NOISE MITIGATION - BARRIER To mitigate noise in exterior recreation areas: ＞ Rearrange site (potentially provides both distance and barriers) ＞ Put up a noise-specific barrier If there are existing barriers such as buildings or topographic features between project site and noise source, first evaluate whether they provide sufficient mitigation Mitigation should be in direction of main noise source(s)

NOISE MITIGATION - BARRIER To be effective, barrier must: ＞ Interrupt line of sight between noise source and receptor ＞ Be continuous, and extend to the ground surface ＞ Be of a material that will absorb sound energy When considering wooden fences as barriers, incorporate an air space between two continuous fence surfaces to increase effectiveness Noise Guidebook has Transmission Loss Values for evaluating the relative effectiveness of various materials

NOISE MITIGATION - BARRIER

To evaluate barrier, need to know: ＞ Observer elevation ＞ Noise source elevation ＞ Current and projected noise levels ＞ Elevation of the top of the barrier ＞ Distance, observer to barrier ＞ Distance, barrier to source ＞ Angle subtended by barrier

NOISE MITIGATION - BARRIER Sample site: ＞ Observer elevation: 525 ft ＞ Source elevation: 514 ft ＞ Current noise level: dB ＞ Projected noise level: dB ＞ Barrier top elevation: 546 dB ＞ Observer-barrier distance: 141 ft ＞ Barrier-source distance: 523 ft ＞ Barrier angle: 95 degrees

NOISE MITIGATION - BARRIER Follow calculations in Noise Guidebook Workchart 5

NOISE MITIGATION - BARRIER Refer to Workchart 6 and Workchart 7 in guidebook as directed by Workchart 5 to complete evaluation

NOISE MITIGATION - BARRIER To improve barrier performance without changing dimensions: ＞ Move closer to observer – increases effective angle of barrier ＞ Angle ends toward observer – also increases effective angle ＞ Angle top toward source – increases effective height of barrier

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