Why is the unconfined edge of the first HMA pass often the lowest-density part of the mat?

1. The unconfined edge has no adjacent material to push against, so the roller cannot develop the same confinement as in the middle of the lane
2. Nuclear gauges cannot be used within 10 feet of any edge, so the edge is never rolled
3. Tack coat is always omitted within 3 feet of the edge
4. The paver screed is thicker at the edges than in the center