Some Aspects of Characterizing Vehicle Noise Using Single Event and Maximum Pass-by Level

In the NCHRP Project 25-45, pass-by measurements were conducted on 1,289 heavy trucks, 83 medium trucks, and 101 automobiles at 20 different sites in California and North Carolina. Initially, these data were used for the purposes of noise source localization; however, recently, this has been expanded to include more conventional pass-by measurements in order to assess the use of sound exposure level (SEL) in comparison to maximum pass-by level (Pmax). The relationship of these metrics varied with a range in slope of 0.57 to 0.94 and coefficients of determination of 0.55 to 0.91. The sites also provided a range of topographical and terrain conditions between the 25- and 50-foot microphone measurement locations with some being flat, recessed, or elevated to the roadway and to each other. They also included a variety of pavements with 13 asphalt pavements of varied aggregate sizes and seven of Portland cement concrete (PCC) with different texturing. The sites also included uphill, downhill, and level highway grades. Pass-by time histories were also evaluated to assess differences in site characteristics due to these conditions.