Asphalt driveway drainage — a cross-slope sheds water while a flat driveway ponds and fails
Drainage is the #1 failure mode: a flat driveway ponds water that soaks and ruins the base, while a ~2% cross-slope (plus ≥1% longitudinal grade) sheds it. No ponding, ever.
What this diagram shows
A comparison of two asphalt driveway sections. On the left, a flat driveway holds a puddle of water that ponds on the surface and soaks down into the aggregate base, destroying the base bearing strength so the asphalt cracks and forms potholes. On the right, a driveway built with about a two percent cross-slope sheds water sideways off the edge so the base stays dry and the pavement lasts. The Asphalt Institute recommends a cross-slope of about 1.5 to 3 percent and a longitudinal grade of at least one percent, with no ponding allowed anywhere.
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