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Reflective and non-reflective Highway Barriers. K. Polcak (MD SHA) And R.J. Peppin (Scantek, Inc.). TRB ADC 40 Summer Meeting, 2010, Denver, CO. Reflections of Noise and Highway Barriers. What source to use? Point? Multiple point? Line? What road type to use? Straight? Curved?
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Reflective and non-reflective Highway Barriers K. Polcak (MD SHA) And R.J. Peppin (Scantek, Inc.) TRB ADC 40 Summer Meeting, 2010, Denver, CO
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?
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
Line Source-Section Absorptive Reflective
Two 5m Barriers Reflective Absorptive
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
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