Limits on unbalanced speed: What is the maximum cant deficiency generally prescribed on Indian Broad Gauge (BG) railways?

Introduction / Context:
Cant deficiency is the shortfall of provided cant relative to the equilibrium cant needed at a given speed and curve radius. Allowing some cant deficiency enables higher speeds without fully matching equilibrium cant, balancing comfort, safety, and track maintenance needs.

Given Data / Assumptions:

• Route class and vehicle characteristics follow Indian BG standards.
• We consider typical limits used in mainline operations, not exceptional trials.

Concept / Approach:
Passenger comfort and lateral force limits determine the permissible unbalanced lateral acceleration, translating to a cant deficiency cap. For Indian BG, a commonly adopted maximum cant deficiency is approximately 75 mm for general operations, subject to vehicle dynamics and route approvals.

Step-by-Step Solution:
Relate cant deficiency to unbalanced lateral acceleration perceived by passengers.Adopt network-standard cap balancing speed potential and safety.Hence, choose 75 mm as the typical maximum for BG.

Verification / Alternative check:
Vehicle-Track Interaction guidelines and IR codes cite around 75 mm (context-dependent) as the normative maximum, with special cases requiring specific sanction and checks.

Why Other Options Are Wrong:
25–50 mm: Too conservative for most BG mainline standards.100 mm: Exceeds normal comfort/safety envelopes without special sanction.

Common Pitfalls:

• Confusing cant deficiency with cant excess (over-cant at low speeds).
• Applying metro/suburban limits directly to intercity BG contexts.

Final Answer:
75 mm