A re-analysis of Day-Night Sound Level (DNL) as a function of population density in the United States

This paper focuses on a re-analysis and updating of the 1974 report by the U.S. Environmental Protection Agency entitled: Population Distribution of the United Sates as a Function of Outdoor Noise Level, and commonly known as the 100-site survey. New data, about half of which were gathered throughout the country during 2008 and 2009 and about half of which were gathered in the Baltimore area in about 1998, are presented in this paper, where these different data sets are compared one to one another, and where the total combined data set in terms of the day-night sound level (abbreviated DNL and symbolized L _dn) is examined as a function of population density. The main conclusions are that the original function in the EPA report yields results that are 3 dB higher than results obtained in a free-field situation, primarily because the measurements in that study used a microphone supported on a pole and at a distance of 1.8 m (6ft) from the façade of the building. The new data confirm that the EPA predictions are 3 dB higher than those obtained for a free-field situation. A second main conclusion is that there is neither indication of any significant increase in overall ambient community noise exposure over the past 35 years, nor is there indication of any significant decrease in overall ambient community noise exposure despite 35 years of technological noise control improvements on transportation and other noise sources.