What does the term "crowning" refer to in grading?

Crowning refers to shaping the road surface such that it has a higher point at the center and slopes down toward the edges. This design is crucial for effective water runoff, as it helps direct rainwater away from the road surface and toward the ditches or shoulders. By ensuring that the road has this rounded profile, crowning plays a vital role in preventing water from pooling on the surface, which can lead to erosion, potholes, and other forms of road degradation.

In contrast, creating a slope for water drainage, while somewhat related, does not specifically describe the shaping or contouring involved in crowning. Adding material to the edges of the road primarily concerns raising the edges rather than the central portion, and compacting the base layer focuses on preparing the underlying support rather than shaping the surface for runoff. Each of these options addresses aspects of road maintenance and construction but only crowning directly pertains to the specific contouring of the road surface for effective water management.