On Indian Broad Gauge, gauge widening on curves is generally provided when the degree of curve is:

Introduction / Context:
Gauge widening on sharp curves helps reduce flange binding and limits wheel/rail wear. It is a standard geometric correction applied on tighter curves in Indian Railways.

Given Data / Assumptions:

• Degree of curve is measured by standard railway convention.
• Broad Gauge practice is referenced.
• Typical threshold used in exams is around 3°.

Concept / Approach:

Tighter curves (higher degree) cause higher lateral forces and flange contact. A small intentional widening of gauge eases passage, especially for long-wheelbase rolling stock. Hence, beyond a threshold sharpness, widening is provided.

Step-by-Step Solution:

Verification / Alternative check:

Design tables specify actual widening versus degree; many texts quote 3° as the indicative starting point for BG, with greater widening as degree increases.

Why Other Options Are Wrong:

“3° or less” is usually unnecessary; “between 3° and 4° only” is too restrictive; “not required” is incorrect; “more than 1° on straight track” is nonsensical.

Common Pitfalls:

Confusing degree of curve with cant; applying excessive widening without checking limits and wheelbase considerations.

Final Answer:

More than 3°