Double Drum Vibratory Breakdown Rollers

Purpose of this compaction process 

Perhaps the most efficient method to compact a tender mix within the upper temperature range is to use two DDV rollers in echelon (almost side by side).One DDV roller can operate on one side of the mat and the other DDV roller can operate on the other side of the mat. In essence, when one roller moves toward the paver on one side of the lane, the other roller also moves toward the paver at the same time on the other side of the same lane. The rollers operate together, moving forward and backward at the same time on different portions of the mat. The purpose of this compaction process is to get as much density in the mat as possible before the temperature of the mix drops into the middle or tender temperature range and the mix begins to shove and move under the steel wheel rollers. 
Equipment Exhibition
Drum Vibratory Breakdown Rollers
The exact roller pattern used depends on many factors. Some of those factors include the width of each DDV roller used, the width of the lane being placed, the temperature of the mix immediately behind the paver screed, the temperature at which the mix starts to move and shove (the start of the tender zone), and the maximum frequency at which each vibratory roller can operate. Ideally, the two DDV rollers should be of the same make, model, and condition. This will assure that the compactive effort applied to the mat is equal across the width of the lane. 
In order to adequately compact an asphalt concrete mixture, it is proper to extend the edge of the vibratory or static steel wheel roller drum over the unsupported edge of pavement and/or over the longitudinal joint by at least 150 mm (6 in.). Theoretically, therefore, one would need a 3.9 m (13 ft) wide roller to compact a 3.66 m (12 ft) wide pavement, allowing for a 150 mm (6 in.) overlap of the outside edges, whether unsupported or a longitudinal joint. Since no roller exists that is 3.96 m (13 ft)
wide, in order to uniformly compact the mix using rollers of normal width, it is necessary to overlap the edge of the previous roller pass by a minimum of 150 mm (6 in.). Vibratory rollers used for most highway paving projects typically are manufactured in three drum widths: 1.67, 1.98, and 2.13 m (66, 78, or 84 in., respectively).