Terrain classification by cross slope: If the natural cross slope of a country is up to 10%, the terrain is classified as what for highway planning purposes?

Introduction / Context:
Terrain classification affects design speed, gradient, curvature, and cost of a highway. Standard categories are based on the natural ground cross slope, which influences earthwork volumes and alignment flexibility.

Given Data / Assumptions:

• Cross slope threshold up to 10%.
• Conventional Indian practice for terrain classes.
• Used for geometric design and project costing.

Concept / Approach:

Typical bands are: Plain (0–10%), Rolling (10–25%), Mountainous (25–60%), and Steep (>60%). These reflect construction challenges and achievable design speeds. At up to 10% cross fall, the alignment can generally be laid with modest earthwork and mild gradients—classified as plain terrain.

Step-by-Step Reasoning:

Verification / Alternative check:

Planning guidelines and geometric design manuals use these bands to set base design speeds and gradient limits; up to 10% clearly falls in the Plain category.

Why Other Options Are Wrong:

• Rolling, Mountainous, Steep: correspond to greater cross slopes producing tighter curves and steeper grades.

Common Pitfalls:

• Interpreting longitudinal gradient limits as terrain class; classification is by natural cross slope, not designed grade.

Final Answer:

Plain.