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1 Supplemental Guidance on the Application of FHWAâs Traffic Noise Model (TNM) The FHWA has provided substantial guidance for the routine application of the Traffic Noise Model (TNM); however, scenarios exist for which there remains limited or no technical guidance. The objectives of NCHRP Project 25-34 were the following: â¢ First, to supplement existing guidance on applying the TNM by identifying best practices to accurately, consistently, and efficiently model (1) structure-reflected noise; (2) bridge expansion joints; (3) signalized interchanges; (4) intersections; (5) area sources, e.g., weigh stations, park-and-ride lots, toll facilities, and service plazas; (6) median barriers; (7) roundabouts; (8) parallel barriers; and (9) tunnel openings. â¢ Second, to determine the sensitivity and accuracy of methods to model (1) multilane highways, (2) rows of buildings, (3) topography, (4) ground zones, and (5) tree zones, and identify best practices for input parameters. These five research topics represent parameters that already exist within the TNM. â¢ Third, to synthesize the state of practice for analyzing the effects of (1) wind direction and (2) temperature on sound propagation. Although considerable data exist on the effects of meteorology on sound propagation, thus far these results have not been applied directly to use within the TNM. NCHRP Report 791 is intended primarily as a guidance document for TNM users and highway noise analysts. As a result, it does not attempt to fully justify or document how the guidance was developed; nor does the report list all of the information, studies, modeling practices, and results that were evaluated to develop the guidance. Instead, those details are included in Appendices A through L of the contractorâs final report, which were prepared to accompany each of the research topic areas and which are available on the NCHRP Project 25-34 web page at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=2986. Sixteen different research topic areas were investigated in detail as part of this study, and significant guidance has been provided on modeling and interpreting results in each of the areas in this report. Even concise summaries of such guidance for each area would require one or more pages of text. Therefore, it is not practical to provide such guidance summaries for each research topic area in this report summary. For summaries of the guidance, the reader is referred to the research topics identified in the chapter titles of this report and to the sections of those chapters describing best modeling practices and guidance. S u m m a r y