Effects of Temperature Induced Inversion Conditions on Suburban Highway Noise Levels

Noise levels were measured near a major highway in the suburban region near Phoenix, Arizona, USA during a two week period in March, 2004 to identify the reasons for increased noise levels during early morning hours. The noise levels were accompanied by meteorological measurements as well as traffic counts to fully describe the problem. The noise levels were measured in one-third octave bands at locations between 100 ft. to 2620 ft. (30–800 m) from the highway and included data on both sides of the highway to discriminate symmetric temperature effects from asymmetric wind effects. The meteorological data indicated inversion conditions or downward refraction during the times of interest and model results from a Parabolic Equation (PE) calculation indicated good agreement with the data. The field data indicated levels of approximately 50 dBA in the neighborhood under neutral conditions. The data and model indicated an approximately 10–15 dB increase in these levels during early morning inversion conditions, which rapidly transitioned to neutral and lapse conditions shortly after sunrise. The results further indicate that for this site and these measurements, temperature effects were the dominant feature increasing noise levels, while wind effects acted to locally increase or decrease levels about the elevated mean. The results of the modeling effort, as well as the data, are presented and discussed. (Work supported by the State of Arizona Department of Transportation)