Noise Barrier Acoustical Parameters -- Experimental Results

This study attempted to determine those factors which would help improve existing noise barrier prediction models such as included in FHWA's "Noise barrier design handbook" and NCHRP Report 74, "Highway Noise--A design guide for prediction and control." Three specific aspects of the models were investigated: (1) the effects of ground absorption; (2) the relative effects of different cross- sectional shapes, and (3) the barrier surface absorption properties Laboratory Tests (summarized in this digest) were conducted to validate the theoretical findings of the first phase of this study reported in Research Results Digest 105. It is noted that the main area for improvement in current manuals is in the manner of dealing with terrain attenuation, both with and without barrier present. Insertion loss predictions and aspects of ground reflection phenomena are also discussed. Differences in barrier cross-sectional geometry do not significantly affect performance of common barrier configurations beyond the effects already accounted for in the models. Absorptive surfaces on barriers slightly improve barrier effectiveness. Absorptive coverings of highway barriers are treated fairly thoroughly in the final report of this project.