Determination of traffic noise barrier effectiveness.

This study evaluated the benefits of a noise control program involving construction of over $13 million of traffic noise barriers along Interstate 440 in Nashville, TN. In addition, much of I-440 was depressed in a rock cut with an objective of reducing the traffic noise levels. There were four basic objectives to the study: (1) determine barrier insertion losses at various sites for various geometric configurations; (2) determine change in community noise levels (from before the highway project); (3) study effectiveness of sound-absorbing blocks used on one section to minimize multiple reflections between parallel barriers; and (4) investigate reasons for any differences between predicted and measured insertion losses. Measurements of A-weighted average sound levels and noise reduction were made at over 40 sites. Calibrated predictions of levels without the barriers were also made. Differences in design geometries, terrain, and construction techniques made it impossible to generalize results from one measurement area to the next. The study also afforded the opportunity for a major application and evaluation of the indirect measured and indirect predicted methods in ANSI S12.8-1987, ‘‘American National Standard Methods for Determination of Insertion Loss of Outdoor Noise Barriers.’’