National Academies Press: OpenBook

Field Evaluation of Reflected Noise from a Single Noise Barrier (2018)

Chapter: Appendix C - Comparison of Phase 1 and Phase 2 Results

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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
×
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix C - Comparison of Phase 1 and Phase 2 Results." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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C-3 C H A P T E R C - 1 Introduction to Appendix C This appendix compares the results of the Phase 1 noise measurements at sound-reflecting barriers with the Phase 2 noise measurements at sound-absorbing barriers. It does not provide background on the subject, overall findings, applications, recommendations, or suggested research. These topics are covered in the main report. The detailed results of the Phase 1 measurements and analysis are available online in Appendix E and in NCHRP Web-Only Document 218: Field Evaluation of Reflected Noise from a Single Noise Barrier— Phase 1 and the detailed results of the Phase 2 measurements and analysis are provided in Appendix B. Site photos for each location are available in Appendix F for the Phase 1 measurements and Appendix G for the Phase 2 measurements. The online files are available for viewing or download from the NCHRP Research Report 886 web page at www.trb.org. The purposes of the measurements and analysis were to investigate the following: If sound levels increased on the opposite side of the road from a sound-reflecting noise barrier due to sound reflections off that barrier. If such an increase was present for a sound-absorbing barrier. If there were other factors that might affect the perception of the sound by a listener in front of the barrier or on the opposite side of the road from the barrier. The comparison of results included differences in the following: Broadband unweighted 5-minute equivalent sound pressure levels—Leq (5 min.)—and 5-minute equivalent A-weighted sound levels. One-third octave band 5-minute equivalent sound pressure levels for equivalent meteorological conditions at Barrier and No Barrier sites. A-weighted L90 (5 min.) and L99 (5 min.) statistical descriptors, compared to Leq (5 min.) at Barrier and No Barrier sites. One-third octave band statistical descriptors, compared to Leq (5 min.) at Barrier and No Barrier sites. Spectrograms several-minute blocks of data and individual pass-by events. In addition, special “difference spectrograms” and “comb filtering” plots were developed and compared.” In this appendix, the unit dB refers to a change in level, both for unweighted sound pressure levels (designated as dBZ per the International Standards Organization and A-weighted sound levels [dBA]). The next chapter summarizes the study locations to reduce the need to refer to the main report or other appendices. The subsequent chapters discuss the results.

C-4 C H A P T E R C - 2 Study Locations Five locations with sound-reflecting barriers were studied in Phase 1, and three locations with sound- absorbing barriers were studied in Phase 2. Table 1 provides details. Because of some issues with locations BA-3 and OH-3, they are not included in the discussion of the Phase 1/Phase 2 comparisons. To assist in understanding the results, the microphone positions at each location are listed in Table 2 through Table 7 and are shown in the cross-sectional sketches in Figure 1 through Figure 6. The I-24 measurements were conducted from 13:13 to 17:20 on August 13, 2014. Most of the 1-minute measurement periods were in an Upwind or Calm wind class. Six sound level analyzers were deployed, three each at the Barrier and No Barrier sites, as shown in Figure 1 and described in Table 2. A concrete median barrier at both the Barrier and No Barrier sites shielded the view of the vehicle tires and automobile engines and exhausts at the 5-ft BarCom03 and NoBarCom05 microphones. It could have also shielded the BarCom03 microphone from some of the reflected noise. Figure 1. Cross-sections at the I-24 Barrier (top) site and No Barrier (bottom) sites. I-24, Murfreesboro, TN (Location BA-1, Sound-reflecting Barrier)

Table 1. Studied locations, Phases 1 and 2. Location Roadway City, State Road Class Lanes Pavement Type Geometry Relative to Adjacent Land Uses AADT (vpd) Percent Trucks Barrier Location Barrier Material Barrier Height at Study Site Phase 1 Sound-reflecting Barriers ATS-3 SR-71 Chino Hills, CA Freeway 6 Portland cement concrete (Longitudinal grooving) At-Grade 60,000 7% ROW Concrete Block atop Berm 13 ft. (7-ft. wall atop 6-ft. berm) BA-1 I-24 Murfreesboro, TN Freeway 8 Dense-graded Asphalt At-Grade 78,140 14% ROW Precast Concrete 16-19 ft. BA-3 Briley Pkwy (SR 155) Nashville, TN Freeway 6 Dense-graded Asphalt Fill (Retaining Wall) 45,820 8% Shoulder Cast-in-Place Concrete 12-13 ft. EA-5 MD Route 5 Hughesville, MD Arterial 4 Dense-graded Asphalt At-Grade 34,160 8% Shoulder Precast Concrete 16 ft. SID-1 I-90 Rockford, IL Freeway 6 Asphalt (Not determined) At-Grade 53,470 9.7% Shoulder Precast Concrete 15 ft. Phase 2 Sound-absorbing Barriers OH-1 I-75 Troy, Ohio Freeway 6 Portland cement concrete At-Grade 63,273 (2015) 21% ROW Concrete with rubber tire chip face 16-18 ft. OH-2 I-70 South Vienna, Ohio Freeway 6 Dense-graded Asphalt Slight cut 45,923 (2015) 30% ROW Concrete with rubber tire chip face 18-20 ft. OH-3 I-270 Grove City, Ohio Freeway 6 Portland cement concrete At-Grade 63,768 (2015) 29% (sampled midnight to 04:00) EOP Concrete / wood fiber face 14-16 ft.

C-6 Table 2. I-24 microphone positions. Mic Name Side of Road Distance from Center of Near Travel lane (ft.) Height above Roadway Plane (ft.) BarRef01 EB 51* 10 (16 ft. above ground, near midpoint of barrier) NoBarRef02 EB 51* 10 (16 ft. above ground) BarCom03 WB 84 5 (9 ft. above ground) BarCom04 WB 84 15 (19 ft. above ground) NoBarCom05 WB 84 5 (9 ft. above ground) NoBarCom06 WB 84 15 (19 ft. above ground) *96 ft. to barrier. I-90, Rockford, IL (Location SID-1, Sound-reflecting Barrier) The I-90 measurements took place on Dec. 26, 2014. Setup started at 07:00 and data collection was done from 13:00 to 17:30. Figure 2 shows cross-sections at the Barrier and No Barrier sites. Figure 2. Cross-sections at the I-90 Barrier (top) and No Barrier (bottom) sites.

C-7 The microphone positions are described in Table 3. Table 3. I-90 microphone positions. Mic Name Side of Road Distance from Center of Near Travel Lane (ft.) Height Above Roadway Plane (ft.) BarRef01 SB 20 20 (5 ft. above barrier) NoBarRef02 SB 20 20 (21 ft. above ground) BarCom03 NB 69 10.4 (6 ft. 11 in. above ground) BarCom04 NB 93 17 (15.5 ft. above ground) NoBarCom05 NB 69 10.4 (5 ft. above ground) NoBarCom06 NB 93 17 (23.5 ft. above ground) SR-71, Chino Hills, CA (Location ATS-3, Sound-reflecting Barrier) On January 28, 2015, data were successfully collected at the SR-71 location from about 9:00 to 13:30, with a 15-minute to 20-minute break in the middle for battery changes. There were calm winds in the morning and some stronger winds toward the end of the sampling. Figure 3 shows cross-sections at the Barrier and No Barrier sites for the SR-71 location, which consisted of six microphone positions, as described in Table 4. Figure 3. Cross-sections at the SR-71 Barrier (top) and No Barrier (bottom) sites.

C-8 Table 4. SR-71 microphone positions. Mic Name Side of Road Distance from Center of Near Travel Lane (ft.) Height Above Roadway Plane (ft.) BarRef01 NB 25 10 (10 ft. above ground) NoBarRef02 NB 25 10 (10 ft. above ground) BarCom03 SB 25 10 (10 ft. above ground) BarCom04 SB 400 ~17 (10 ft. above ground) NoBarCom05 SB 25 10 (10 ft. above ground) NoBarCom06 SB 400 At least 5 ft. (32 ft. above ground)

C-9 MD-5, Hughesville, MD (Location EA-5, Sound-reflecting Barrier) The measurements at the MD-5 location were conducted on June 9, 2015. Two periods were measured. The first period, between 12:00 and 16:10 allowed for higher volume commuting traffic. The second period, between 19:40 and 23:50 allowed for lower traffic volumes and greater sensitivity to individual vehicle pass-bys. Figure 4 shows cross-sections at the Barrier and No Barrier sites. At the MD-5 location, the project team set up six microphone positions, as detailed in Table 5. Figure 4. Cross-sections at the MD-5 Barrier (top) and No Barrier (bottom) sites. Table 5. MD-5 microphone positions. Mic Name Side of Road Distance from Center of Near Travel Lane (ft.) Height Above Roadway Plane (ft.) BarRef01 SB 15 17.5 (5 ft. above barrier) NoBarRef02 SB 18 17.5 (18 ft. above ground) BarCom03 NB 80 5 (9 ft. 3 in. above ground) BarCom04 NB 80 15 (19 ft. 3 in. above ground) NoBarCom05 NB 69 7 (5 ft. above ground) NoBarCom06 NB 69 17 (15 ft. above ground)

C-10 I-75, Troy, OH (Location OH-1, Sound-absorbing Barrier) The measurements at the I-75 location were conducted on Tuesday, November 15, 2016, from approximately 17:00 to 21:00. Figure 5 shows cross-sections at the Barrier and No Barrier sites. The Com microphones were set at 10 ft. and 20 ft. above the roadway elevation to minimize the shielding of the tire noise from northbound vehicles by the concrete median barriers. Table 6 lists the microphone positions. Figure 5. Cross-sections at the I-75 Barrier (top) site and No Barrier (bottom) sites. Table 6. I-75 microphone positions. Mic Name Side of Road Distance from Center of Near Travel Lane (ft.) Height Above Roadway Plane (ft.) BarRef01 NB 25 10 (12 ft. above ground, near midpoint of barrier) NoBarRef02 NB 25 10 (11.5 ft. above ground) BarCom03 SB 50 10 (9 ft. above ground) BarCom04 SB 100 20 (19 ft. above ground) NoBarCom05 SB 50 10 (10 ft. above ground) NoBarCom06 SB 100 20 (19 ft. above ground)

C-11 I-70, Troy, OH (Location OH-2, Sound-absorbing Barrier) Measurements were conducted on Wednesday, November 16, 2016, from approximately 14:30 to 18:30. There was almost no cloud cover, with the temperature dropping swiftly as the sun went down. Winds were calm after sunset. Figure 6 shows cross-sections at the Barrier and No Barrier sites. No concrete median barrier is present at either site. Table 7 lists the microphone positions. Figure 6. Cross-sections at the I-70 Barrier (top) and No Barrier (bottom) sites. Table 7. I-70 microphone positions. Mic Name Side of Road Distance from Center of Near Travel Lane (ft.) Height Above Roadway Plane (ft.) BarRef01 WB 40 11 (11 ft. above ground, near midpoint of barrier) NoBarRef02 WB 40 11 (12 ft. above ground) BarCom03 EB 75 11 (5 ft. above ground) BarCom04 EB 75 16 (10 ft. above ground) NoBarCom05 EB 75 11 (5 ft. above ground) NoBarCom06 EB 75 16 (10 ft. above ground)

C-12 C H A P T E R C - 3 Measured Broadband Level Differences at Reference Microphones Between the Road and the Barrier A Phase 1 finding was that the measured broadband unweighted sound pressure levels and A-weighted sound levels were generally higher at the Barrier microphones than at the No Barrier microphones. This finding held for the reference microphone located midway between the barrier and the road for the I-24 and SR-71 sound-reflecting barriers. Unexpectedly, this finding also held for the reference microphone located midway between the barrier and the road for the I-75 and I-70 sound-absorbing barriers. The results suggest noise is being reflected off these sound-absorbing barriers. Both barriers were made of the same product, which was specified as having a Noise Reduction Coefficient (NRC) of 0.80, meaning the panels were not fully absorptive. However, simple image-source modeling with the Federal Highway Administration (FHWA) Traffic Noise Model (TNM) 2.5 showed that reflections off a barrier with an NRC of 0.80 should have little effect on the total A-weighted sound level at the reference microphone position halfway between the barrier and the road. The results are illustrated in Figure 7 through Figure 10 for I-24, SR-71, I-75, and I-70. Sound-reflecting Barriers Figure 7 shows the differences in the unweighted and A-weighted running Leq (5 min.) for BarRef01 and NoBarRef02 at I-24. For virtually all the running 5-minute Leq periods, the BarRef01 levels, both unweighted and A-weighted, are higher than the NoBarRef02 levels by a range of 0.5 to 1.5 dB. Figure 8 shows the differences for BarRef01 and NoBarRef02 at SR-71. The unweighted levels at BarRef01 are on the order of 0 dB to 1.8 dB higher than the NoBarRef02 levels, averaging approximately 1 dB higher. The A-weighted levels at BarRef01 are on the order of 0 dB to 1 dB higher than NoBarRef02, averaging approximately 0.5 dB.

