Estimation of the minimum integration time for determining the equivalent continuous sound level with a given level of uncertainty considering some statistical hypotheses for road traffic

Abstract

In this work a relation is obtained for calculating the minimum time necessary for measuring the hourly equivalent level, with preset uncertainty on the L eq in the case of noise produced by road traffic under different statistical hypotheses for vehicular flow. A simple equivalent level prediction model is used as reference. Some specific relations between acoustic power and vehicle speed are implemented in this model. Through the application of the classic theory of errors, the expression for the uncertainty on the L eq is obtained with reference, in particular, to various vehicle distributions: uniform (rectangular), triangular, normal and Poisson that, according to the available information, can be applied for describing traffic flow. Uncertainties over the distance source/receiver and speed of the vehicles are also taken into consideration in the calculation of uncertainty on L eq . The minimum measurement time is obtained from the expression of the error associated with the L eq , according to the hourly number of vehicles, so that the uncertainty on the L eq stays within a preset value. In this case too, the determination of the minimum time refers to the various previously mentioned hypotheses with respect to vehicle distribution. It is shown that it is possible to obtain a correct description of road traffic noise, within a predetermined uncertainty on the hourly L eq , by measuring over times considerably shorter than an hour.