Agenda - Council - 05/28/2002 - Laserfiche WebLink

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-158,- Mr. Steve Jankowski Mr. Brian Olson April 29, 2002 Page 2 Noise modeling was done using the noise prediction program "MINNOISE", a version of the FHWA "STAMZNA" model adapted by Mn/DOT. This model uses vehicle numbers, speed, class of vehicle, and topographical characteristics of the roadway and receptors being analyzed. SP,_F used the grading plans produced by the developers' architects (these plans are the basis ~br the attached figxlres) to determine the elevations of the receptors within the development. Modeling performed for this analysis assumed a peak hour traff~c volume of 2,500 vehicles, of which 97 percent are automobiles and light trucks, two percent are medium trucks, and one percent heavy trucks. This traffic volume was used as a "worst-case" scenario to approximate daytime peak traffic noise levels along TH 47 after the construction of the development. Posted speed limits were used in the noise model. )unalvzed Noise Mitigation To assess the effectiveness of noise mitigation fbr this development, noise barriers of two heights (6 and 10 feet) were modeled along the eastern boundary of the developments (see attached- figures). For the 2nd Addition analysis, the bander extends along the eastern property boundary with a break at the TH 47/I56th [,ane intersection and stops approximately 600 feet south of 156th Lane. Two locations for noise barriers were modeled for the 3rd Addition: west of TH 47 along the highway right-of-way, and west of the wetland. The modeled barrier represents a solid fence or a berm, or a combination of the two. The height of the studied noise barriers was limited to ten feet due to aesthetic, engineering and cost concerns. The locations of potential noise barriers were limited to within the boundaries of the developments except that a potential barrier was modeled along the highway right of way for the .> Addition. While barriers of ten feet in height are effective in mitigating tire noise (tire/road contact noise dominates traffic noise from cars and light trucks), they are not as effective at reducing truck noise, which is dominated by engine and exhaust noise that originate at heights several feet above the road surface. Results of Noise Analysis The results of the noise analysis are presented [n the following tables. Results are presented as [.to A-weighted decibels (dBA). The Lt0 descriptor indicates that the noise levels represent the noise level that is exceeded for the loudest ten percent of a time period, or the loudest six minutes of an hour. "A" weighting approximates, the way that an average person hears sounds. Wildlife Sanctuary 2nd Addition Noise levels at the 2nd Addition of the Wildlife Sanctuary will exceed state daytime noise standards at the four first row homes by up to four dBA. A six-foot-high barrier would reduce traffic noise by zero to three dBA and provide a noticeable decrease (three dBA) at only two residences. A ten-foot-high barrier would provide .a zero to five dBA reduction and provide a noticeable decrease at only two residences. ! I ! I i I I I I