Track maintenance access: What is the minimum packing (tamping) space typically provided between two sleepers to allow effective maintenance?

Introduction / Context:
Efficient tamping of ballast under sleepers requires adequate lateral space between adjacent sleepers for inserting tamping tools (manual or machine tines). Too little spacing hampers compaction quality; too much reduces sleeper density and track stiffness.

Given Data / Assumptions:

• Mainline track with standard sleeper dimensions.
• Manual or mechanized tamping operations.
• Ballast depth and crib dimensions are within standard practice.

Concept / Approach:
The packing space (crib width) must allow tools to penetrate and compact ballast effectively. A commonly adopted minimum is about 30 to 35 cm. This balances maintainability with sleeper spacing needed for structural support and load distribution.

Step-by-Step Solution:
1) Identify maintenance requirement: tool/tine insertion and manipulation.2) Provide crib width ~30–35 cm to meet this need.3) Ensure uniformity along the track to maintain consistent support conditions.

Verification / Alternative check:
Track handbooks and mechanized maintenance guidelines adopt crib widths near 30–35 cm for effective tamping and drainage while maintaining sleeper density for stiffness.

Why Other Options Are Wrong:

• 20–30 cm: often too tight for efficient tamping, especially mechanized tines.
• 35–40 cm or more: reduces sleeper density for a given rail seat loading unless spacing is redesigned.

Common Pitfalls:

• Cramming ballast without leaving sufficient crib width—leads to poor compaction and voids.
• Non-uniform crib widths causing differential settlement.

Final Answer:
30 to 35 cm.