What is 'embankment' in the context of highway construction?

In the context of highway construction, an embankment refers to a raised structure constructed using soil or similar materials to support the roadbed or pavement surface. This structure is critical in creating a stable foundation for the roadway, especially in areas where the natural ground is too low or unstable to support a road directly. The embankment is built to provide elevation, improve drainage, and ensure the longevity and safety of the highway.

The process involves carefully selecting and compacting soil materials to achieve the desired height and strength required to bear the weight of vehicles and withstand various environmental conditions. Proper construction of an embankment is essential, as it must also promote effective drainage to prevent erosion and water accumulation, which can undermine the road's integrity over time.

The other options do not accurately describe embankments. Bridges are structures that span obstacles such as rivers or valleys and have a different purpose. A layer of asphalt pertains to the surface material of the roadway, which serves as a wearing course but does not refer to the foundational support structure like an embankment. Road grading is a method used to level or shape the surface of the ground before construction but does not involve the creation of the raised structure that an embankment represents.