Hot-mix Asphalt Placement: Virginia's Move to a Two-inch Drop-off

About the report:

In 2004, the Virginia Department of Transportation (VDOT) began examining the effects of allowing a 2-inch drop-off, rather than the specified 1.5-inch drop-off, between adjacent lanes. VDOT implemented a pilot program in its Northern Virginia District that gave paving contractors the option of not squaring up at the end of each shift on limited access roadways. This type of operation allowed the contractor to leave a milled section open to the traveling public and also to place an overlay in one lane but not the adjacent lane. The maximum allowable drop-off of the pavement in these instances was 2 inches. The purpose of this study was twofold. The first was to develop a functional performance specification for the milled surface exposed to traffic during paving operations on limited access roadways. This was done by measuring the milled surfaces on the roadways in the VDOT pilot program. The practices of other states regarding edge drop-offs were also investigated. The second and more important purpose was to investigate specific factors affecting paving and milling operations: safety, quality, productivity, and efficiency. The safety issues addressed included the effects of drop-offs created by milling or a straight overlay, loose debris created by raveling and "scabbing," windshield damage and accidents, and lane closure exposure time of the milling and paving crews. The condition of the milled surface was investigated to determine quality. To determine productivity and efficiency, three operations were investigated and compared: performance planing, mill and fill, and straight overlays. These investigations were conducted on particular limited access roadways in VDOT's Northern Virginia, Fredericksburg, and Salem districts. The results were as follows: 1.) The sand patch test was adopted to calculate the mean texture depth of milled surfaces, and a maximum average mean texture depth of 2 millimeters was validated for milled surfaces exposed to traffic on limited access roadways. 2.) The use of a 2-inch milling depth, as well as the use of the micro-milling operation, helps reduce scabbing. A 2-inch drop-off also works well. 3.) Performance planing increases paving production by 32 percent and milling production by 49 percent over those of mill and fill. By using a performance planing operation, rather than a mill and fill operation, VDOT could save $103,500 per year in traffic control costs and $522,000 per year in labor and equipment costs. Further, the use of performance planning would reduce both the exposure time of paving and milling workers to lane closures and user delays.

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