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Effects of Reflective and Non-Reflective Highway Barriers on Noise Reflections

Explore the impact of different barriers on noise reflection in highway settings, including sources to use, road types, and absorption coefficients. Assumptions based on common barrier equations and barrier surface absorption variations are considered. Various barrier setups are analyzed, comparing reflective and absorptive barriers on straight and curved roads. Results show the sensitivity of sound absorption coefficients on barrier effectiveness, emphasizing the need for larger barriers to reflect low frequencies. Tentative conclusions suggest the benefits of absorptive barriers and caution against solely relying on reflective barriers, especially in curved road sections and near multi-story buildings. Further studies are recommended before implementing reflective barriers.

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Effects of Reflective and Non-Reflective Highway Barriers on Noise Reflections

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  1. Reflective and non-reflective Highway Barriers K. Polcak (MD SHA) And R.J. Peppin (Scantek, Inc.) TRB ADC 40 Summer Meeting, 2010, Denver, CO

  2. Reflections of Noise and Highway Barriers • What source to use? • Point? • Multiple point? • Line? • What road type to use? • Straight? • Curved? • What frequency to use? • What absorption coefficient to use?

  3. Assumptions • ISO 9613-2 propagation • Propagation of point sources • Line sources are represented by point sources appropriately spaced • Common barrier attenuation equation • Surface absorption of barriers from 0.0 to 1.0 • Up to two orders of reflection • Source 1-m above ground • Receiver 1.5-m above ground • Soft ground

  4. Basic Set-up

  5. No Barrier

  6. No Barrier

  7. 3m Barrier ά=1.0

  8. 5m Barrier ά=1.0

  9. 5m Barrier ά=1.0

  10. 10m and 10m Barriers ά=1.0

  11. 10m, 10m Barrier ά=1.0

  12. 10m, 10m Barrier ά=1.0, 0.0

  13. Higher Barrier is Absorping

  14. 10m, 3m Barrier ά=0.0, 1.0

  15. Higher Barrier is Reflecting

  16. 10m, 10m Barrier ά=0.0, 1.0

  17. 10m 3m Barrier Reflecting

  18. 10m 3m Barrier Reflecting

  19. 10m, 10m Barrier, Both Reflecting

  20. 10m, 10m Barrier, Both Reflecting

  21. 10m, 10m Barrier, Both Reflecting

  22. Reflective Barrier as Seen on Road

  23. Left- Blue =55 Right Last Blue = 55

  24. Several Point Sources 10m Apart

  25. Multi Sources Spread Sound

  26. No Barriers

  27. Line source

  28. No Barrier

  29. Line Source-Section Absorptive Reflective

  30. Improvement over No-barrier

  31. Curved road

  32. No Barriers

  33. Two 5m Barriers Reflective Absorptive

  34. Usefulness of Barriers on Curved Sections

  35. Sound Absorption sensitivity

  36. Sensitivity- NOT DEFINITIVE • Only calculated for 500 Hz • Trends should be good • Results dependent not only on sound absorption coefficient, ά, but also on size of barrier • High sound absorption coefficients at low frequency for low barriers don’t really make sense. • You need big barriers to reflect low frequencies

  37. A 5m BarrierAbout 1 dB difference from 0.0 to 1.0

  38. Some Tentative Conclusions • Better to have a barrier than not- most times • Better to have absorptive than not! • Reflective might be worse than nothing in some instances. • Curves • Residents in multi-story buildings • Differences in sound absorption coefficient of less than perhaps 0.3 is worth squat. • Before putting in reflective barriers do a study to see if it makes sense

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