Compaction is critical to reducing the permeability of the mat to give it greater fatigue life. Roller operators have found that they, too, need to be cautious in their work. If they happen to roll off the new mat just a little and the rollers touch even a small bump on the roadway edge, that bump is transferred across the roller to the inboard side, and the bump is mirrored into the new surface. On our first job, we kept getting bumps on our mat, and we couldn't figure out what it was. We marked every time the machine stopped, every time we dumped a truck, every time a roller pulled off the mat.
Rollers have to be operated according to accepted practice and never parked on the mat.
With the paver moving at a slower speed, the rollers can easily keep up and compaction is improved. A lift of paving is a second opportunity. Another lift of paving would be a third opportunity. So we count the number of opportunities, thinking we can improve the mat a certain percentage with each opportunity. Many contractors support the ADOT model.