methods as a consequence of further increasing computer power. Attempts are being made to separate source and propagation in order to allow independent updating of source models and of propagation models. 1. Background Prediction methods for environmental noise from roads, rail and air traffic and from industry have existed for decades. A recent survey made on behalf of the EU Commission by its Noise Policy Working Group No. 3 on Computation and Measurement concluded that none of the existing methods applied in the EU member states are completely adequate for future use as a common European standard. There is scope for significant improvement, even for the most advanced methods presently available. The day, evening, night noise level LDEN averaged over a reference year will be used in Europe as a metric for environmental noise impact on people. Therefore in prediction we shall have to deal with the combination of varying source noise emission and varying sound path attenuation. The variation can be caused by daily or seasonal variation in source operation (e.g. traffic intensity) and in weather conditions. To simulate the noise levels occurring during a reference year, new investigations are needed on for example traffic noise source emission during warm and cold, wet and dry road surfaces. Likewise, weather statistics are needed for every location in Europe. The nighttime noise exposure in Europe shall be described by LAeq,night that is one of the components of LDEN and perhaps by supplementary metrics such as LAE (SEL) or LAFmax caused by single events. In case such single event noise metrics are introduced, their definition is crucial to the methods for prediction and measurement.