C-13 Figure 7. Differences in running Leq (5 min.), I-24, BarRef01 minus NoBarRef02. Figure 8. Differences in running Leq (5 min.), SR-71, BarRef01 minus NoBarRef02. Sound-absorbing Barriers Figure 9 shows the differences in the unweighted and A-weighted levels for BarRef01 and NoBarRef02 at the I-75 sound-absorbing barrier location. For virtually all the running 5-minute Leq periods, the unweighted BarRef01 levels are higher than the unweighted NoBarRef02 levels by a range of 0.4 to -0.5 0.0 0.5 1.0 1.5 2.0 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7 D iff er en ce in le ve l, dB Time dBA dBZ -3 -2 -1 0 1 2 3 9: 00 9: 10 9: 20 9: 30 9: 40 9: 50 10 :0 0 10 :1 0 10 :2 0 10 :3 0 10 :4 0 10 :5 0 11 :0 0 11 :1 0 11 :2 0 11 :3 0 11 :4 0 11 :5 0 12 :0 0 12 :1 0 12 :2 0 12 :3 0 12 :4 0 12 :5 0 13 :0 0 13 :1 0 13 :2 0 D iff er en ce in le ve l, dB Time dBA dBZ

C-14 2.6 dB, averaging approximately 1.4 dB higher; the A-weighted levels are higher by a range of 0.2 dB to 1.8 dB, averaging approximately 1.4 dB higher. Figure 9. Differences in running Leq (5 min.), I-75, BarRef01 minus NoBarRef02. Figure 10 shows the differences in levels between BarRef01 and NoBarRef02 for the sound-absorbing barrier at I-70. Over all the running 5-minute Leq periods, the BarRef01 unweighted sound pressure levels range from 0.1 dB lower than those at NoBarRef02 to 1.5 dB higher, averaging approximately 0.7 dB higher. The BarRef01 A-weighted sound levels range from 0.2 dB lower than those at NoBarRef02 to 1.0 dB higher, being approximately one-half decibel higher on average. -3 -2 -1 0 1 2 3 17 :1 2 17 :2 2 17 :3 2 17 :4 2 17 :5 2 18 :0 2 18 :1 2 18 :2 2 18 :3 2 18 :4 2 18 :5 2 19 :0 2 19 :1 2 19 :2 2 19 :3 2 19 :4 2 19 :5 2 20 :0 2 20 :1 2 20 :2 2 20 :3 2 20 :4 2 20 :5 2 21 :0 2 D iff er en ce in le ve l, dB Time dBA dBZ

C-15 Figure 10. Differences in running Leq (5 min.), I-70, BarRef01 minus NoBarRef02. -3 -2 -1 0 1 2 3 14 :3 5 14 :4 5 14 :5 5 15 :0 5 15 :1 5 15 :2 5 15 :3 5 15 :4 5 15 :5 5 16 :0 5 16 :1 5 16 :2 5 16 :3 5 16 :4 5 16 :5 5 17 :0 5 17 :1 5 17 :2 5 17 :3 5 17 :4 5 17 :5 5 18 :0 5 18 :1 5 18 :2 5 D iff er en ce in le ve l, dB Time dBA dBZ

C-16 C H A P T E R C - 4 Measured Broadband Level Differences at the Community Microphones Across the Road from the Barrier The higher levels seen opposite the sound-reflecting barriers were also seen to some extent for the sound- absorbing barriers. At the I-24, MD-5 and I-70 locations, the community microphones were at the same distances from the road, but at different heights above the road. At I-90, SR-71, and I-75, the community microphones were at different distances from the road. Community Microphones at Same Distances and Different Heights I-24, MD-5, and I-70 are discussed here. At all three sites, the community microphones showed higher levels opposite the barrier compared to the No Barrier site. For I-24 (sound-reflecting barrier), Figure 11 shows the differences in the unweighted and A-weighted levels for BarCom03 and NoBarCom05 at the lower height. For most of the running 5-minute Leq periods, the BarCom03 levels, both unweighted and A-weighted, are higher than the NoBarCom05 levels by a range of 0.0 to 1.0 dB, with differences of as much as 1.5 dB. Figure 12 shows the differences for the upper microphones at BarCom04 and NoBarCom06. For most of the running 5-minute Leq periods, the BarCom04 levels, both unweighted and A-weighted, are higher than the NoBarCom06 levels by a range of 0.0 to 0.5 dB, with differences of as much as 1.0 dB. For the other periods, the A-weighted levels at NoBarCom06 are 0 dB to 0.5 dB higher than the BarCom04 levels.

C-17 Figure 11. Differences in running Leq (5 min.), I-24, BarCom03 minus NoBarCom05. Figure 12. Differences in running Leq (5 min.), I-24, BarCom04 minus NoBarCom06. -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7 D iff er en ce in le ve l, dB Time dBA dBZ -1.0 -0.5 0.0 0.5 1.0 1.5 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7 D iff er en ce in le ve l, dB Time dBA dBZ

C-18 For MD-5 (sound-reflecting barrier), Figure 13 shows the differences in the unweighted and A-weighted levels for BarCom03 and NoBarCom05 (lower microphones). For these lower microphones opposite the barrier, the daytime unweighted running Leq (5 min.) at BarCom03 ranged from 1.0 dB lower to 2 dB higher than those at NoBarCom05. The daytime A-weighted levels at BarCom03 generally ranged from 0.5 dB to 2.4 dB higher than those at NoBarCom05. In the evening, the unweighted levels at the two microphones were generally within -2 dB to 1.5 dB of each other. The BarCom03 A-weighted levels ranged mostly from 0 dB to 1.5 dB higher than the NoBarCom05 levels. Figure 14 shows the differences in the unweighted and A-weighted levels for BarCom04 and NoBarCom06 (upper microphones). For most of the running Leq (5 min.) periods during both the afternoon and evening, the BarCom04 levels were higher than the NoBarCom06 levels. The unweighted Leq (5 min.) generally ranged from 0.5 dB lower to 1.5 dB higher during the day and -1 dB lower to 2 dB higher during the evening. The A-weighted levels ranged from 0.5 dB lower to 1 dB higher than NoBarCom06 during both daytime and nighttime. Figure 13. Differences in running Leq (5 min.), MD-5, BarCom03 minus NoBarCom05. -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 12 :0 0 12 :1 8 12 :3 6 12 :5 4 13 :1 2 13 :3 0 13 :4 8 14 :0 6 14 :2 4 14 :4 2 15 :0 0 15 :1 8 15 :3 6 15 :5 4 19 :4 9 20 :0 7 20 :2 5 20 :4 3 21 :0 1 21 :1 9 21 :3 7 21 :5 5 22 :1 3 22 :3 1 22 :4 9 23 :0 7 23 :2 5 23 :4 3 D iff er en ce in le ve l, dB Time dBA dBZ

C-19 Figure 14. Differences in running Leq (5 min.), MD-5, BarCom04 minus NoBarCom06. For the sound-absorbing I-70 location, Figure 15 shows the differences in unweighted and A-weighted levels for the lower microphone pair of BarCom03 and NoBarCom05. For nearly all the running 5-minute Leq periods, the BarCom03 unweighted sound pressure levels range from 0.3 dB to 1.7 dB higher than those at NoBarCom05, averaging approximately 0.7 dB higher. The BarCom03 A-weighted sound levels range from 0.0 dB to 1.2 dB higher than those at NoBarCom05, averaging approximately 0.7 dB higher. Figure 16 shows the differences in unweighted and A-weighted levels for the upper microphone pair of BarCom04 and NoBarCom06. For nearly all the running 5-minute Leq periods, the BarCom04 unweighted sound pressure levels range from 0.5 dB to 2.0 dB higher than those at NoBarCom06, averaging approximately 1.1 dB higher. The A-weighted sound levels at BarCom04 range mostly from 0.5 dB to 1.5 dB higher than those at NoBarCom06 averaging approximately 1.0 dB higher. -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 12 :0 0 12 :1 8 12 :3 6 12 :5 4 13 :1 2 13 :3 0 13 :4 8 14 :0 6 14 :2 4 14 :4 2 15 :0 0 15 :1 8 15 :3 6 15 :5 4 19 :4 9 20 :0 7 20 :2 5 20 :4 3 21 :0 1 21 :1 9 21 :3 7 21 :5 5 22 :1 3 22 :3 1 22 :4 9 23 :0 7 23 :2 5 23 :4 3 D iff er en ce in le ve l, dB Time dBA dBZ

C-20 Figure 15. Differences in running Leq (5 min.), I-70, BarCom03 minus NoBarCom05. Figure 16. Differences in running Leq (5 min.), I-70, BarCom04 minus NoBarCom06. -3 -2 -1 0 1 2 3 14 :3 5 14 :4 5 14 :5 5 15 :0 5 15 :1 5 15 :2 5 15 :3 5 15 :4 5 15 :5 5 16 :0 5 16 :1 5 16 :2 5 16 :3 5 16 :4 5 16 :5 5 17 :0 5 17 :1 5 17 :2 5 17 :3 5 17 :4 5 17 :5 5 18 :0 5 18 :1 5 18 :2 5 D iff er en ce in le ve l, dB Time dBA dBZ -3 -2 -1 0 1 2 3 14 :3 5 14 :4 5 14 :5 5 15 :0 5 15 :1 5 15 :2 5 15 :3 5 15 :4 5 15 :5 5 16 :0 5 16 :1 5 16 :2 5 16 :3 5 16 :4 5 16 :5 5 17 :0 5 17 :1 5 17 :2 5 17 :3 5 17 :4 5 17 :5 5 18 :0 5 18 :1 5 18 :2 5 D iff er en ce in le ve l, dB Time dBA dBZ

C-21 Community Microphones at Different Distances At the two sound-reflecting locations (I-90 and SR-71) and at the sound-absorbing location (I-75), the community microphones showed slightly higher levels opposite the barrier compared to the No Barrier site. At the microphones closest to the road for the sound-reflecting SR-71 barrier, the Barrier/No Barrier differences are small because the microphones are close to the road. At the sound-reflecting I-90 barrier, the Barrier levels at the closer microphones are consistently higher than the No Barrier levels. For the sound-absorbing I-75 barrier, the differences at the closer microphones are more variable, sometimes showing higher levels at the Barrier site and sometimes showing higher levels at the No Barrier site. At the more distant microphones, the Barrier levels were generally higher than the No Barrier levels for the sound- reflecting barriers and, to a lesser extent, slightly higher for the sound-absorbing barrier. Details follow by location. For I-90 (sound-reflecting barrier), Figure 17 shows the differences in the unweighted and A-weighted levels for the microphones closer to the road, BarCom03 and NoBarCom05. For all the running 5-minute Leq periods, the BarCom03 unweighted sound pressure levels are on the order of 0 dB to 1.5 dB higher than the NoBarCom05 levels. For the A-weighted sound levels, the BarCom03 levels are on the order of 0.4 dB to 1.3 dB higher than the NoBarCom05 levels. Figure 18 shows the differences for the more distant BarCom04 and NoBarCom06. For most of the running 5-minute Leq periods, the BarCom04 levels, both unweighted and A-weighted, are higher than the NoBarCom06 levels. The unweighted levels range from 0.7 dB lower than NoBarCom06 to 1.5 dB higher. The A-weighted levels range from 0.2 dB to 1 dB higher. As time passed over the 4-hour period at the I-90 location, the Leq (5 min.) (not shown) dropped slowly, on the order of 1 dB to 2 dB. In this same period the differences in levels between the Barrier and No Barrier microphone pairs increased on the order of one-half decibel. Figure 17. Differences in running Leq (5 min.), I-90, BarCom03 minus NoBarCom05. -3 -2 -1 0 1 2 3 13 :0 0 13 :1 0 13 :2 0 13 :3 0 13 :4 0 13 :5 0 14 :0 0 14 :1 0 14 :2 0 14 :3 0 14 :4 0 14 :5 0 15 :0 0 15 :1 0 15 :2 0 15 :3 0 15 :4 0 15 :5 0 16 :0 0 16 :1 0 16 :2 0 16 :3 0 16 :4 0 16 :5 0 17 :0 0 17 :1 0 17 :2 0 D iff er en ce in le ve l, dB Time dBA dBZ

C-22 Figure 18. Differences in running Leq (5 min.), I-90, BarCom04 minus NoBarCom06. For the sound-reflecting barrier at SR-71, Figure 19 shows the differences for BarCom03 and NoBarCom05. For the microphones adjacent to the shoulder on the opposite side from the barrier, little evidence of reflection is seen because these microphones were so close to the traffic on the lanes opposite the barrier. The unweighted levels at BarCom03 range from 0.9 dB lower to 1 dB higher than those at NoBarCom05. The A-weighted levels at BarCom03 range from 0.7 dB lower to 0.5 dB higher than those at NoBarCom05. Figure 20 shows the differences for the considerably more distant BarCom04 and NoBarCom06. For virtually all the running 5-minute Leq periods, the BarCom04 levels, both unweighted and A-weighted, are higher than the NoBarCom06 levels at these more distant microphones. The unweighted levels ranged mostly from 0 dB to 4 dB higher than NoBarCom06. The A-weighted levels ranged from 1 dB to nearly 4 dB higher. For both unweighted and A-weighted cases, the average difference was 2.1 dB higher at BarCom04. -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 13 :0 0 13 :1 0 13 :2 0 13 :3 0 13 :4 0 13 :5 0 14 :0 0 14 :1 0 14 :2 0 14 :3 0 14 :4 0 14 :5 0 15 :0 0 15 :1 0 15 :2 0 15 :3 0 15 :4 0 15 :5 0 16 :0 0 16 :1 0 16 :2 0 16 :3 0 16 :4 0 16 :5 0 17 :0 0 17 :1 0 17 :2 0 D iff er en ce in le ve l, dB Time dBA dBZ

