Permanent way on sharp curves: What is the standard clearance between the inner running rail and its check rail provided on sharp curves?

Introduction / Context:
Check rails (guard rails) are installed on sharp curves and at special trackwork to control flange movement and prevent flange climb. The clearance between the inner running rail and the check rail must be carefully selected to guide the wheelset without excessive contact or wear.

Given Data / Assumptions:

• Sharp curve installation requiring a check rail.
• Standard practice values for check rail clearance in millimetres.

Concept / Approach:
Too small a clearance causes continuous rubbing and rapid wear; too large a clearance defeats the guiding function. Typical railway practice prescribes about 44 mm on sharp curves to balance guidance and clearance.

Step-by-Step Solution:

Verification / Alternative check:
Standard exam references and maintenance manuals list ~44 mm as the typical check rail clearance for sharp curves, with slight adjustments for gauge and traffic conditions.

Why Other Options Are Wrong:

• 40 or 42 mm: Can be too tight, increasing wear and noise.
• 46 or 50 mm: May be too loose to provide reliable flange guidance.

Common Pitfalls:

• Not distinguishing between straight track check rail use (rare) and sharp curve practice.
• Confusing check rail clearance with flangeway clearance at level crossings.

Final Answer:
44 mm