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Optimization of Heavy Truck Operating Parameters to Minimize Passby Noise The Sound Exposure Level (SEL) of 88 dB at the reference passby distance of 40 feet cited above represents the mean noise level associated with a variety of truck operating parameters, including variations in truck speed, gear usage, engine RPM, direction, load, and accelerationideceleration. As such, individual passby noise levels ranged from 7 dB below the .. mean to 4 dB above the mean. In an attempt to isolate the heavy truck operating parameters which result in the lowest passby ... noise levels, a subsequent heavy truck passby test was conducted on June 26, 2009 between 11 a.m. and 1 p.m. The test was conducted at four positions along the western boundary of the Munn & Perkins project site at locations set back from the roadway distances of 50, 100, 200, . and 300 feet. The nearest passby noise measurement site corresponds to Site 3 shown on Figure 2, with the other three passby test sites located due south of Site 3 at the distances described above. .. During the test period, only trucks arriving or departing the Munn & Perkins facility were monitored. with the truck drivers reporting their speed, RPM, and gear by radio as they passed .. the noise test locations. Data on truck travel direction and load were also recorded for each passby. Only passby noise level data which was not contaminated by the presence of other vehicles were utilized for this analysis, resulting in 32 acoustically clean heavy truck passby .. noise samples monitored simultaneously at four distances from the roadway. One of the trucks monitored during the supplemental noise survey was a "control" truck, with the .. driver instructed to make passes by the test location using distinct values of speed, rpm, and gear usage. After several passbys of the control truck with the truck empty, the trailer was loaded and the tests were repeated. In addition to the control truck, all other trucks entering or leaving the site during the test period were asked to report their operating parameters without being instructed to operate their truck in a particular fashion. The results of the additional passby tests were analyzed to identify those combinations of speed, rpm, and gear that resulted in the lowest passby noise levels. That analysis resulted in the following conclusions: _ • Truck speeds ranged from 30 to 55 mph during the passby tests, with a mean speed of 40 mph. Truck gear usage ranged from 6'" gear to 9"' gear during the passby tests, with a mean of 71" gear. Truck engine speed ranged from 700 to 1900 rpm during the passby tests, with a mean of 1200 rpm. Environmental Noise Analysis !Nunn &Perkins Expanded Hours of Operations—San Joaquin County Page 27