OBSI Tests on Thin Overlay Mixes in Austin, Texas

The Austin District of the Texas Department of Transportation in the United States has implemented the use of Thin Overlay Mixes as pavement surfaces for the purpose of reducing traffic noise. Such overlays are non-structural hot-mix asphalt mixes that are typically placed in thin lifts of about 2.5-cm thick. Commonly, these applications are part of a pavement preservation program to address surface distresses such as raveling, aging, bleeding, minor cracking, texture loss, etc. However, the Austin District has recently experimented with the placement of several of these overlays solely for the purpose of mitigating noise generated at the tire-pavement interface with excellent results, both on low-volume roads and major highways. The benefits include lower noise levels perceived at adjacent neighborhoods that had been affected by highway noise, as well as lower noise levels perceived by the driving public, by reducing the annoyance inflicted to the drivers inside the vehicle. This investigation has conducted on-board sound intensity tests on these pavements in and around the vicinity of Austin, Texas, for approximately four years, finding significant noise level reductions when compared to conventional pavements as well as to other quieter pavements, i.e., permeable friction courses (open-graded asphalt concrete).