Rail selection factors — the weight per metre of rails adopted on a route depends upon which design considerations?

Introduction / Context:
Choosing the rail section (weight per metre) is a fundamental step in permanent way design. Heavier rails better resist bending and wear but cost more. The optimum choice balances traffic demands, support conditions, and economics, considering multiple interacting factors.

Given Data / Assumptions:

• Factors listed: track gauge, train speed, sleeper spacing (support density), and traffic nature (axle loads, volume).
• Heavier rail sections are typically adopted for heavier, faster traffic with wider sleeper spacing.

Concept / Approach:

Rail is a beam on elastic supports. Bending moments and contact stresses rise with axle load, speed, and support spacing. Wider gauge routes often carry higher loads. Therefore, all listed factors inform the selection of an adequate rail weight to ensure acceptable stress, deflection, and service life.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Design charts and empirical rules in permanent way manuals relate rail section to axle load, speed, sleeper density, and expected tonnage.

Why Other Options Are Wrong:

Focusing on a single factor ignores the multi-parameter nature of rail selection; no single factor suffices across all routes.

Common Pitfalls (misconceptions, mistakes):

Overemphasizing gauge or speed alone; neglecting sleeper spacing and cumulative traffic tonnage.

Final Answer:

all the above