C-23 Figure 19. Differences in running Leq (5 min.), SR-71, BarCom03 minus NoBarCom05. Figure 20. Differences in running Leq (5 min.), SR-71, BarCom04 minus NoBarCom06. For the sound-absorbing barrier at I-75, Figure 21 shows the differences in the unweighted and A-weighted levels for the microphones closer to the road, BarCom03 and NoBarCom05. At BarCom03, the unweighted levels range from 0.9 dB lower than at NoBarCom05 to 1.5 dB higher, averaging approximately 0.3 dB higher. The A-weighted levels at BarCom03 range from 0.9 dB lower than at NoBarCom05 to 1.4 dB higher, averaging approximately 0.5 dB higher. Figure 22 shows the differences -3 -2 -1 0 1 2 3 9: 00 9: 10 9: 20 9: 30 9: 40 9: 50 10 :0 0 10 :1 0 10 :2 0 10 :3 0 10 :4 0 10 :5 0 11 :0 0 11 :1 0 11 :2 0 11 :3 0 11 :4 0 11 :5 0 12 :0 0 12 :1 0 12 :2 0 12 :3 0 12 :4 0 12 :5 0 13 :0 0 13 :1 0 13 :2 0 D iff er en ce in le ve l, dB Time dBA dBZ -3 -2 -1 0 1 2 3 4 5 6 9: 00 9: 10 9: 20 9: 30 9: 40 9: 50 10 :0 0 10 :1 0 10 :2 0 10 :3 0 10 :4 0 10 :5 0 11 :0 0 11 :1 0 11 :2 0 11 :3 0 11 :4 0 11 :5 0 12 :0 0 12 :1 0 12 :2 0 12 :3 0 12 :4 0 12 :5 0 13 :0 0 13 :1 0 13 :2 0 D iff er en ce in le ve l, dB Time dBA dBZ

C-24 for the more distant BarCom04 and NoBarCom06 positions. At BarCom04, the unweighted levels range from 0.5 dB lower than at NoBarCom06 to 1.9 dB higher, averaging approximately 0.6 dB higher. The A-weighted levels at BarCom04 range mostly from 0.8 dB lower to 1.4 dB higher than at NoBarCom06, averaging approximately 0.5 dB higher. Figure 21. Differences in running Leq (5 min.), I-75, BarCom03 minus NoBarCom05. Figure 22. Differences in running Leq (5 min.), I-75, BarCom04 minus NoBarCom06. -3 -2 -1 0 1 2 3 17 :1 2 17 :2 2 17 :3 2 17 :4 2 17 :5 2 18 :0 2 18 :1 2 18 :2 2 18 :3 2 18 :4 2 18 :5 2 19 :0 2 19 :1 2 19 :2 2 19 :3 2 19 :4 2 19 :5 2 20 :0 2 20 :1 2 20 :2 2 20 :3 2 20 :4 2 20 :5 2 21 :0 2 D iff er en ce in le ve l, dB Time dBA dBZ -3 -2 -1 0 1 2 3 17 :1 2 17 :2 2 17 :3 2 17 :4 2 17 :5 2 18 :0 2 18 :1 2 18 :2 2 18 :3 2 18 :4 2 18 :5 2 19 :0 2 19 :1 2 19 :2 2 19 :3 2 19 :4 2 19 :5 2 20 :0 2 20 :1 2 20 :2 2 20 :3 2 20 :4 2 20 :5 2 21 :0 2 D iff er en ce in le ve l, dB Time dBA dBZ

C-25 C H A P T E R C - 5 One-Third Octave Band Differences for Equivalent Leq (5 min.) Periods In the data analysis for the FHWA Method (comparing one-third octave band levels at Barrier and equivalent No Barrier sites), figures were generated to show differences in level between comparable microphones for an average of all the equivalent data groupings for a particular meteorological class, including error bars representing +/- one standard deviation for each average value. Each figure has three graphs: î BarRef01 minus NoBarRef02 in the upper graph. î BarCom03 minus NoBarCom05 in the middle graph. î BarCom04 minus NoBarCom06 in the lower graph. Each graph shows the averages of the average level differences for the A-weighted sound level, the unweighted sound pressure level and the one-third octave band sound pressure levels from 20 Hz to 10 kHz. As noted in the previous section, at the I-24, MD-5, and I-70, the community microphones were at the same distances from the road, but at different heights above the road. At I-90, SR-71, and I-75, the Com microphones were at different distances from the road. Community Microphones at Same Distances and Different Heights For the sound-reflecting barrier at I-24 (for the Upwind Lapse groups), Figure 23 shows in the upper graph that, in general, the BarRef01 levels are approximately 0.9 dB to 1.3 dB higher than the NoBarRef02 levels across the entire spectrum. Higher levels at BarRef01 are expected since the microphone is between the barrier and the road. At 25 Hz, the difference is 2 dB; at 200 Hz and 250 Hz, it is approximately 0.5 dB. The middle graph of Figure 23 shows the differences in levels between BarCom03 and NoBarCom05, both of which were 5 ft. above the roadway elevation. In general, the BarCom03 levels are equal to or slightly greater than the NoBarCom05 levels over most of the frequency range through 4 kHz. The increase is less than 1 dB from 31.5 Hz to 250 Hz, and on the order of 1 dB to 2 dB in the bands from 315 Hz to 1 kHz. Above 4 kHz, the levels at NoBarCom05 are higher than the levels at BarCom03. The difference was caused by insect sounds in the vegetation behind the NoBarCom05 microphone that were not present near the BarCom03 site. The lower graph of Figure 23 compares the levels at BarCom04 and NoBarCom06, both of which were 15 ft. above the roadway surface. The results show that the BarCom04 levels in the frequency bands from 20 Hz through 1.25 kHz were equal to or slightly higher than at NoBarCom06. At 31.5 Hz to 63 Hz, they were approximately 1 dB higher than NoBarCom06. At 1.6 kHz and above, the NoBarCom06 levels were higher than the BarCom04 levels ranging from a fraction of 1 dB at 1.6 kHz to 2.5 dB in the 6.3 kHz band. The higher levels at NoBarCom06 in the bands are attributed to insect noise in some vegetation behind this microphone.

C-26 Figure 23. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), all microphones, for all Upwind Lapse groups, I-24. -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All ULG Groups -6.0 -4.0 -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All ULG Groups -4.0 -2.0 0.0 2.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All ULG Groups

C-27 For MD-5 (sound-reflecting barrier), Figure 24 shows the results for the Downwind Neutral class. The upper graph shows that, in general, the BarRef01 levels vary little compared to NoBarRef02 from 500 Hz through 6.3 kHz. Below 500 Hz, the BarRef01 levels were generally less than 1 dB above those at NoBarRef02. Little difference is expected because the BarRef01 microphone was atop the barrier, not in front of it like I-24 and I-70. The middle graph compares the levels at BarCom03 and NoBarCom05, the lower-height microphones. Through 125 Hz, any differences are less than 0.5 dB. From 160 Hz through 500 Hz, the BarCom03 levels are higher, ranging from 1 dB at those ends of the range up to 6 dB at 315 Hz, the key band for the Calm Neutral class. From 630 Hz through 6.3 kHz, the BarCom03 level is higher by 0.5 dB to 1.5 dB (at 2 kHz). The barrier reflection effect is prominent in the low-frequency range (250-500 Hz), as was also seen for the same microphones for the I-90 location. A possible explanation in both cases is that direct and reflected sound take different propagation paths. The direct sound at both the Barrier and No Barrier sites is likely experiencing ground effects/wave interference that cause a dip in sound level in that frequency range. The reflected sound at the barrier site is experiencing a different propagation path than the direct sound, with different ground effects and wave interference with ground reflections; a dip in the 250-500 Hz range would be nonexistent or diminished. The lower graph compares the levels at the higher BarCom04 and NoBarCom06 positions. The low- frequency levels are higher for BarCom04, but only by a maximum of 2 dB at 160 Hz. The BarCom04 level is slightly higher than the NoBarCom06 level across the rest of the spectrum, but by no more than 1 dB at 400 Hz and 6.3 kHz. The difference at 315 Hz is 0 dB compared to 6 dB at the lower-height microphones.

C-28 Figure 24. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), all microphones, for all Downwind Neutral groups, MD-5. -4.0 -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups

C-29 For the sound-absorbing I-70 barrier, Figure 25 shows in the upper graph that , in general, the BarRef01 levels are less than 1 dB higher than the NoBarRef02 levels across most of the spectrum, from 80 Hz through 3.15 kHz. Below 63 Hz, the BarRef01 levels are from 1 dB to 3 dB higher, and above 3.15 kHz, 1.2 dB to 2 dB higher. The field notes offer no explanation for these larger differences in these low- and high-frequency bands. The middle graph shows the differences in levels between BarCom03 and NoBarCom05, both of which were 5 ft. above the ground and 11 ft. above the roadway elevation. Over most of the spectrum between 80 Hz and 5.0 kHz, the BarCom03 levels are 0 dB to 1.0 dB higher than the NoBarCom05 levels. The exceptions are: at 315 Hz and 400 Hz, where the BarCom03 levels are approximately 3 dB higher than at NoBarCom05; and at 200 Hz and 250 Hz, where the BarCom03 levels are lower than the NoBarCom05 levels by 0.5 dB to 1.0 dB. The site conditions were similar at the BarCom03 and NoBarCom05 sites, providing no clear explanation for the effects in the 200 Hz to 400 Hz bands, nor at the low and high ends of the spectrum. The lower graph compares the levels at BarCom04 and NoBarCom06, which were 10 ft. above the ground and 16 ft. above the roadway elevation. Over most of the spectrum between 50 Hz and 4.0 kHz, the BarCom04 levels are 0 dB to 1.1 dB higher than the NoBarCom06 levels. The exceptions are from 160 Hz to 315 Hz, where the BarCom04 levels range from 1.5 dB to 2.4 dB higher. Also, from 3.15 Hz to 6.3 kHz, the BarCom04 levels are lower than the NoBarCom06 levels by approximately 0.7 dB. Above 4 kHz, the BarCom04 levels are 1.5 dB to 5.0 dB higher than at NoBarCom06. No apparent reason exists for the substantial differences at the highest frequencies, although the differences are not that important since the sound pressure levels at these frequencies at both sites are much lower than at the middle frequencies.

C-30 Figure 25. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), all microphones, for all Calm Lapse groups, I-70. -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarRef01 - NoBarRef02 All CLG Groups -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarCom03 - NoBarCom05 All CLG Groups -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarCom04 - NoBarCom06 All CLG Groups

C-31 Community Microphones at Different Distances The I-90, SR-71, and I-75 locations had the community microphones pairs at different distances from each other. In general, the I-90 and SR-71 sound-reflecting barrier results showed greater differences in Barrier/No Barrier levels at the community microphones than for the sound-absorbing I-75 barrier. For I-90, Figure 26 shows the averages of the differences in the Barrier and No Barrier microphones’ levels for all the Calm Neutral groups. In the upper graph, in general, the BarRef01 levels are 0 dB to 1 dB higher than the NoBarRef02 levels at 400 Hz and below. Above 400 Hz and through 3.15 kHz, these levels are 0.5 dB to 1 dB higher than the NoBarRef02 levels. Above 4 kHz, the No Barrier levels are higher, likely due to localized insect noise. The middle graph compares the levels at BarCom03 and NoBarCom05, the lower-height microphones, both of which were 69 ft. from the center of the near travel lane and 10.4 ft. above the roadway surface. The levels in the frequency bands from 20 Hz through 80 Hz were 0.5 dB to 1 dB higher at BarCom03. For 1 kHz and higher, the BarCom04 levels were approximately 1 dB to 2 dB higher than those at NoBarCom05. The most noticeable differences were in the 250 Hz to 500 Hz bands, where the levels were 2.5 dB to 5 dB (at 400 Hz) higher. As noted in the MD-5 discussion above, a possible explanation for the barrier effect being prominent in the low-frequency range (250 Hz to 500 Hz) for BarCom03 at I-90 is that direct and reflected sound take different propagation paths with different ground effects and wave interference with ground reflections. The lower graph compares the levels at BarCom04 and NoBarCom06, both of which were 93 ft. from the center of the near travel lane and 17 ft. above the roadway surface. The levels in the frequency bands from 31.5 Hz through 250 Hz were 0.5 dB to 1 dB higher at BarCom04. From 1.25 kHz to 3.15 kHz, the BarCom04 levels were approximately 0.5 dB higher. The most noticeable differences were in the 315 Hz to 630 Hz bands, where the levels were 1.5 dB to 3 dB (at 400 Hz) higher.

