Absorptive Sound Barriers: Effects of Three Potential Changes to Current Design Standards of Virginia Department of Transportation

Abstract

The Virginia Department of Transportation (VDOT) currently designs absorptive sound barriers with their entire face absorptive [noise reduction coefficient (NRC) of 0.8 or greater]. Using the FHWA Traffic Noise Model, the sound level increases caused by three modifications to current VDOT practice were investigated: a more reflective barrier surface (NRC = 0.7), a 6-in. (15-cm) reflective cap, and a 2-ft (61-cm) reflective base. These increases were computed for receivers up to 40 ft (12.2 m) above the ground and 1,000 ft (305 m) behind the barrier. The computations included three barrier locations—barrier opposite receivers, barrier same side as receivers, and barriers on both sides—at several barrier heights and distances from the roadway. They also included two roadway widths and two traffic conditions, to span the extreme ranges of these variables. Results indicate that for a barrier opposite the receivers, the more reflective surface caused a maximum increase of 1.3 dB, the 2-ft (61-cm) reflective base caused a maximum increase of 1.7 dB, and all three modifications combined inflated this increase to 2.7 dB. For a barrier on the same side of the roadway as the receivers, no situations caused increases greater than 1 dB. Finally, for barriers on both sides of the roadway, the more reflective surface caused a maximum increase of 1.1 dB, and all three modifications combined inflated this increase to 1.5 dB. A table of resulting sound level increases for the full field of computed receivers—for the worst-case situations encountered in the computations—is included.