An asphalt plant will produce 180 tph for a highway project. The mat will be 12 ft wide and 1 
-in. thick, and will have a density of 110 lb/sy-in. A vibratory roller with a 84-in. wide drum will be used for compaction. Assume a 60-min hour efficiency factor for the roller. The overlap between adjacent laps and over edges will be 6-in. minimum.
It is estimated that nonproductive travel will add about 15% to total travel. From a test mat, it was found that three passes with the roller are required to achieve density.
To account for acceleration and deceleration when changing directions, add 10% to the average roller speed to calculate a running speed. If it is desired to keep the rolling speed under 3 mph, how many rollers are required for the project?