C-32 Figure 26. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), BarCom03 minus NoBarCom05, for all Calm Neutral groups, I-90. -4.0 -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All CNG Groups -2.0 0.0 2.0 4.0 6.0 8.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 kD iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All CNG Groups -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All CNG Groups

C-33 For SR-71 (sound-reflecting barrier), Figure 27 shows the averages of the differences in the Barrier and No Barrier microphones’ levels for all the Downwind Neutral groups. The upper graph shows that the BarRef01 levels are higher than the NoBarRef02 levels across almost the entire spectrum, except for 8 kHz and 10 kHz. Because the BarRef01 microphone was in front of the barrier, higher levels were expected than at NoBarRef02. The BarRef01 levels are higher by 3 dB at 31.5 Hz, 2.5 dB at 125 Hz, and 1.5 dB at 2.5 kHz. In the range from 400 Hz to 1.25 kHz, the differences are less than 0.5 dB. The middle graph compares the levels at BarCom03 and NoBarCom05, which were close to SR71 on the opposite side of the road from the barrier. The levels at BarCom03 are generally higher than or the same as those at NoBarCom05. The levels in the frequency bands from 20 Hz through 125 Hz are 0.5 dB to 1.5 dB higher at BarCom03. From 160 Hz through 1.6 kHz, the levels are different by only 0.5 dB or less. From 2 kHz through 5 kHz, the BarCom03 level are one-half decibel higher than NoBarCom05. The NoBarCom05 levels are less than 1.5 dB higher than BarCom03 at and above 6.3 kHz. The lower graph compares the levels at the distant BarCom04 and NoBarCom06 positions. The levels in the frequency bands from 20 Hz through 80 Hz were 2 dB to 4 dB higher at BarCom04 compared to NoBarCom06. Then, from 315 Hz through 8 kHz, the BarCom04 levels are 1.5 dB to 3 dB higher than NoBarCom06. In the range of 100 Hz through 250 Hz, the NoBarCom06 levels range from 0 dB to 3 dB (at 200 Hz) higher than the BarCom04 levels.

C-34 Figure 27. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), all microphones, for all Downwind Neutral groups, SR-71. -4.0 -2.0 0.0 2.0 4.0 6.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups -4.0 -2.0 0.0 2.0 4.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz All DNG Groups

C-35 For the sound-absorbing I-75 barrier, Figure 28 shows the results for an average of all the Calm Inversion groups. In the upper graph, the BarRef01 levels are approximately 0.6 dB to 2.7 dB higher than the NoBarRef02 levels across the entire spectrum, except at 20 Hz, where the difference is only 0.2 dB. From 80 Hz to 400 Hz, the difference is 2 dB or more; from 500 Hz to 1,600 Hz, the difference is 1 dB or less. These bands are those for which the sound-absorbing material would be expected to be most effective. Above 2 kHz, the difference is over 1.5 dB. The middle graph shows the differences in levels between BarCom03 and NoBarCom05, both of which were 10 ft. above the roadway elevation. Through 1.25 kHz, the BarCom03 levels are within +/- 1 dB of the NoBarCom05 levels (being slightly lower than NoBarCom05 at 125 Hz and 160 Hz). At 1.6 kHz and 2 kHz, the BarCom03 levels are 1.3 dB and 1.0 dB higher than at NoBarCom05, while the NoBarCom05 levels are slightly higher than BarCom03 above 3.15 kHz. In any case, the levels in these higher frequencies are much lower than in the middle frequencies. The lower graph compares the levels at BarCom04 and NoBarCom06, both of which were 20 ft. above the roadway surface and farther away than BarCom03 and NoBarCom05. Through 2.0 kHz, the BarCom04 levels are from 0 dB to 1.1 dB higher than at NoBarCom06. From 2.5 kHz to 5.0 kHz, the NoBarCom06 levels are 0.5 dB to 1.1 dB higher than those at BarCom04, while above 6.3 kHz, they are 0.8 dB to 1.0 dB lower. The reason for NoBarCom06 being higher in some of the higher frequencies is not clear since no insects were present.

C-36 Figure 28. Averages of the differences in Leq (5 min.) +/- one standard deviation (dB), all microphones, for all Calm Inversion groups, I-75. -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarRef01 - NoBarRef02 All CIG Groups -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarCom03 - NoBarCom05 All CIG Groups -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 dB A d BZ 2 0 2 5 3 1. 5 4 0 5 0 6 3 8 0 1 00 1 25 1 60 2 00 2 50 3 15 4 00 5 00 6 30 8 00 1 k 1. 25 k 1. 6k 2k 2. 5k 3. 15 k 4k 5k 6. 3k 8k 10 k D iff er en ce in L ev el , d B 1/3 Octave Band Frequency, Hz BarCom04 - NoBarCom06 All CIG Groups

C-37 C H A P T E R C - 6 Broadband L90 and L99 Statistical Descriptors In addition to the examination of the differences in levels for the equivalent pairs of running 5-minute Leq data, the differences in the Ln des criptors for the overall data without segregation into equivalent periods were investigated. The focus was on the possible change in the background level in the presence of the noise barrier. Community Microphones at Same Distances and Different Heights At the I-24 (sound-reflecting barrier), MD-5 (sound-reflecting barrier), and I-70 (sound-absorbing barrier) locations, the community microphones were at the same distances from the road, but at different heights above the road. Evidence of elevated background levels is strong for the I-24 reference microphone position in front of the barrier. To a lesser degree, background levels are elevated opposite the I-24 barrier and, in the daytime, the MD-5 barrier (the nighttime background at MD-5 was dominated by frog noise). Mixed evidence exists of elevated background opposite the sound-absorbing I-70 barrier. For I-24, Figure 29 presents the reference microphone differences in L90 (5 min.) and L99 (5 min.) along with Leq (5 min.), computed as BarRef01 minus NoBarRef02 for the A-weighted sound levels. The results show that while the Leq (5 min.) averages about 1 dB higher at BarRef01 than at NoBarRef02, the L90 and L99 at BarRef01 are much higher than at NoBarRef02. This effect on these two descriptors is evidence of an increase in the background level in front of the barrier that could be attributed to the presence of reflected sound rays reaching the mic in addition to the direct rays from the passing vehicles. The results support the idea of not only a reflection component during the moment of passage, but also approach and receding components of the reflections. Thus, the sound level rises sooner and recedes later for each vehicle. This sustained sound for a single vehicle overlaps with the same pattern for other vehicles, elevating the background level and reducing the time during which the background level might decrease between vehicle passages. Figure 30 presents the differences for BarCom03 and NoBarCom05 (the lower microphones across from the barrier), computed as BarCom03 minus NoBarCom05. Less evidence exists of the elevated background level at BarCom03 compared to NoBarCom05, which is expected given the dominance of the direct sound from the close-by traffic. Figure 31 presents the differences for BarCom04 and NoBarCom06 (the upper microphones across from the barrier), computed as BarCom04 minus NoBarCom06. More evidence exists of the elevated background levels at BarCom04 compared to BarCom03 because of the elevated position of the microphone, leading to less shielding of the reflected noise by the median parapet.

C-38 Figure 29. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-24, BarRef01 and NoBarRef02. Figure 30. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-24, BarCom03 and NoBarCom05. -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7S ou nd L ev el d iff er en ce , d B Time L90 L99 Leq -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7 So un d Le ve l d iff er en ce , d B Time L90 L99 Leq

C-39 Figure 31. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-24, BarCom04 and NoBarCom06. For MD-5 (sound-reflecting barrier), Figure 32 presents the differences in L90 (5 min.) and L99 (5 min.) along with Leq (5 min.) for the A-weighted sound levels for BarCom03 and NoBarCom05 (the lower microphones across from the barrier), computed as BarCom03 minus NoBarCom05. Evidence of the elevated background level is present at BarCom03 during the daytime hours. While the Leq (5 min.) averages about 1 dB higher than NoBarCom05, the L90 (5 min.) at BarCom03 ranges from 2 dB lower to 8 dB higher than NoBarCom05, averaging approximately 3 dB higher. Almost all the daytime L99 (5 min.) are higher at BarCom03 than NoBarCom05, which is evidence of an increase in the background sound level due to reflected sound off the barrier. As noted at the other locations, none of these levels have been edited for contaminating sounds. In the evening, the clear trend was for the L90 (5 min.) and L99 (5 min.) at NoBarCom05 to grow louder relative to BarCom03 as the evening got later. This trend is a result of the increased level and constancy of frog and insect noise. Figure 33 presents the MD-5 differences for BarCom04 and NoBarCom06 (the upper microphones across from the barrier), computed as BarCom04 minus NoBarCom06. Mixed evidence exists of the elevated background level at BarCom04 compared to NoBarCom06 during the daytime. For the first part of the afternoon measurements, the NoBarCom06 background level appears to be higher than that at BarCom04. For the second part of the afternoon measurements, the reverse appears to be true. In the evening, there is compelling evidence of elevated background level at NoBarCom06 due to frog and insect noise in the No Barrier area. -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 13 :1 3 13 :2 2 13 :3 1 13 :4 0 13 :4 9 13 :5 8 14 :0 7 14 :1 6 14 :2 5 14 :3 4 14 :4 3 14 :5 2 15 :0 1 15 :1 0 15 :1 9 15 :2 8 15 :3 7 15 :4 6 15 :5 5 16 :0 4 16 :1 3 16 :2 2 16 :3 1 16 :4 0 16 :4 9 16 :5 8 17 :0 7 So un d Le ve l d iff er en ce , d B Time L90 L99 Leq

