Permissible gauge under loaded condition (tolerance) on a Broad Gauge track is typically limited to which of the following values?

Introduction / Context:
Gauge tolerance under load ensures that track retains safe wheel guidance despite elastic deformations. Indian Railways specifies acceptable variations so that maintenance targets are clear and rolling stock safety margins are preserved.

Given Data / Assumptions:

• B.G. track under service loading.
• Typical permissible widening is small and positive; tightening (negative) is rarely specified as desirable under load.

Concept / Approach:

Under load, rail fastenings and sleeper seats experience elastic movement. Standards set a small upper bound to gauge widening—commonly taken as about +6 mm for exam purposes—beyond which corrective maintenance is required.

Step-by-Step Solution:

Verification / Alternative check:

Track maintenance manuals and permanent-way instructions provide tables of tolerances; +6 mm is a representative upper limit used in many contexts for BG.

Why Other Options Are Wrong:

+3 mm is tighter than typical exam standard; zero tolerance is impractical; negative tolerance (tightening) is unsafe; −20 mm is grossly unacceptable.

Common Pitfalls:

Confusing construction tolerances (no load) with service tolerances (under load); misapplying gauge-widening for curves to straight track tolerances.

Final Answer:

G + 6 mm