Supplemental Guidance on the Application of FHWA’s Traffic Noise Model (TNM) (2014) / Chapter Skim
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3 C H A P T E R 2 2.1 Introduction When modeling noise levels at receptors located adjacent to an elevated roadway on a structure (bridge or viaduct) , FHWA TNM is capable of predicting the noise generated by vehi cles traveling on the highway structure, taking into account direct noise paths and diffracted noise influences of any noise blocking features (parapets, noise barriers, etc.)
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4reflecting off of the undersides of structures, was evaluated and tested for several projects. A complete description of this technique can be found in a 2002 paper by Reiter and Bowlby.1 Additional discussion of this technique is contained in Appendix A
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5 Practice #1A was compared to the estimated reflective noise component derived from Best Modeling Practice #1B. Details related to this comparative analysis are contained in Appen dix A
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6For the multistep approach, the research team initially conducted noise measurements directly underneath a span of the I-95 viaduct at Schiller Street in Philadelphia where other highway noise sources do not exist. Three sets of simultaneous measurements were taken underneath the viaduct at three positions: • Site 1: Within 5 ft of the bottom of the deck near an expansion joint.
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7 A detailed discussion of the development of this worksheet- based methodology can be found in Appendix A In testing the appropriateness of this methodology at setback locations related to the following projects, the research team found the practice to yield reasonable results: • I-95 projects in Philadelphia, Pennsylvania: Section AFC (nine sets of measurements at Schiller Street)
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8Detailed information associated with the testing process is included in Appendix A The processes, applications, and limitations associated with Best Modeling Practice #2 are given below.
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9 Input Data: 27kced fo edisrednu ot dnuorg morf ,erutcurts fo thgieH :h A ref : Center point between ground and underside of structure (h/2)
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10 determine this practice's potential to account for structure related noise for such a project. This comparison indicated that these two best modeling practices produced similar val ues for the selected receptors.
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