C-40 Figure 32. Differences in broadband A-weighted 5-minute L90, L99 and Leq, MD-5, BarCom03 and NoBarCom05. Figure 33. Differences in broadband A-weighted 5-minute L90, L99 and Leq, MD-5, BarCom04 and NoBarCom06. -12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 12 :0 0 12 :1 8 12 :3 6 12 :5 4 13 :1 2 13 :3 0 13 :4 8 14 :0 6 14 :2 4 14 :4 2 15 :0 0 15 :1 8 15 :3 6 15 :5 4 19 :4 9 20 :0 7 20 :2 5 20 :4 3 21 :0 1 21 :1 9 21 :3 7 21 :5 5 22 :1 3 22 :3 1 22 :4 9 23 :0 7 23 :2 5 23 :4 3 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 12 :0 0 12 :1 8 12 :3 6 12 :5 4 13 :1 2 13 :3 0 13 :4 8 14 :0 6 14 :2 4 14 :4 2 15 :0 0 15 :1 8 15 :3 6 15 :5 4 19 :4 9 20 :0 7 20 :2 5 20 :4 3 21 :0 1 21 :1 9 21 :3 7 21 :5 5 22 :1 3 22 :3 1 22 :4 9 23 :0 7 23 :2 5 23 :4 3 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-41 For the sound-absorbing I-70 barrier, Figure 34 presents the reference microphone differences, computed as BarRef01 minus NoBarRef02. The results show that while the A-weighted Leq (5 min.) data average about 0.5 dB higher at BarRef01 than at NoBarRef02, the L90 at BarRef01 range from 0 dB to 2 dB higher than at NoBarRef02 up until around 17:00. It then fluctuates from 1 dB lower to 2 dB higher than at NoBarRef02 through the end of data collection around 18:30. Less of a trend exists for the L99, with the BarRef01 value ranging above and below that for NoBarRef02 over the entire period. Thus, the first two hours of the L90 data suggest an increase in the background sound level in front of the barrier that could be attributed to the presence of reflected sound rays reaching the microphone in addition to the direct rays from the passing vehicles. However, the later L90 data and the L99 data do not support that conclusion. Figure 34. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-70, BarRef01 and NoBarRef02. Figure 35 presents the differences for BarCom03 and NoBarCom05 (the lower microphones across from the barrier), computed as BarCom03 minus NoBarCom05. As with the reference microphones, on average, the Leq (5 min.) is on the order of 0 dB to 1 dB higher at the barrier site. Likewise, during the first two hours of data collection the L90 are slightly higher at BarCom03 compared to NoBarCom05, but the differences fluctuate (positively and negatively) during the last two hours. Also, there is no trend in the L99 data, with a range in differences from -5 dB to nearly +6 dB. Figure 36 presents the I-70 barrier differences in L90 (5 min.) and L99 (5 min.) along with Leq (5 min.) for the A-weighted sound levels for BarCom04 and NoBarCom06 (the upper microphones across from the barrier), computed as BarCom04 minus NoBarCom06. The results are like the other microphone pairings: slightly higher Leq (5 min.); slightly higher L90 during the first half of data collection; and no trend in the L99 data. -6 -4 -2 0 2 4 6 8 14 :3 5 14 :4 4 14 :5 3 15 :0 2 15 :1 1 15 :2 0 15 :2 9 15 :3 8 15 :4 7 15 :5 6 16 :0 5 16 :1 4 16 :2 3 16 :3 2 16 :4 1 16 :5 0 16 :5 9 17 :0 8 17 :1 7 17 :2 6 17 :3 5 17 :4 4 17 :5 3 18 :0 2 18 :1 1 18 :2 0 18 :2 9 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-42 Figure 35. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-70, BarCom03 and NoBarCom05. Figure 36. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-70, BarCom04 and NoBarCom06. -6 -4 -2 0 2 4 6 8 14 :3 5 14 :4 5 14 :5 5 15 :0 5 15 :1 5 15 :2 5 15 :3 5 15 :4 5 15 :5 5 16 :0 5 16 :1 5 16 :2 5 16 :3 5 16 :4 5 16 :5 5 17 :0 5 17 :1 5 17 :2 5 17 :3 5 17 :4 5 17 :5 5 18 :0 5 18 :1 5 18 :2 5 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq -6 -4 -2 0 2 4 6 8 15 :2 0 15 :3 0 15 :4 0 15 :5 0 16 :0 0 16 :1 0 16 :2 0 16 :3 0 16 :4 0 16 :5 0 17 :0 0 17 :1 0 17 :2 0 17 :3 0 17 :4 0 17 :5 0 18 :0 0 18 :1 0 18 :2 0 18 :3 0 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-43 Community Microphones at Different Distances The I-90 (sound-reflecting barrier), SR-71 (sound-reflecting barrier), and I-75 (sound-absorbing barrier) locations are discussed here. Strong evidence exists of elevated background levels for the I-90 community microphones and the SR-71 reference position. These differences could be attributed to the presence of reflected sound rays from the passing vehicles reaching the microphone in addition to the direct rays, producing a sustained sound that keeps the background level from dropping off during gaps between vehicles. Strong evidence exists of elevated background sound level at the more distant SR-71 community microphone in addition to the elevated Leq. There is mixed evidence of increased background levels at community microphones opposite the I-75 sound-absorbing barrier. For I-90, Figure 37 presents the differences in L90 (5 min.) and L99 (5 min.) along with Leq (5 min.) for the A-weighted sound levels, computed as BarCom03 minus NoBarCom05. While the Leq (5 min.) averages about 0.5 dB to 1 dB higher than NoBarCom05, the L90 at BarCom03 are 1 dB to 2 dB higher, and the L99 at BarCom03 are 1 dB to 4 dB higher. Figure 38 presents the differences for BarCom04 and NoBarCom06 (the upper microphones across from the barrier), computed as BarCom04 minus NoBarCom06. Strong evidence exists of the elevated background level at BarCom04 compared to NoBarCom06, with the differences similar to the BarCom03 comparison to NoBarCom05. Figure 37. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-90, BarCom03 and NoBarCom05. -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 13 :0 0 13 :0 9 13 :1 8 13 :2 7 13 :3 6 13 :4 5 13 :5 4 14 :0 3 14 :1 2 14 :2 1 14 :3 0 14 :3 9 14 :4 8 14 :5 7 15 :0 6 15 :1 5 15 :2 4 15 :3 3 15 :4 2 15 :5 1 16 :0 0 16 :0 9 16 :1 8 16 :2 7 16 :3 6 16 :4 5 16 :5 4 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-44 Figure 38. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-90, BarCom04 and NoBarCom06. For SR-71 (sound-reflecting barrier), Figure 39 presents the reference microphone differences in L90 (5 min.) and L99 (5 min.) along with Leq (5 min.), computed as BarRef01 minus NoBarRef02 for the A-weighted sound levels. Much like the I-24 data, the results show that while the Leq (5 min.) averages about 0 dB to 1 dB higher at BarRef01 than at NoBarRef02, the L90 (5 min.) and L99 (5 min.) at BarRef01 are much higher than at NoBarRef02: L90 by as much as 4 dB and L99 by as much as 7 dB. Figure 40 presents the differences at the microphones close to the road, computed as BarCom03 minus NoBarCom05. Strong evidence exists of the elevated background level at BarCom03 compared to NoBarCom05 even though these two microphones are close to the edge of the shoulder across from the barrier. While the Leq (5 min.) at BarCom03 ranges about 0.5 dB higher to 1 dB lower than NoBarCom05, the L90 at BarCom03 are, on average, about 1 dB higher than NoBarCom05, and the L99 at BarCom03 average approximately 1.5 dB higher. For both descriptors, there are also times when the NoBarCom05 levels are higher than the BarCom03 levels. Nonetheless, on average, the trend is for the L90 and L99 to be higher at the Barrier microphone. As observed by the researchers when listening to the audio recordings across from the barrier, there was a change in the character of the sound that gave the sensation that a barrier was in place at the Barrier site. Figure 41 presents the differences for the distant microphones, computed as BarCom04 minus NoBarCom06. This figure starts 45 minutes into the measurement period because there was a great deal of roofing nail gun noise audible at NoBarCom06 during that initial time. The results are different for this microphone pair than most of the other pairs across the other study locations because these microphones are the farthest from the road. The BarCom04 Leq (5 min.) ranged from 2.5 dB to 3.8 dB higher than the NoBarCom06 level for the first 23 minutes of the period shown on the figures. During this time, the L90 (5 min.) and L99 (5 min.) differences ranged from 2 dB to 5 dB higher at BarCom04 than at NoBarCom06. During this period, the meteorological class was Calm Neutral. During the last three hours, the Leq (5 min.) difference became more variable, from 0.5 dB to 2.5 dB higher at BarCom04. During this period, L90 (5 min.) differences also became more variable, being 0 dB to 3.5 dB higher at BarCom04. The L99 (5 min.) became even more variable, with the BarCom04 values ranging from 1 dB lower than those at -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 13 :0 0 13 :0 9 13 :1 8 13 :2 7 13 :3 6 13 :4 5 13 :5 4 14 :0 3 14 :1 2 14 :2 1 14 :3 0 14 :3 9 14 :4 8 14 :5 7 15 :0 6 15 :1 5 15 :2 4 15 :3 3 15 :4 2 15 :5 1 16 :0 0 16 :0 9 16 :1 8 16 :2 7 16 :3 6 16 :4 5 16 :5 4 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-45 NoBarCom06 to 5.4 dB higher. During this time period, the meteorological class was Downwind Neutral. On average, and over the full measurement period, the BarCom04 Leq (5 min.), L90 (5 min.), and L99 (5 min.) were 1.7 dB, 2.0 dB, and 2.1 dB higher than at NoBarCom06. As a whole, the results suggest the overall levels from the traffic noise are higher at the Barrier site, but because the traffic was 400 ft. away, there is less overall rise and fall to the levels compared to being close to the road. As a result, there is little chance for lulls in the noise under the studied traffic flows. Figure 39. Differences in broadband A-weighted 5-minute L90, L99 and Leq, SR-71, BarRef01 and NoBarRef02. Figure 40. Differences in broadband A-weighted 5-minute L90, L99 and Leq, SR-71, BarCom03 and NoBarCom05. -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9: 00 9: 10 9: 20 9: 30 9: 40 9: 50 10 :0 0 10 :1 0 10 :2 0 10 :3 0 10 :4 0 10 :5 0 11 :0 0 11 :1 0 11 :2 0 11 :3 0 11 :4 0 11 :5 0 12 :0 0 12 :1 0 12 :2 0 12 :3 0 12 :4 0 12 :5 0 13 :0 0 13 :1 0 13 :2 0S ou nd L ev el D iff er en ce , d B Time L90 L99 Leq -4 -3 -2 -1 0 1 2 3 4 5 6 9: 00 9: 10 9: 20 9: 30 9: 40 9: 50 10 :0 0 10 :1 0 10 :2 0 10 :3 0 10 :4 0 10 :5 0 11 :0 0 11 :1 0 11 :2 0 11 :3 0 11 :4 0 11 :5 0 12 :0 0 12 :1 0 12 :2 0 12 :3 0 12 :4 0 12 :5 0 13 :0 0 13 :1 0 13 :2 0 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-46 Figure 41. Differences in broadband A-weighted 5-minute L90, L99 and Leq, SR-71, BarCom04 and NoBarCom06. For the sound-absorbing I-75 barrier, Figure 42 presents the reference microphone differences in the A-weighted L90 (5 min.), L99 (5 min.), and Leq (5 min.), computed as BarRef01 minus NoBarRef02. The results show that while the Leq (5 min.) are from 0.1 dB to 1.7 dB higher at BarRef01 than at NoBarRef02, almost all the L90 at BarRef01 are higher than at NoBarRef02, with a range from -0.5 dB to 3.1 dB, except for some large differences of 3 dB to 5.5 dB in the period from approximately 20:20 to 20:48 (a review of the field notes offered no explanation of unusual activity during that time). The L99 differences are more variable: less than one-quarter of the L99 are lower at BarRef01 than at NoBarRef02; the rest are higher than at NoBarRef02, with the unexplained large differences from around 20:20 to 20:48, as seen in the L90 data. The generally higher L90 at BarRef01 than at NoBarRef02 suggests an increase in the background level in front of the barrier that could be due to the presence of reflected sound rays reaching the microphone in addition to the direct rays from the passing vehicles. However, those times when the L99 is lower at BarRef01 than at NoBarRef02 do not support this theory. -2 -1 0 1 2 3 4 5 6 9: 45 9: 55 10 :0 5 10 :1 5 10 :2 5 10 :3 5 10 :4 5 10 :5 5 11 :0 5 11 :1 5 11 :2 5 11 :3 5 11 :4 5 11 :5 5 12 :0 5 12 :1 5 12 :2 5 12 :3 5 12 :4 5 12 :5 5 13 :0 5 13 :1 5 13 :2 5 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-47 Figure 42. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-75, BarRef01 and NoBarRef02. Figure 43 presents the differences at I-75 for BarCom03 and NoBarCom05 (the closer microphones across from the barrier), computed as BarCom03 minus NoBarCom05. While the Leq (5 min.) are generally slightly higher at BarCom03 than at NoBarCom05, the L90 and L99 differences are much more variable. The A-weighted L90 ranges from 2 dB lower to 2.5 dB higher at BarCom03 compared to NoBarCom05, while the A-weighted L99 fall in a +/-4 dB range from 0.5 dB to 1.5 dB higher at BarRef01 than at NoBarRef02. Figure 44 presents the differences at I-75 for BarCom04 and NoBarCom06 (the more distant microphones across from the barrier), computed as BarCom04 minus NoBarCom06. The results for this microphone pair are like those for BarCom03 and NoBarCom05, with little evidence of a consistent elevation of the background level at BarCom04 compared to NoBarCom06. -2 -1 0 1 2 3 4 5 6 7 8 17 :1 2 17 :2 1 17 :3 0 17 :3 9 17 :4 8 17 :5 7 18 :0 6 18 :1 5 18 :2 4 18 :3 3 18 :4 2 18 :5 1 19 :0 0 19 :0 9 19 :1 8 19 :2 7 19 :3 6 19 :4 5 19 :5 4 20 :0 3 20 :1 2 20 :2 1 20 :3 0 20 :3 9 20 :4 8 20 :5 7 21 :0 6 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-48 Figure 43. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-75, BarCom03 and NoBarCom05. Figure 44. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-75, BarCom04 and NoBarCom06. -5 -4 -3 -2 -1 0 1 2 3 4 5 17 :1 2 17 :2 2 17 :3 2 17 :4 2 17 :5 2 18 :0 2 18 :1 2 18 :2 2 18 :3 2 18 :4 2 18 :5 2 19 :0 2 19 :1 2 19 :2 2 19 :3 2 19 :4 2 19 :5 2 20 :0 2 20 :1 2 20 :2 2 20 :3 2 20 :4 2 20 :5 2 21 :0 2 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq -5 -4 -3 -2 -1 0 1 2 3 4 5 17 :1 2 17 :2 2 17 :3 2 17 :4 2 17 :5 2 18 :0 2 18 :1 2 18 :2 2 18 :3 2 18 :4 2 18 :5 2 19 :0 2 19 :1 2 19 :2 2 19 :3 2 19 :4 2 19 :5 2 20 :0 2 20 :1 2 20 :2 2 20 :3 2 20 :4 2 20 :5 2 21 :0 2 So un d Le ve l D iff er en ce , d B Time L90 L99 Leq

C-49 C H A P T E R C - 7 Ln Descriptors for One-Third Octave Bands The preceding analysis was for the broadband A-weighted sound levels and unweighted sound pressure levels. The following analysis examines the data in terms of one-third octave bands by use of color shading. In the figures, the brown color means that the Barrier levels are higher than the No Barrier levels and blue means that No Barrier levels are higher. In each graph, time runs from top to bottom with the total block representing approximately four hours. Each row represents the starting minute of a 5-minute averaging block of time. The one-third octave bands run from left to right, with the broadband A-weighted sound levels and unweighted sound pressure levels as the first two “columns” on the far left. Within each band’s column of data are the differences for seven sound pressure level Ln values and Leq (left to right: L1, L5, L10, L33, L50, L90, L99, and Leq). Figure 45 compares the reference microphone levels for I-24 (sound-reflecting barrier). The vertical brown streaks on the right sides of the data columns in the frequency bands from 400 Hz through 2 kHz for most of the sample period and through 5 kHz for the first half of the sample period represent higher L90 (5 min.) and L99 (5 min.) values at BarRef01 than at NoBarRef02. These higher background levels are evidence of the sustaining of a vehicle’s pass-by noise due to the creation of an image source for each vehicle as the sound reflects off the barrier. In contrast, the vertical blue streaks in the 8-kHz band are evidence of elevated background levels at the NoBarRef02, likely due to insect noise in the vegetation behind this position. Figure 45. I-24 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02.

C-50 Figure 46 presents the I-24 Ln differences for BarCom03 and NoBarCom05, while Figure 47 presents the Ln differences for BarCom04 and NoBarCom06. Some evidence exists of slightly higher Ln values at BarCom03 vs. NoBarCom05 in the 315 Hz to 800 Hz bands and at BarCom04 vs. NoBarCom06 over much of the lower-frequency range. The strong blue streaks in the 6.3-kHz and 8-kHz bands indicate elevated background levels at the No Barrier microphones due to insect noise in the vegetation behind these microphones. Figure 46. I-24 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05. Figure 47. I-24 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06.

C-51 For I-90 (sound-reflecting barrier), Figure 48 compares BarRef01 and NoBarRef02 levels. As expected, there is little evidence of elevated background levels due to sound reflections at BarRef01 compared to NoBarRef02 because the BarRef01 microphone was atop the barrier. The blue color in the bands at and above 4 kHz is evidence of insect noise near the NoBarRef02 position. Figure 48. I-90 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02. Figure 49 presents the I-90 Ln differences for BarCom03 and NoBarCom05, while Figure 50 presents the I-90 Ln differences for BarCom04 and NoBarCom06. The brown color in the 250 Hz to 500 Hz range indicates an increase in all the Ln descriptors, meaning the BarCom03 levels are higher than the NoBarCom05 levels. Vertical brown streaks on the right sides of the data columns in the frequency bands from 630 Hz to 3.15 kHz mean that the BarCom03 background levels are higher than the NoBarCom05 background levels., suggesting the reflected sound is sustaining the background level opposite the barrier. Figure 50 contains much less brown, showing that the BarCom04 upper microphone levels are not that much higher than the NoBarCom06 levels. The blue color in the 20 Hz to 31.5 Hz bands and the bands at and above 4 kHz band show the NoBarCom06 levels to be higher than at BarCom04 at these frequencies. Figure 49. I-90 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05.

