Determination of the exterior noise environment by statistical assessment of traffic time history patterns

Road traffic noise assessments require the consideration of noise indicators to accurately and reliably assess the prevailing exterior acoustic environment. At a minimum, these will include average noise indicators like equivalent sound level (Leq) and single event noise indicators like maximum sound level (Lmax). However, there is an absence of clear guidance in the United States of America (USA) as to how these indicators should be defined and measured so there is a clear link between the accuracy of the measurements and reliability of the data as presented. This paper offers a measurement strategy, specific to road traffic noise, capable of yielding statistically reliable estimates for Leq and Lmax. The proposed strategy is based upon statistical analyses of time history noise levels, recorded at various sites across Connecticut and California, in order to establish minimum reliable sampling times for each type of indicator. The study draws conclusions on appropriate estimates for Lmax based on a defined measurement period, as well as how reliable the Leq level over this time period is representative of a longer term level. Finally, an initial similarity study of diurnal profiles in USA and European cities is performed, providing a baseline assessment indicating whether data can be applied in general context throughout developed nations.