5.2. SR 08-08-2011 - Laserfiche WebLink

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1~ ' by limiting construction activities to daytime hours in accordance with City ordinances and assuring that construction equipment is properly muffled. ' Traffic-Related Noise Federal and state standards have been developed for maximum sound levels in ' residential and commercial areas. By comparing existing and estimated future sound levels to these standards, areas can be recognized that are in need of possible noise mitigation. The analysis that follows characterizes existing traffic noise levels in the project area, assesses the effect of the project on future noise levels, and analyzes potential ' mitigation measures. The noise analysis consisted of selecting specific receptor sites and modeling existing and future noise levels. Analyzed receptor sites consist of the outdoor areas of residential and commercial properties. ' Background Noise is defined as any unwanted sound. Sound travels in a wave motion and ' produces a sound pressure level. This sound pressure level is commonly measured in decibels. Decibels represent the logarithmic measure of sound energy relative to a reference energy level. A sound increase of three dBA is barely perceptible to the human ear, a five dBA increase is clearly noticeable, and a 10 dBA increase is heard twice as loud. For highway traffic noise, an adjustment, or weighting, of the high- and low-pitched sounds is made to approximate the way that an average person hears sounds. The adjusted sound levels are stated in units of "A-weighted decibels" (dBA). In Minnesota, traffic noise levels that are exceeded 10% and 50% of the time during the hour of the day and/or night that has the heaviest traffic. These numbers are identified as the Lio and Lso levels. Table 24-1 provides a rough comparison of the noise levels of some common noise sources. ' Ciry of Elk River Draft Alternative Urban Areawide Review July 2011 Page 75 of 84