Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts (2022) / Chapter Skim
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1 Introduction National Cooperative Highway Research Program (NCHRP) Project 25-57: "Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts" examined strategies other than traditional noise barriers to reduce highway traffic noise.
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2 Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts Strategy Noise Benefit Costs (scale $–$$$$$) Context Appropriateness On-Road Design Strategies Quieter bridge decks and joints: - Quieter bridge decks using diamond grinding or polyester overlays 5 to 10 dB (near source)
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Summary 3 Solid safety barrier in lieu of guardrail: - For freeway/highway Preliminary investigations: 0.4 dB to 2.6 dB depending on project specifics: distance to receiver and site topography Further investigations: at 100 ft, 5 to 7 dB reduction, up to 8 dB with road slightly elevated (assumes tall freeway/highway safety barrier, 6.8 ft) ; best for hard ground sites and low % heavy trucks (% HTs)
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4 Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts Right-of-Way Design Strategies Low-height berms: - Standard low-height berms (up to 6 ft high) The noise benefit of low-height berms ranges from 2 dB to more than 10 dB.
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Summary 5 Vegetated screens: - Thick vegetation belts (65 ft) Measured noise reduction of 3 to 9 dB; up to 10 dB noise reduction in computational model with optimized planting ($–$$$)
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6 Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts Sound-absorbing ground surface and ground treatment: - Acoustically soft ground TNM predictions show 1 to 2 dB for placement in ROW or median, however, more may be realized with gravel surfaces (multi-lane highway)
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Summary 7 Solar panels If continuous panels assumed, then > 11 dB; however, gaps between arrays and panel angles need to be considered.
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8 Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts Sound-absorptive treatment: - Treatment on retaining walls Opposite side reflection: 1 to 2 dB with changes in spectral content potentially reducing adverse reflected noise effect Parallel barriers: predicted up to 2.5 dB Truck/barrier wall reflections: predicted up to 4 dB ($$–$$$) Varies by treatment/project (one example was $18–$22/ft2)
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Summary 9 More details of the three further investigations are summarized as follows. Low berms were examined in terms of berm height, width, placement, shape, top width, and berm surface ground type.
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10 Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts Acoustically soft ground strips were examined in terms of strip width and sound absorption value. The strips were also combined with quieter pavement to help reduce highway traffic noise.
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