IMPACTS RELATED TO PAVEMENT TEXTURE SELECTION
Kuemmel, DA;Jaeckel, JR;Satanovsky, A;Shober, SF;Schmiedlin, RB
Abstract
In the early 1990s, the impacts of pavement noise in urban areas were gaining both state and national attention. The Wisconsin Department of Transportation (WisDOT) decided to take a proactive approach to investigate both asphaltic concrete (AC) and Portland cement concrete (PCC) pavement textures that would result in the lowest exterior noise levels. At the same time, safety of the traveling public had to be assured. Consequently, a research work plan was developed by industry and WisDOT, with Marquette University contracted as the principal investigator. Later, Minnesota DOT (MinnDOT) joined in the research effort when modifications were made to the work plan to include interior (inside the vehicle) noise levels. Twelve PCC pavements were constructed in 1994, with various tine spacings at various depths to compare to WisDOT's standard 25 mm (1 in.) tine spacing and 3 mm (1/8 in.) depth. Four AC pavements were also evaluated (a coarse and a fine SMA mix and a Superpave mix) and compared to WisDOT's standard dense-graded AC mix. The factors evaluated by this research included: exterior noise measurements (including subjective comparisons); friction properties; texture depths; and other related characteristics (such as influences on tire spray and winter maintenance). As the study progressed, interior noise evaluation became a mutually desirable part of the study for WisDOT and MinnDOT. This study has resulted in several significant findings of interest to highway users. Uniformly spaced tines produce a noise with a prominent discrete tone commonly referred to as "whine"; a truly random tine spacing does not produce such a tone. Asphalt pavements, and PCC pavements with longitudinal tining, broom, turf drag and Skidabrader finishes do not produce an audible whine (however, turf drag or broom finishes have lower frictional properties). For cars, SMA surfaces have some acoustical advantage over standard AC surfaces, but only at frequencies higher than 2000 hz. The objectionable whine of many PCC textures is poorly related to overall exterior or interior noise levels (dBA). Narrow band frequency analysis does identify prominent discrete tones that correlate to the presence of a whine. PCC pavements can be produced that have acoustically favorable characteristics without compromising safety; these include a truly random tine spacing, skewed tining, longitudinal tining and a Skidabrader treatment. This study concludes that it is possible (very simply and at no extra expense) to build a PCC pavement that does not "whine" and has the desired frictional properties. Such a pavement is a "good neighbor", is safe, provides user comfort, and is durable.