C-52 Figure 50. I-90 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06. Figure 51 compares the SR-71 BarRef01 and NoBarRef02 levels. Vertical brown streaks on the right sides of the data columns indicate higher L90 (5 min.) and L99 (5 min.) at BarRef01 in the frequency bands from 500 Hz through 4 kHz for nearly all the sample period, and through 5 kHz for the first half of the sample period. These are evidence of a sustaining of a vehicle’s pass-by noise due the reflected sound, similar to I-24, where that location’s BarRef01 microphone was also between the barrier and the road. Figure 51. SR-71 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02. Figure 52 presents the SR-71 spectral Ln differences for BarCom03 and NoBarCom05. Not much difference is seen between the descriptors for the two microphones, which is consistent with A-weighted sound level graphs. An exception is the L90 and L99 background levels in the 1 kHz to 4 kHz bands, where there appears to be a general trend for the BarCom03 values to be higher than NoBarCom05 values, evidence of an elevated background in these bands. Figure 53 presents the SR-71 spectral Ln differences for distant BarCom04 and NoBarCom06 positions. A pattern can be seen of higher broadband A-weighted levels at BarCom04 in the lower bands and mid-to- upper bands, with higher NoBarCom06 levels in the 100 Hz to 250 Hz bands and the highest-frequency bands. This pattern applies across most of the Ln descriptors, not just L90 (5 min.) and L99 (5 min.).

C-53 Figure 52. SR-71 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05. Figure 53. SR-71 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06. For MD-5 (sound-reflecting barrier), Figure 54 compares BarRef01 and NoBarRef02. At MD-5, there were two measurement sessions (in the afternoon and at night), hence the two blocks of data in the figure. The most obvious difference is the large increase in the background levels at NoBarRef02 (blue color) in the night due to the frog noise. This elevated background level also shows up in the broadband A-weighted and unweighted levels on the left of the figure. Some evidence exists of higher background levels at BarRef01 in the afternoon session in the bands from 630 Hz through 2.5 kHz, as evidenced by the brown streaks on the right side of the one-third octave band columns of data.

C-54 Figure 54. MD-5 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02. Figure 55 presents the MD-5 Ln differences for BarCom03 and NoBarCom05, the lower microphones. The brown bands show increases in the BarCom03 levels relative to those for NoBarCom05 across most of the Ln descriptors in the bands centered on 250 through 400 Hz, interpreted as evidence of increases in sound pressure levels due to reflections off the barrier. The daytime data also show higher levels at BarCom03 in the background Ln values for L90 and L99 for the bands from 500 Hz through 3,150 Hz, as indicated by the brown streaks on the right side of those bands’ columns. The blue streaks in the night’s high-frequency bands represent the frog and insect noise in the No Barrier area.

C-55 Figure 55. MD-5 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05. Figure 56 presents the MD-5 Ln differences for BarCom04 and NoBarCom06, the upper microphones. The brown areas show increases in the BarCom03 levels relative to those for NoBarCom05 across most of the Ln descriptors in the bands centered on 100 Hz through 160 Hz. The daytime data also show higher levels at BarCom03 in the background Ln values for L90 and L99 for the bands from 630 Hz through 2.5 kHz, as indicated by the brown streaks on the right side of those bands’ columns. The blue bands in the night’s high-frequency bands again represent the frog and insect noise in the No Barrier area. The latter part of the evening sampling for L1 and Leq includes two horizontal lines of blue shading for L1 and Leq, which indicate a short-term loud event at NoBarCom06 that did not occur at the BarCom04 site.

C-56 Figure 56. MD-5 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06. For the sound-absorbing I-75 barrier, Figure 57 compares BarRef01 and NoBarRef02 levels. In general, the overall brownish tone to the figure indicates that the BarRef01 levels are higher than the NoBarRef02 levels across most of the frequencies and all Ln descriptors. In several higher frequency bands, there are occasional blue blocks for the L99 (5 min.) data at 3.15 kHz and above. The coloring is more neutral in the 500 Hz to 2 kHz bands, indicating little difference in the levels across the Ln descriptors; if anything, the BarRef01 L99 (5 min.) are somewhat elevated for some of the periods, although this trend is not consistent over most of the periods. An elevated L99 (5 min.) or L90 (5 min.) would be an indication that the BarRef01 background levels are higher than the NoBarRef02 background levels, evidence of a sustaining of a vehicle’s pass-by noise due to the creation of an image source for each vehicle as the sound reflects off the barrier.

C-57 Figure 57. I-75 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02. Figure 58 presents the I-75 Ln differences for BarCom03 and NoBarCom05. The lower frequencies (20 Hz through 63 Hz) and upper-middle frequencies (800 Hz through 2 kHz) are neutral to light brown, across most of the descriptors, suggesting no difference or slightly higher levels at BarCom03. The lower - middle lower frequencies (80 Hz through 315 Hz) and upper frequencies (2.5 kHz and above) are neutral to light blue across most of the descriptors, suggesting no difference or slightly higher levels at NoBarCom05. The exception is the L99 (5 min.) data at 4 kHz and above, which shows a stronger blue tone, meaning the background level at NoBarCom05 was consistently higher than at BarCom03. The results show no evidence of a sustaining of the sound due to reflected noise off the sound-absorbing barrier. Figure 59 presents the I-75 Ln differences for BarCom04 and NoBarCom06. Below 2 kHz, there is not strong color indication of higher levels at BarCom04, perhaps except for the 63 Hz to 100 Hz range. In the 2.5 kHz to 5.0 kHz bands, there is an indication of somewhat higher levels at NoBarCom06 than at BarCom04, across most of the Ln descriptors, with greater differences for the L99 descriptor. The field team did not notice any localized noise sources to explain the higher background levels at NoBarCom06, indicated by the higher L99 values. Figure 58. I-75 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05.

C-58 Figure 59. I-75 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06. For the sound-absorbing barrier at I-70, Figure 60 compares the BarRef01 and NoBarRef02 levels. In general, the overall brownish tone for the frequency bands of 20 Hz to 50 Hz and from 4 kHz to 10 kHz indicates that the BarRef01 levels are slightly higher than the NoBarRef02 levels across all Ln descriptors in those bands. In the upper frequency bands, the L99 (5 min.) columns show some periods of higher background levels at one microphone position and some higher periods at the other microphone—no clear trend. Across the rest of the spectrum from 80 Hz through 3.15 kHz, there is little difference in levels at the two microphone positions, with some indication of higher L99 (5 min.) at NoBarRef02 at 160 Hz, 200 Hz, and 3.15 kHz, and some indication of higher L99 (5 min.) at BarRef01 from 250 Hz through 630 Hz. Figure 60. I-70 Differences in Ln (5 min.) by one-third octave frequency bands: BarRef01 and NoBarRef02. Figure 61 presents the I-70 Ln differences for BarCom03 and NoBarCom05, the lower microphones. Again, brown means Barrier levels are higher and blue means the No Barrier levels are higher. All the Ln descriptors at BarCom03 are clearly higher than at NoBarCom05 in the 315 Hz and 400 Hz bands. In contrast, the L90 (5 min.) and L99 (5 min.) levels at NoBarCom05 are generally higher than at BarCom03 in the 160 Hz and 200 Hz bands, and at 250 Hz for the first half of the sample period. In many of the bands at and above 630 Hz, the L99 (5 min.) are higher at NoBarCom05. For the highest-frequency bands, the L1 (5 min.) and L5 (5 min.) descriptors are higher for the BarCom03 position. Figure 62 presents the I-70 Ln differences for BarCom04 and NoBarCom06. In the 200 Hz and 250 Hz bands, the BarCom04 levels are higher than those at NoBarCom06 for most of the descriptors. From 315 Hz through 2.5 kHz, the Ln descriptors are quite close to each other, with BarCom04 slightly higher than NoBarCom06. At 8 kHz and 10 kHz, the levels for all the descriptors are substantially higher at BarCom04 than at NoBarCom06.

C-59 Figure 61. I-70 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom03 and NoBarCom05. Figure 62. I-70 Differences in Ln (5 min.) by one-third octave frequency bands: BarCom04 and NoBarCom06.

C-60 C H A P T E R C - 8 Spectrograms Spectrograms show the frequency content of sound as a function of time. This section qualitatively compares Phase 1 and Phase 2 results of the spectrogram analysis before comparing the difference spectrograms. Data presented here are for 5-minute time blocks and vehicle pass-by events. A 5-minute data block for I-24 (sound-reflecting barrier) is presented first. Shown in Figure 63 are spectrograms for the reference positions and the high-microphone positions, comparing the Barrier and No Barrier sites. Figure 64 shows the same for the low-microphone positions. For the reference positions, there are more occurrences of higher sound levels (dark red) for the Barrier case compared to the No Barrier case. In addition, the higher sound level events are broader in frequency and time. Vehicles traveling eastbound dominate the sound levels, and during the 5-minute blocks, single events can be tracked from the Barrier site to the No Barrier site approximately 15 to 20 seconds later. For the high- and low-microphone positions across the highway from the barrier, there is indication that the higher sound level events are broader in frequency and time. Vehicles traveling westbound dominate the sound levels, and single events can be tracked from the No Barrier site to the Barrier site approximately 15 to 20 seconds later. The trend is not as obvious across the road from the barrier as for the reference positions, but it can be seen by focusing on a series of events and noticing that multiple consecutive events are more blended together in the Barrier case than the No Barrier case. As the higher levels (hot spots) broaden, they blend together more.

C-61 Figure 63. I-24 (sound-reflecting barrier) 5-minute spectrograms; top to bottom: BarRef01, NoBarRef02, high mics (BarCom04 and NoBarCom06); for Calm Lapse group CLG-6-1, start time 15:56.

C-62 Figure 64. I-24 (sound-reflecting barrier) 5-minute spectrograms; top to bottom: lows mics BarCom03 and NoBarCom05; for Calm Lapse group CLG-6-1, start time 15:56. Further evidence exists of higher sound level events being broader in frequency and time with closer examination of vehicle pass-by events. An example is shown in Figure 65, with a two-minute time block that includes a group of eastbound heavy trucks. The hot spots are broader in frequency and time.

C-63 Figure 65. I-24 (sound-reflecting barrier) spectrograms for a group of heavy trucks; top to bottom: BarRef01, NoBarRef02. Spectrograms from an I-90 (sound-reflecting barrier) vehicle pass-by event are shown in Figure 66, which has two plots of a heavy truck traveling southbound. The pass-by event is around 13:29:36 at the Barrier site and around 13:29:43 at the No Barrier site. These plots are for only the near microphones on

C-64 the community side of the highway, BarCom03 and NoBarCom05 (69 ft. from the center of the near travel lane). For the farther microphones (BarCom04/NoBarCom06), the results are similar to the BarCom03/NoBarCom05 pair, just with lower sound levels. The barrier reflection effect can be seen in the spectrograms for the heavy trucks traveling in either the northbound or southbound direction. For the Barrier site, the hot spots are wider and taller than for the No Barrier site for a broad range of frequencies. The tallest and darkest red band (highest sound level band) centered around 1,000 Hz is both wider and taller, with the same effect occurring in the surrounding frequency bands, stepping through various colors of the spectrum. This difference indicates that the barrier is causing higher sound levels at frequencies that contribute most to the overall sound level and causing these levels to be sustained for a longer period for each vehicle pass-by event. Figure 66. I-90 (sound-reflecting barrier) spectrograms for a heavy truck on southbound (community) side: top is BarCom03; bottom is NoBarCom05 (approximate event times: Barrier site 13:29:36, No Barrier site 13:29:43).

C-65 In addition to examining vehicle pass-by events at the I-90 location, spectrograms for larger blocks of data were studied. Figure 67 provides an example for the near microphones (BarCom03/NoBarCom05) for an hour-long data block starting at 15:30. Other blocks of data showed similar results. The farther microphones (BarCom04 and NoBarCom06) also showed similar results with lower sound levels. The spectrogram data show a clear difference between the Barrier and the No Barrier sites. As with the pass-by data, the clean data blocks show that hot spots are both wider and taller for a broad range of frequencies. Again, the tallest darkest red band (highest sound level band) centered around 1,000 Hz is both wider and taller at the barrier site, with the same effect occurring in the surrounding frequency bands, stepping through various colors of the spectrum. Again, this indicates that the barrier is causing higher sound levels at frequencies that contribute most to the overall sound level and causing these levels to be sustained for a longer period for each vehicle pass-by event. Figure 67. I-90 (sound-reflecting barrier) spectrograms for an hour-long block of data from 15:30 to 16:30: top is BarCom03; bottom is NoBarCom05.

