Agenda Packet Cc - regular meeting 11/13/1989

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DISTANCE (IN FT.) YEAR 2000 L10 YEAR 2000 L50 SITE HOUSE FROM CR 116 DAYTIME NOISE DAYTIME NOISE RECEPTOR (STATION) NUMBER CENTERLINE LEVEL (dBA) LEVEL dBA 44 488+00 3564 9L 64 5r 45 489+40 61 66* 56 46 490+00 3566-3568 100 63 54 47 490+60 3635 122 62 53 * Exceed 65 dBA. Definitions and Standards: The L10 reading is the sound level which is exceeded 10% of the time during the design hnur. L50 is the level which is exceeded 50% of the time. In this study, the design hour usea is the evening peak traffic hour. At other times during the day noise levels are reduced due to lower traffic volumes. Noise is measured in decibels adjusted to the human ear's sensitivity to different fre- quencies (abbreviated dBA). For residential areas, the Federal Highway Administration (FHWA) uses a standard of 70 dBA for L10 but has none for L50. The Minnesota Pollution Control agency (MPCA) uses a daytime standard of 65 dBA fir L10 and 60 SBA for L50. At none of the above sites will road noise exceed the Federal Highway Administration (FHWA) standard of 70 dBA. None of the sites will be subjected to noise in excess of the MPCA L50 standard of 60 dBA. Three of the sites, however, will experience noise in excess of the MPCA L10 standard of 65 dBA. Site 5 will be 3dBA above, Site 42 will be 2 dBA above, and Site 45 will be 1 dBA above the MPCA standard. It is generally accepted among noise experts, including the MPCA, that while the human ear can detect a sudden change of as little as one dBA, a change of at least three or four dBA is needed to detect a difference over a long perioJ of time. Possible mitigation measures: 1. Alignment change. Unfortunately, any shift in horizontal alignment will merely move the source of the noise (road traffic) closer to other nearby houses. A significant shift in vertical alignment can't be accomplished because of the need to match inplace cross roads and driveways. 2. Earth berms. Six feet of horizontal distance is needed for every foot increase in height for earth berms (assumes 3:1 slopes on both sides). The three sites in question range from 50 feet to 61 feet from the center of the road. Subtracting 30 feet for the road and snow storage area leaves only 20 to 31 feet available for a berm. The maximum height would be under 6 feet which is not high enough to reduce noise below the 65 dBA level. 3. Noise walls. Reduction of noise to the 65 dBA level would require an 8 foot high wall between each site and the road. The walls would need to be 400 or more feet long and be continuous. Openings for driveways would destroy the noise reducing effect of the walls. Conclusions: None of the sites will have noise levels above the 70 dBA FHWA standard. Of the 47 sites along the road, none will exceed the MPCA L50 standard and only 3 will exceed the 65 dBA MPCA L10 standard, none of which will exceed it by more than 3dBA. Noise mitigation measures are not recommended. PB/DW;mak 09/29/89;PBNOISE 3