For hill roads around 300 m above mean sea level (MSL), the ruling gradient commonly adopted is:

Difficulty: Easy

Correct Answer: 5%

Explanation:


Introduction / Context:
Gradient selection in hilly terrain balances vehicle power limits, safety, and earthwork costs. The ruling gradient is the preferred maximum used for most of the route, with limiting and exceptional gradients reserved for constrained sections.


Given Data / Assumptions:

  • Hill road near 300 m elevation (moderate altitude).
  • Target: typical ruling gradient for design in such terrain.


Concept / Approach:
Ruling gradients for hilly/mountainous roads are steeper than for plains, but still need to be comfortable for heavy vehicles. Values around 5% are commonly adopted as ruling, with limiting 6% and exceptional up to 7% for short stretches where topography dictates.


Step-by-Step Solution:
Identify context: hilly terrain, moderate elevation.Adopt ruling gradient ≈ 5% (1 in 20).Use limiting/exceptional gradients only where necessary to control earthwork and land impacts.


Verification / Alternative check:
Vehicle gradeability, especially for loaded trucks and buses, suggests that maintaining gradients near 5% promotes safe speeds and manageable power demands while avoiding excessive hairpins and long detours.


Why Other Options Are Wrong:

  • 4%: conservative; increases road length and cost in hills.
  • 6% and 7%: align with limiting/exceptional, not ruling.
  • 8%: too steep for routine ruling gradient; used only under special constraints for very short lengths.


Common Pitfalls:

  • Applying plain-terrain gradients to hill roads.
  • Overusing exceptional gradients, which impair heavy vehicle performance and safety.


Final Answer:
5%

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