C-66 For SR-71 (sound-reflecting barrier), spectrograms for a group of trucks traveling southbound are shown in Figure 68. The pass-by event is around 10:43:50 at the Barrier site and around 10:44:20 at the No Barrier site. Only shown are the far microphones—BarCom04 and NoBarCom06 (400 ft. from the center of the near travel lane). The barrier reflections effect for the heavy trucks can be seen clearly. For the barrier site, the hot spots are wider and taller for a broad range of frequencies. It is particularly noticeable for frequencies from 400 Hz to 2.5 kHz for the heavy trucks. Figure 68. SR-71 (sound-reflecting barrier) spectrograms for heavy trucks on southbound (community) side: top is BarCom04; bottom is NoBarCom06.

C-67 In addition to the vehicle pass-by events, blocks of data were also examined for SR-71. Figure 69 is for a 4-minute block of clean data in the morning at 09:49 and shows a clear difference between the Barrier and No Barrier sites at the far microphones. As with the pass-by data, the data block shows that hot spots are both wider and taller for a broad range of frequencies, particularly for 500 Hz and higher, the range to which barrier reflection effects can be attributed. The difference between Barrier and No Barrier A-weighted equivalent sound levels for this 4-minute block was 3.3 dB. Figure 69. SR-71 (sound-reflecting barrier) spectrograms for 4-minute block of data in the morning at 09:49: top is BarCom04; bottom is NoBarCom06.

C-68 Spectrograms for an MD-5 (sound-reflecting barrier) vehicle pass-by event are shown in Figure 70. A pickup truck traveling southbound passes around 20:09:20 at the Barrier site and 20:09:35 at the No Barrier site. The barrier reflections effect can be seen in the spectrograms. For the barrier site, the hot spots are wider and taller than for the No Barrier site for a broad range of frequencies. The darkest red areas (highest sound levels) fill in more and become wider and taller with the barrier present. For this event, the red is centered around 800 Hz or 1 kHz. The same effect occurs in the surrounding frequency bands, stepping through various colors of the spectrum. The intensifying and expanding hot spots indicate that the barrier is causing higher sound levels at frequencies that contribute most to the overall sound level and causing these levels to be sustained for a longer period for each vehicle pass-by event. Figure 70. MD-5 (sound-reflecting barrier) spectrograms for a pickup truck on southbound (barrier) side (approximate event times: Barrier site 20:09:20, No Barrier site 20:09:35). Top is BarCom04; bottom is NoBarCom06.

C-69 In addition to examining vehicle pass-by events, spectrograms for blocks of data were also examined at the MD-5 location. Figure 71 provides an example for the upper microphones (BarCom04/NoBarCom06) for a 41-minute data block starting at 13:15:00. Close examination shows the hot spots are both wider and taller for a broad range of frequencies. The highest levels are increasing in the 1 kHz region. Again, this indicates that the barrier is causing higher sound levels at frequencies that contribute most to the overall sound level and cause these levels to be sustained for a longer period for each vehicle pass-by event. Figure 71. MD-5 (sound-reflecting barrier) spectrograms for 41 minutes of clean data (no contamination from other noise sources): top is BarCom04; bottom is NoBarCom06.

C-70 Spectrograms for the sound-absorbing I-75 barrier location are discussed here. Figure 72 through Figure 74 are for a 5-minute time block from 17:55 to 18:00 for the barrier-side (reference) positions (Figure 72, Mics 1 and 2), the near-microphone community positions 50 ft. from edge of the nearest travel lane (Figure 73, Mics 3 and 5), and the far-microphone community positions 100 ft. from edge of the nearest travel lane (Figure 74, Mics 4 and 6). For the barrier-side reference positions, the hottest spots (dark red) in the spectrograms appear to be broader in frequency (range ~500-2000 Hz) and time and darker for the microphone adjacent to the barrier compared to the No Barrier site. The broadening also applies to the other lighter red parts of the spectrogram. For the community-side near positions, it is difficult to see any differences in the shapes or intensity of the hottest spots (dark red) in the spectrograms for the near positions. One observation is that the light blue appears to expand to lower frequencies for the site with No Barrier. For the community-side far positions, the dark red hotspots, in the range of about 500 Hz to 1,600 Hz, appear to be more filled in (a more distinct shape) with the barrier present. Figure 75 and Figure 76 show a heavy truck pass-by event at approximately 18:33 for the near- microphone community positions (Figure 75, Mics 3 and 5) and the far-microphone community positions (Figure 76, Mics 4 and 6). It was difficult to extract the events for Mics 1 and 2 (events were not distinguishable), so these are not shown. The truck is traveling northbound (barrier side of road), arriving first at the No Barrier site and then at the barrier site about 20 seconds later. For the community-side near positions, it is difficult to see any differences. One observation is that the light blue appears to expand to lower frequencies for the site with No Barrier. For the community-side far positions, it is difficult to see any differences. For one of the events, it appears the darkest red is a more distinguishable shape for the barrier site. In general, for the I-75 location, sound levels opposite the sound-absorbing noise barrier in some cases appear to be slightly higher than those with No Barrier at key frequencies, ones that contribute most to the overall noise level.

C-71 Figure 72. I-75 (sound-absorbing barrier) 5-minute spectrograms; top: BarRef01, bottom: NoBarRef02, start time 17:55.

C-72 Figure 73. I-75 (sound-absorbing barrier) 5-minute spectrograms; top: BarCom03, bottom: NoBarCom05, start time 17:55.

C-73 Figure 74. I-75 (sound-absorbing barrier) 5-minute spectrograms; top: BarCom04, bottom: NoBarCom06, start time 17:55.

C-74 Figure 75. I-75 (sound-absorbing barrier) heavy truck pass-by event at ~18:33 spectrograms; top: BarCom03, bottom: NoBarCom05.

C-75 Figure 76. I-75 (sound-absorbing barrier) heavy truck pass-by event at ~18:33 spectrograms; top: BarCom04, bottom: NoBarCom06.

C-76 For the I-70 sound-absorbing barrier location, spectrograms for a 5-minute data block are shown in Figure 77 through Figure 79. Figure 77 is for the barrier-side (reference) positions, Figure 78 is for the low-microphone community positions, and Figure 79 is for the high-microphone community positions. For the reference positions, it is difficult to see any differences in the shapes and shades of the hottest spots (dark red). For the community-side positions, it is difficult to see any differences in the shapes and shades of the hottest spots (dark red) in the spectrograms for both the low and high microphones. Figure 80 and Figure 81 show a single heavy truck pass-by event on I-70 at approximately 17:45. Figure 80 is for the low-microphone community positions, and Figure 81 is for the high-microphone community positions. The truck is traveling eastbound (opposite side of roadway from barrier), arriving first at the No Barrier site and second at the Barrier site approximately 32 seconds later. For the community- side positions, both low and high positions show that the hot spots are broader in frequency and possibly in time (seen for some of the microphone comparisons) with the barrier present. In addition, the hot test spots in some cases appear to be a darker red color for the microphones opposite the barrier compared to the comparable microphones at the No Barrier site, again from approximately 500 to 2,000 Hz. In general, for the I-70 location, sound levels opposite the absorptive noise barrier appear to be slightly higher than those with No Barrier at key frequencies, ones that contribute most to the overall noise level.

C-77 Figure 77. I-70 (sound-absorbing barrier) 5-minute spectrograms; top: BarRef01, bottom: NoBarRef02, start time 15:30.

C-78 Figure 78. I-70 (sound-absorbing barrier) 5-minute spectrograms; top: BarCom03, bottom: NoBarCom05, start time 15:30.

C-79 Figure 79. I-70 (sound-absorbing barrier) 5-minute spectrograms; top: BarCom04, bottom: NoBarCom06, start time 15:30.

C-80 Figure 80. I-70 (sound-absorbing barrier) heavy truck pass-by event at ~17:45 spectrograms; top: BarCom03, bottom: NoBarCom05.

C-81 Figure 81. I-70 (sound-absorbing barrier) heavy truck pass-by event at ~17:45 spectrograms; top: BarCom04, bottom: NoBarCom06.

C-82 C H A P T E R C - 9 Difference Spectrograms and Comb Filtering This portion of the comparison of the Phase 1 and Phase 2 results focuses on spectrogram differences. Key elements of the comparison are: The research team developed a method to visualize spectrogram differences for the same vehicle passing by a Barrier site and an equivalent No Barrier site. Spectrogram difference analysis revealed harmonically related peaks caused by comb filtering (direct and barrier-reflected sound waves combine, with constructive and destructive interference, resulting in comb filtering). Comb-filtered sound can be perceived as buzzy or raspy. Absorptive barriers may reduce the comb filtering effect, although this would need to be substantiated by conducting a narrow-band analysis. Spectrograms were generated for both sound-reflecting noise barriers and sound-absorbing noise barriers. For each barrier type, examination of isolated vehicle pass-by events helped to compare spectral content between sound levels measured at the barrier site and measured at the No Barrier site. Some differences are apparent when examining the two spectrograms (Barrier and No Barrier); however, subtle differences cannot always be seen. Identifying subtle differences is key to comparing sound-reflecting and sound-absorbing barriers. To accomplish this, a method was developed to readily visualize subtle differences. The method results in difference spectrograms, which can then be compared for sound- reflecting barriers and sound-absorbing barriers. The spectrogram comparison method uses spectral data from the same vehicle passing through the Barrier site and the No Barrier site. The maximum sound level at each site is aligned after applying 3-second averaging to the data. Once the maxima are aligned for the event from each site, 1-second averaging is applied, and differences for each one-third octave band are used to create a difference spectrogram (Barrier minus No Barrier). The averaging times were optimized to expose key spectral features (to expose distinctive horizontal lines of high amplitude, described more later). A positive difference (Barrier louder than No Barrier) is indicated with increasing intensity of red, and a negative difference (Barrier quieter than No Barrier) is indicated with increasing intensity of blue. White indicates no difference in sound level between the Barrier and No Barrier sites. The difference spectrograms were created for both the reflective and absorptive barriers for single vehicle pass-by events. The results for the reflective barriers are shown first, followed by results for the absorptive barriers, concluding with a comparison of the results for the two barrier types. For the reflective barriers, six clean vehicle pass-by events were extracted, two each for sites MD-5, I-90, and SR-71. Figure 82 through Figure 93 are pairs of figures for each event. The first figure of each pair shows: 1) the overall A-weighted sound level time history for each event at each site (top graph); 2) the spectrograms at the Barrier and No Barrier sites (middle two plots); and 3) the difference plot (bottom) for each event. The

C-83 second figure of each pair is a plot showing a slice in time that reveals the peaks in differences by one-third octave band frequency. Examination of the spectrogram difference plots reveals lines of hot spots across the spectrograms, particularly just before and after the maximum sound level of the event. The slice-in-time plots show the location of the “hot lines,” revealing multiple peak frequencies with a special relationship. (The time chosen for each slice was based on visual distinction of high-amplitude horizontal lines in the related spectrogram difference plot and to be most representative of high-amplitude lines before and after the vehicle passes by (the closest point of approach typically does not reveal the lines).) In all six pass-by examples, the peak difference frequencies are harmonically related, with few exceptions. Table 8 lists the peak difference frequencies for each event, with a comment about the harmonic relationships. For a harmonic relationship, the frequency must be a multiple of the base frequency; for example, for a base frequency of 25, harmonically related frequencies are 50, 75, 100, 125, etc., which are the base times 2, 3, 4, 5, etc., respectively. Research into reasons why the barrier sites would have higher sound levels in these harmonically related frequencies revealed comb filtering as a cause. (Note that the exceptions to the harmonic relationships are harmonically related to each other when there is more than one; this could indicate there are reflection effects from another surface, such as the roadway pavement.) Table 8. Peak difference frequencies for sound-reflecting barriers. Site and Event Peak Difference Frequencies (Hz) Harmonic Relationships MD-5 19:46 16, 20, 40, 80, 160, 400, 800, 1,600, 12,500 All except 16 are related to 20 Alternatively, all except 20 and 40 are related to 16 MD-5 20:09 25, 50, 100, 200, 400, 1,000, 1,600, 6,300, 10,000 All are related to 25 I-90 14:41 16, 25, 31.5, 50, 63, 125, 250, 500, 1,000, 2,000, 3,150, 5,000, 8,000 All except 16, 31.5, and 63 are related to 25 I-90 16:17 16, 25, 50, 63, 100, 250, 500, 2,500 All except 16 and 63 are related to 25 SR-71 10:44 25, 50, 80, 315, 400, 630, 800, 2,000, 2,500, 6,300, 8,000, 12,500 All except 80, 315, and 630 are related to 25 SR-71 12:10 25, 50, 80, 400, 1,250, 2,500 All except 80 are related to 25 Comb filtering is an effect created by a direct-path sound wave combining with a reflected-path sound wave, where the reflected-path sound is delayed in time from the direct path. The combination results in harmonically related peaks in the received sound spectral content, where there is constructive interference of the two sound waves (for frequencies that arrive in phase, there is constructive interference; for frequencies that arrive out of phase, there is destructive interference). Harmonically related peaks can result in perception of tonality. In audio engineering, the comb filtering effect is described as sounding metallic, boxy, or artificial, and can make higher frequencies sound odd or harsh. Since these descriptions are about recording studios, where reflecting walls are close by, the delay between direct and reflected waves is quite small (i.e., a few milliseconds [ms]). In psychoacoustics, comb filtering is discussed in terms of coloration of sound caused by a single reflection (Johansen 2006). The effect depends on the delay time of the reflected sound. Humans are particularly sensitive to coloration caused by delays of about 5 ms. Coloration can be regarded as a frequency domain effect (a change in timbre) for delay times up to approximately 25 ms. If the delay time exceeds 25 ms, the perception changes from coloration to a rough character effect, where the regular repetition is detected as a time domain effect. Further psychoacoustic evaluation describes “repetition pitch.” Signals consisting of a sound, together with a repetition of that sound after a delay time , can evoke well-defined pitch sensations corresponding to 1/ (Bilsen and Ritsma 1970). For example, if you have a

