According to IRC terrain classification based on cross slope, a country with cross slope between 10% and 25% is categorized as which type of terrain?

Introduction / Context:
Terrain classification influences design speed, ruling gradient, curvature, sight distance, and earthwork quantities in highway alignment design. The Indian Roads Congress (IRC) classifies terrain primarily by the natural cross slope of the ground, enabling designers to adopt appropriate geometric standards and cost expectations.

Given Data / Assumptions:

• Cross slope band considered: 10% to 25%.
• IRC-based categorization sought (plain, rolling, mountainous, steep).

Concept / Approach:
IRC adopts cross-slope ranges roughly as: Plain (0–10%), Rolling (10–25%), Mountainous (25–60%), and Steep (> 60%). These ranges reflect increasing construction difficulty and tighter geometric compromises as cross slope rises. Rolling terrain allows moderate speeds with reasonable earthwork, while mountainous and steep terrain require restrictive standards and more structures (retaining walls, hairpin bends).

Step-by-Step Solution:
Match the given cross-slope band 10–25% to the IRC table. Find the corresponding category: Rolling. Select “Rolling” as the correct answer.

Verification / Alternative check:
Project feasibility reports routinely adopt rolling standards for this slope band, reflected in chosen design speeds and curvature limits on state and national highways crossing undulating plateaus and foothills.

Why Other Options Are Wrong:

• Plain: 0–10% only.
• Mountainous: 25–60%—steeper than the stated band.
• Steep: > 60%—very rugged terrain.

Common Pitfalls:

• Mistaking local short gradients for average terrain classification—use cross slope, not isolated road gradients.

Final Answer:
Rolling.