According to a study funded by the National Cooperative Highway Research Program, initial pavement smoothness significantly affects future pavement smoothness, leading to pavements that remain smoother longer. But what's the best way to get better initial smoothness so that pavements last longer before requiring rehabilitation because of unacceptable ride quality?

The Missouri Department of Transportation has tested one approach that produced a section of experimental pavement with a ride so smooth it's been dubbed the "white velvet" section. The secret weapon used to achieve this result: A diamond grinding machine, not just for bump cutting, but for the entire 24-foot-wide driving surface. The experimental project was a 4½ -mile-long section of Missouri Route 60 east of Poplar Bluff. Total width of the 12-inch-thick, nonreinforced pavement, including shoulders, was 38 feet, with doweled joints spaced at 15 feet. However, only the two 12-foot travel lanes were diamond ground. For comparison purposes, MoDOT had the same paving contractor for the experimental section build an adjacent 6-mile-long concrete pavement section that required the normal construction procedure, including tining. This pavement section also was 38 feet wide and 12 inches thick. Grinding results for the experimental section were outstanding. The average profile index for the whole section, measured with a zero blanking band, was 6.8 inches, with one day's production at 5 inches. The adjacent tined job had indexes in the 10- to 20-inch range, also measured with a zero blanking band.