C-84 delay of 10 ms, this corresponds to a repetition pitch of 1/0.010 = 100 Hz. Longer delay times result in lower-frequency repetition pitches. If the delay is too long, it would be perceived as an echo. The delay times associated with typical highway geometries could range from about 8 to 200 ms, depending on the number of travel lanes, median width, barrier placement, and placement of the vehicle (upstream or downstream). At the time of maximum sound level, the time delay is greater than when vehicles are upstream or downstream. For a single vehicle passing by, it is possible to perceive comb filtering effects as the vehicle approaches, likely more of an echo or fuller sound at the closest point of approach. To help understand the effects, the audio file for a vehicle pass-by event at a No Barrier site was delayed in time and added to the original event to simulate the barrier effect. The delay times ranged from 20 ms to 200 ms. For the 20 ms delay, the effect was an obvious raspiness or buzziness, and that effect decreased as the delay time increased. A test was also done with a sweeping time delay, starting at 20 ms upstream, increasing to 100 ms at the closest point of approach, and decreasing to 20 ms downstream. The result is as expected: raspiness or buzziness that decreases as the vehicle approaches, a full sound at the closest point of approach, and increasing raspiness or buzziness as the vehicle recedes. These time-delayed audio files were then subjected to a spectrogram analysis. For the analysis, the sound levels between Barrier and No Barrier cases were not adjusted; the only effect applied is the time offset. Figure 94 shows the difference plot for the sweeping time delay, which simulates a real pass-by event (although the time delays do not exactly match those that would apply to the MD-5 19:46 event). The difference plot exposes the lines of hot spots as was seen for the actual comparisons for measured data at the reflective Barrier and No Barrier sites. The spectrum at a slice in time (Figure 95) shows peak difference frequencies at 12.5 Hz, 20 Hz, 63 Hz, 100 Hz, 200 Hz, 500 Hz, 800 Hz, 1,250 Hz, and 12,500 Hz. All the frequencies are harmonically related to 12.5 Hz, except 20 Hz. In summary, adding a sweeping time delay to a pass-by event and combining it with the original event simulates the barrier reflection effects, and this results in the comb filter effect. So, what does this all mean for highway noise barrier reflections? 1. As was previously observed, the overall sound levels are increased slightly near the road and up to a few decibels farther from the road. Also, some frequencies are enhanced more than others, particularly in the low- to mid-frequency range (generally below 1 kHz). 2. In addition to an increase in sound levels, comb filtering effects are adding tonal qualities to received sound, particularly in low to mid frequencies. These additions would apply to both near and far distances from the road. This may change the sound quality by adding a raspiness or buzziness to the sound, particularly as a vehicle is approaching or receding. 3. The delay times associated with reflected sounds with the sites measured are about 8 to 200 ms, which may result in very low-frequency repetition pitches (5 Hz to 125 Hz). These frequencies and their harmonics create a comb filter effect that is dependent on each site’s geometry. While it is typically described that the audible range for humans is 20 Hz to 20,000 Hz, for very low frequencies (below 20 Hz, or infrasound), the sound may be slightly audible or perceived as vibrations in various parts of the body. It is possible that very low frequencies enhanced by the presence of a barrier may be contributing to the objectionableness of the sound. However, the low frequencies are only in the 30 dBA to 40 dBA range, so tonal enhancements at these low levels may go unnoticed. Understanding possible low-frequency effects would require further investigation.

C-85 Figure 82. Spectrogram difference plot for MD-5 (sound-reflecting barrier) diesel pickup with trailer ~19:46; BarCom04 and NoBarCom06.

C-86 Figure 83. Differences at time -2 seconds from maximum; MD-5 (sound-reflecting barrier) diesel pickup with trailer ~19:46; BarCom04 and NoBarCom06.

C-87 Figure 84. Spectrogram difference plot for MD-5 (sound-reflecting barrier) pickup ~20:09; BarCom04 and NoBarCom06.

C-88 Figure 85. Differences at time -0.5 seconds from maximum; MD-5 (sound-reflecting barrier) pickup ~20:09; BarCom04 and NoBarCom06.

C-89 Figure 86. Spectrogram difference plot for I-90 (sound-reflecting barrier) heavy truck ~14:41; BarCom04 and NoBarCom06.

C-90 Figure 87. Differences at time +2.7 seconds from maximum; I-90 (sound-reflecting barrier) heavy truck ~14:41; BarCom04 and NoBarCom06.

C-91 Figure 88. Spectrogram difference plot for I-90 (sound-reflecting barrier) heavy truck ~16:17; BarCom04 and NoBarCom06.

C-92 Figure 89. Differences at time +1.75 seconds from maximum; I-90 (sound-reflecting barrier) heavy truck ~16:17; BarCom04 and NoBarCom06.

C-93 Figure 90. Spectrogram difference plot for SR-71 (sound-reflecting barrier) heavy truck ~10:44; BarCom04 and NoBarCom06.

C-94 Figure 91. Differences at time +1.5 seconds from maximum; SR-71 (sound-reflecting barrier) heavy truck ~10:44; BarCom04 and NoBarCom06.

C-95 Figure 92. Spectrogram difference plot for SR-71 (sound-reflecting barrier) motorcycle ~12:10; BarCom04 and NoBarCom06.

C-96 Figure 93. Differences at time +1.1 seconds from maximum; SR-71 (sound-reflecting barrier) motorcycle ~12:10; BarCom04 and NoBarCom06.

C-97 Figure 94. Spectrogram difference plot for MD-5 (sound-reflecting barrier) diesel pickup with trailer ~19:46; simulated barrier site and NoBarCom06.

C-98 Figure 95. Differences at time -3 seconds from maximum; MD-5 (sound-reflecting barrier) diesel pickup with trailer ~19:46; simulated barrier site and NoBarCom06. The difference spectrograms were also created for the I-75 and I-70 sound-absorbing barriers. Both barriers used the same sound-absorbing product, and results could vary by product because of differences in the one-third octave band absorption coefficients. For these sound-absorbing barriers, four clean vehicle pass-by events were extracted, two each for the I-75 and I-70 locations. Figure 96 through Figure 103 show the difference plots for each event; darker red was applied to the color scale for the absorptive sites to properly show lines since differences in spectrograms are subtler for absorptive barriers than for reflective barriers. After each difference plot, a plot showing a slice in time reveals the peaks in differences. (Difference spectrograms for I-270 were not created due to the interference from reflected noise from homes behind the No Barrier microphone.) As with the sound-reflecting barriers, examination of the spectrogram difference plots for the sound- absorbing barriers reveals “hot lines” with special relationships. Table 9 lists the peak difference frequencies for each event, with a comment about the harmonic relationships. Unlike the sound-reflecting barrier lines, the sound-absorbing barrier lines have many exceptions to a harmonic relationship to a single base frequency. (Similar to the sound-reflecting barriers, the exceptions have harmonic relationships, although not all to the same base frequency.) For both barrier types (although occurring more for sound- absorbing barriers), there are instances of adjacent one-third octave bands together representing a peak.

C-99 This could indicate that a twelfth-octave narrow-band analysis, or possibly an even narrower band analysis (showing all frequency content), is needed to reveal what is truly happening on a frequency basis. The following possibilities may influence the peaks (and dips): 1) there are peak frequencies between two one- third octave bands, 2) each one-third octave band has distinct peaks, or 3) there is broadband energy including and between the two peaks. Particularly in the high frequencies, which have larger bandwidths (include a larger range of frequencies) than lower frequencies, visualization of peaks/dips may be lost without narrow-band analysis. To help determine if there are any trends when comparing the two barrier types, all the spectral slice-in- time plots for both the sound-reflecting and sound-absorbing barrier sites are presented in a single plot (Figure 104). The combined plot shows that reflective barrier peaks/dips are pronounced and show a strong harmonic relationship for lower frequencies (500 Hz and lower), as compared to sound-absorbing barrier peaks/dips. In addition, the sound-absorbing barrier lines are generally lower amplitude (smaller differences between Barrier site and No Barrier site) than the sound-reflecting barrier lines for the lower-frequency range. If narrow-band analysis were to reveal nothing more than what is currently seen with the one-third octave band data, one could assume that sound-absorbing barrier surfaces affect the reflected sound by reducing the comb filtering effect. This cannot be substantiated, however, until narrow-band analysis is applied (which was beyond the scope of this study). Table 9. Peak difference frequencies for sound-absorbing barriers. Site and Event Peak Difference Frequencies (Hz) Harmonic Relationships I-75 18:18 16, 31.5, 50, 80, 200, 400, 630, 1,250, 4,000, 6,300, 12,500 All except 16, 31.5, 80 and 630 are related to 50 All except 50 and 200 are related to 16 I-75 18:33 20, 31.5, 63, 80, 160, 315, 400, 1,000, 2,000, 3,150, 6,300, 10,000 All except 20, 80, 160, 400, 1,000, 2,500, and 10,000 are related to 31.5 All except 31.5, 63, 315, and 3,150 are related to 20 I-70 17:44 12.5, 20, 25, 100, 160, 250, 315, 630, 1,000, 2,500, 4,000, 5,000, 6,300, 10,000 All except 12.5, 25, 250, 315, and 630 are related to 20 All except 20, 315, and 630 are related to 12.5 I-70 17:50 12.5, 20, 31.5, 50, 63, 100, 200, 630, 1,000, 2,500, 4,000, 6,300, 8,000, 12,500 All except 12.5, 31.5, 50, 63, and 630 are related to 20 All except 20, 31.5, 63, and 630 are related to 12.5

C-100 Figure 96. Spectrogram difference plot for I-75 (sound-absorbing barrier) heavy truck ~18:18; BarCom04 and NoBarCom06.

C-101 Figure 97. Differences at time 2.5 seconds from maximum; I-75 (sound-absorbing barrier)) heavy truck ~18:18; BarCom04 and NoBarCom06.

C-102 Figure 98. Spectrogram difference plot for I-75 (sound-absorbing barrier) heavy truck ~18:33; BarCom04 and NoBarCom06.

C-103 Figure 99. Differences at time -0.25 seconds from maximum; I-75 (sound-absorbing barrier) heavy truck ~18:33; BarCom04 and NoBarCom06.

C-104 Figure 100. Spectrogram difference plot for I-70 (sound-absorbing barrier) heavy truck ~1744; BarCom04 and NoBarCom06.

C-105 Figure 101. Differences at time -0.75 seconds from maximum; I-70 (sound-absorbing barrier) heavy truck ~17:44; BarCom04 and NoBarCom06.

C-106 Figure 102. Spectrogram difference plot for I-70 (sound-absorbing barrier) heavy truck ~17:50; BarCom04 and NoBarCom06.

C-107 Figure 103. Differences at time -2 seconds from maximum; I-70 (sound-absorbing barrier) heavy truck ~17:50; BarCom04 and NoBarCom06.

C-108 Figure 104. Spectral difference plots for vehicle pass-by events for all sound-reflecting and sound- absorbing barrier sites.

C-109 R E F E R E N C E S Frans A. Bilsen and Roelof J. Ritsma, “Some Parameters Influencing the Perceptibility of Pitch,” Journal of the Acoustical Society of America, Volume 47, Number 2 (Part 2), 1970. Lars G. Johansen, “Psychoacoustics and Audibility – Fundamental Aspects of the Human Hearing,” Lecture notes for the course TI-EAKU, University College of Aarhus, 2006.

D-1 Using the Barrier Reflections Screening Tool A P P E N D I X D Judy Rochat and Keith Yoerg ATS ConSulTing Pasadena, CA

D-2 CONTENTS CHAPTER D-1 .................................................................................................................................... D-3 Intended Use ......................................................................................................................................................... D-3 CHAPTER D-2 .................................................................................................................................... D-4 Instructions for Use ............................................................................................................................................... D-4 CHAPTER D-3 .................................................................................................................................... D-5 Validation of Estimates ......................................................................................................................................... D-5

Next: Appendix D - Using the Barrier Reflections Screening Tool »
Field Evaluation of Reflected Noise from a Single Noise Barrier Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 886: Field Evaluation of Reflected Noise from a Single Noise Barrier analyzes the characteristics of sound reflected from a noise barrier to the opposite side of a highway. State departments of transportation (DOTs) periodically receive complaints from residents about increases in traffic noise that residents believe are the result of noise reflected from a new noise barrier added across the roadway from them. Currently available analytical tools are limited in their ability to evaluate reflected noise and some of the subtle changes in the quality of sound that can occur when it is reflected. Therefore, it is a challenge for DOTs to determine conclusively if complaints about reflected noise are the result of actual or perceived changes in noise characteristics, and to identify locations where absorptive surface treatments could be beneficial.

The study compares reflected noise from sound-reflecting barriers and from barriers with a sound-absorptive surface. It examines both the levels and frequencies of reflected noise to better understand how reflected noise is experienced by communities.

The full report, which includes four detailed appendices, is 27 MB and may take time to download. It is accompanied by several appendices, a tool, and a guide:

A presentation file that summarizes the research also is available on the report project page.

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