Laserfiche WebLink
3. Fundamentals of Traffic Noise <br />(e.g., doubling the volume of traffic on a highway) that would result in a 3 dB <br />increase in sound would generally be perceived as barely detectable. <br />3.7. Noise Descriptors <br />Noise in the daily environment fluctuates over time. Some fluctuations are minor, but <br />some are substantial. Some noise levels occur in regular patterns, but others are <br />random. Some noise levels fluctuate rapidly, but others fluctuate slowly. Some noise <br />levels vary widely, but others are relatively constant. Various noise descriptors have <br />been developed to describe time -varying noise levels. The following are the noise <br />descriptors most commonly used in traffic noise analysis: <br />• Equivalent Continuous Sound Level (Leq): Leq represents an average of the <br />sound energy occurring over a specified period of time. In effect, Leq is the <br />steady-state sound level containing the same acoustical energy as the time -varying <br />sound that actually occurs during the same period. The 1-hour A -weighted <br />equivalent continuous sound level (Leq[h]) is the energy average of A -weighted <br />sound levels occurring during a 1-hour period and is the basis for the NAC used <br />by Caltrans and the FHWA. <br />• Percentile -Exceeded Sound Level (Lxx): Lxx represents the sound level exceeded <br />for a given percentage of a specified period of time (e.g., Llo is the sound level <br />exceeded 10 percent of the time and L90 is the sound level exceeded 90 percent of <br />the time). <br />• Maximum Instantaneous Sound Level (Lmax): Lma., is the highest instantaneous <br />sound level measured during a specified period. <br />• Day -Night Level (Ld„): Ld„ is the energy average of A -weighted sound levels <br />occurring over a 24-hour period, with a 10 dB penalty applied to A -weighted <br />sound levels occurring during the nighttime hours between 10:00 p.m. and <br />7:00 a.m. <br />• Community Noise Equivalent Level (CNEL): Similar to L&, CNEL is the <br />energy average of the A -weighted sound levels occurring over a 24-hour period, <br />with a 10 dB penalty applied to A -weighted sound levels occurring during the <br />nighttime hours between 10:00 p.m. and 7:00 a.m., and a 5 dB penalty applied to <br />the A -weighted sound levels occurring during the evening hours between <br />7:00 p.m. and 10:00 p.m. <br />14 Fairview Street Improvements from 9th Street to 16th Street <br />and Bridge Replacement Project Noise Study Report <br />