Permanent way: As per Railway Board practice, a diamond crossing should not be flatter than which crossing number (1 in N)?

Introduction / Context:
A diamond crossing is formed where two tracks cross each other at grade. The “flatness” is expressed by the crossing number 1 in N (cotangent of the crossing angle). Operational safety and wear considerations limit how flat (large N) such crossings may be.

Given Data / Assumptions:

• Standard Indian Railways guidance for broad-gauge conditions.
• “Not flatter than” means the minimum permissible crossing number (upper bound on flatness).

Concept / Approach:
Flatter crossings (larger N) lead to longer wheel–rail contact paths on the crossing nose and wings, increasing impact/wear and complicating maintenance. Hence, a minimum sharpness (smaller N) is mandated to confine impact zones.

Step-by-Step Solution:
Recall the commonly adopted minimum: 1 in 8.5 for diamond crossings.Compare with alternatives: 1 in 6 is sharper, but practice typically restricts diamonds from being flatter than 1 in 8.5.Select 1 in 8.5 as the limiting flatness.

Verification / Alternative check:
Permanent-way manuals and question banks consistently quote 1 in 8.5 as the limiting flatness for diamonds under typical conditions.

Why Other Options Are Wrong:

• 1 in 6: Sharper than necessary; not the flatness limit.
• 1 in 12 or 1 in 16 or 1 in 20: Flatter than the allowed limit and thus not permitted as a minimum.

Common Pitfalls:
Confusing turnout sizes with diamond crossing limits; misreading “not flatter than.”

Final Answer:
1 in 8.5