CCP 01-11-1999 - Laserfiche WebLink

Home Browse Search

. I , I I I I I I Ie I I I t I I I Ie "'2'hJ period and the location of the receiver relative to the sound source, Because of the wide range of energy in sounds, sound is typical]y measured using a logarithmic unit called the decibel (dB). Noise levels are typical]y reported in "A" weighted decibels (dBA) to reflect the fact that the human ear is not as sensitive to low frequency sounds as it is to middle and high frequencies. The existing environment in the vicinity of the proposed project is subject to noise from motor vehicles, Traffic noise leve]s vary significantly over time. Traffic noise is dependent on traffic volumes, vehicle speeds and vehicle types. The primary source of vehicular noise in the study area is traffic on I-35W because of the large volume of traffic on the freeway, the speed of the traffic and the high percentage of trucks in the traffic mix. Some general characteristics of traffic noise are as follows: · Traffic noise increases with increasing traffic volumes, A doubling of the traffic volumes results in a 3 dBA increase in noise levels at adjacent receivers. · Traffic noise decreases with increasing distance from the road, Traffic noise levels diminish by 3 to 4.5 dBA per doubling of distance from. the road depending on the intervening terrain. · While the human ear can detect changes in noise ]evels of I dB for a constant noise source, for a time-varying noise source such as traffic, the smallest noticeable change is 3 dBA. A ]0 dBA change in noise levels is perceived to be a doubling of the loudness of the sound. · Trucks tend to generate substantially more noise than cars. A heavy truck traveling at 45 MPH will generate a noise level of approximately 84 dBA at 50 feet. A car traveling at 45 MPH will generate a noise level of approximately 69 dBA at 50 feet. · Traffic generates more noise at higher speeds. A car traveling 30 MPH generates approximately 62 dBA at 50 feet. A car traveling 50 MPH generates approximately 7] dBA at 50 feet. The State of Minnesota has established noise standards for various land use types. The standards are in terms of the LI 0 noise ]evel which is the sound level exceeded ten percent of the time or six minutes out of an hour and the L50 noise leve] which is the sound level exceeded fifty percent of the time or thirty minutes out of an hour. The state noise standards are shown in the following table. TABLE 5-9 STATE NOISE STANDARDS DA YTIME NIGHTTIME (7:00 AM TO 10:00 PM) (10:00 PM TO 7:00 AM) LAND USE L10 L50 L10 L50 Residential 65 60 55 50 Commercial 70 65 70 65 Industrial 80 75 80 75 Source: Minnesota Rules Parts 7030.0010 to 7030.0080 WISP ARK Rice Creek Corporale Park Draft EIS December 10, 1998 Page 8 I