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Apri I 2009 Noise Analysis TH 36 and Rice Street Interchange Prepared for Ramsey County, Minnesota 1.0 Project Scope and Description SEH has conducted a detailed noise analysis and prepared a noise mitigation plan to address e�sting and future traffic levels associated with the TH36 and Rice St. modification project in Ramsey County, MN. 2.0 Noise Descriptions 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 (dBA) represent the logarithmic increase in 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 ten dBA increase is heard as twice as loud. For example, if the sound energy is doubled (e.g., the amount of traffic doubles), there is a three dBA increase in noise, which is just barely noticeable to most people. On the other hand, if traffic increases to where there is ten times the sound energy level over a reference level, then there is a ten dBA increase and it is heard as twice as loud. For highway traffic noise, an adjustment, or weighting, of the high- and low-pitched sounds, is made to appro�mate 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 impacts are evaluated by measuring and/or modeling the traffic noise levels that are exceeded ten percent and 50 percent of the time during the hour of the day and/or night that has the heaviest traffic. These numbers are identified as the L�o and Lso levels. The L�o value is compared to FHWA noise abatement criteria. RAMSP 105803 Page 1