Ruling gradient and reduction in vehicle load capacity: choose the correct percentage reduction corresponding to the stated gradient.

Introduction / Context:
On upgrades, the tractive effort available must overcome grade resistance. A practical thumb rule used in transport engineering is that the percentage reduction in load capacity is approximately equal to the grade (rise per 100) for moderate slopes.

Given Data / Assumptions:

• Ruling gradient options: 1 in 10, 1 in 15, 1 in 20, 1 in 25.
• Assume moderate speeds and typical commercial vehicles.
• Reduction in load capacity roughly equals the grade percentage.

Concept / Approach:
Grade 1 in n corresponds to a slope of (1/n). As a percentage, this is (100/n)%. The reduction in load capacity is approximated by this percentage for quick checks in highway planning.

Step-by-Step Solution:

Verification / Alternative check:
The rule aligns with grade resistance per tonne being proportional to the slope, so doubling n halves the approximate percent reduction.

Why Other Options Are Wrong:
They misinterpret the reduction as equal to n instead of 100/n, leading to unrealistic high reductions for gentle grades.

Common Pitfalls:
Confusing “1 in n” with “n percent”; forgetting that percent grade is (100/n)%.

Final Answer:
For 1 in 10, reduction is 10%