That loud and obnoxious "whine" or "hum" produced when a car drives over grooved or "tined" concrete pavement has met its match. Artificial grass--also known as AstroTurf--is often used as the groundcover for putt-putt golf and some football fields. In Minnesota, however, it's doing more than padding athletic pursuits; it's quieting highways.
Astroturf has been used for years on low-volume roads. But a new approach weights the wiry plastic grass down with gravel and drags it over freshly poured concrete. The rough surface that follows this treatment is pocked so that it is skid-resistant--something tining is supposed to provide--but it also eliminates the high-pitched whine of cars traveling over grooved pavement.
"It looks a lot like the concrete sidewalks that have that broom-like indentations," says David Rettner, a former concrete research engineer at Minnesota's Department of Transportation who teamed with officials from Wisconsin's DOT in the research effort to solve the noise problem.
The Federal Highway Administration still recommends tining for all concrete bridges based on a study conducted in the 1970s by the Texas DOT which found that wet-weather accidents were greatly reduced when tining was applied to bridge decks. The new texture is just as safe as the tining, says MnDOT's Pavement Engineer Curt Turgeon. "We've been looking at accident reports and haven't seen any change."
The FHWA gave Minnesota permission to replace tining with the new AstroTurf texture.