Service life of timber sleepers: Which factors primarily govern the life of a wooden sleeper in track?

Introduction / Context:
Wooden sleepers remain in service in many networks for sidings and low-density lines. Their service life varies widely due to material properties and environment. Understanding the key determinants aids procurement and maintenance planning.

Given Data / Assumptions:

• Sleeper life is influenced by both inherent wood characteristics and external conditions.
• Proper treatment (creosote/CCA) and drainage practices assumed to be standard.

Concept / Approach:
Durable species with good density and strength resist crushing and splitting. Preservative treatment and seasoning combat fungi and insects. Exposure to moisture cycles, UV radiation, and temperature affects checking and decay; ballast drainage and maintenance mitigate these effects.

Step-by-Step Solution:
Quality: Strong, defect-free timber better resists mechanical stresses from traffic.Decay resistance: Proper preservative treatment substantially increases life.Weathering resistance: Good detailing and ballast drainage reduce wet–dry cycles and rot.

Verification / Alternative check:
Field records show large life variability (often 7–25 years) depending on the three factors; improved treatment and drainage correlate with longer life.

Why Other Options Are Wrong:
No single factor can guarantee life; the combined influence is decisive, hence “All of the above”.

Common Pitfalls:

• Focusing only on species and ignoring preservative treatment quality.
• Neglecting drainage, leading to premature rot despite good timber.

Final Answer:
All of the above