Limit on superelevation in rolling terrain (plains) For highways in rolling terrain across plains, the maximum allowable superelevation (as a percentage) is generally limited to:

Introduction / Context:
Superelevation tilts the pavement to counter lateral acceleration on curves. Design codes cap its value to ensure vehicle stability at low speeds, drainage compatibility, and safety in icy/wet conditions.

Given Data / Assumptions:

• Rolling terrain (plains context).
• Bituminous or concrete pavement; normal traffic mix.

Concept / Approach:
Typical guidelines limit maximum superelevation in plains to about 7%. In hilly or snow-free areas higher limits (e.g., 10%) may be permitted, but in plains the cap is lower to balance opposing needs.

Step-by-Step Solution:

Verification / Alternative check:
Calculated e from e = V^2/(225R) must also be checked not to exceed this cap; if it does, increase radius or manage speed/transition length.

Why Other Options Are Wrong:
4–6% are below the common cap and may be unnecessarily restrictive; 10% reflects hilly/special contexts.

Common Pitfalls:
Using the higher hilly-area cap in plains; forgetting to verify runoff length and shoulder crossfall compatibility.

Final Answer:
7%