Sleeper cant near the rail seat: On either side of the centre line of the rail, a cant of 1 in 20 is provided in the sleeper for a distance of

Introduction / Context:
Rail seats on sleepers are adzed or formed to a 1 in 20 cant to match the rail base inclination. This improves wheel–rail contact by aligning the rail head with the conicity of wheels and reduces flange wear and rolling contact stresses.

Given Data / Assumptions:

• Standard flat-bottom rail with 1 in 20 base inclination.
• Timber or concrete sleeper with defined rail seat width.
• Distance measured from the rail centre line on both sides.

Concept / Approach:
The adzed/canted area must extend sufficiently beyond the rail base to ensure uniform support and prevent edge crushing of sleeper fibres or pads. A typical provision is 150 mm on either side of the rail centre line, covering and slightly exceeding the rail base width for robust support.

Step-by-Step Solution:
Identify rail base width and pad/plate footprint.Provide a canted seat width that fully supports the rail base with margin.Adopt the standard value of 150 mm from rail centre line on each side.

Verification / Alternative check:
Permanent-way specifications list the canted seat width near 300 mm total around the rail centre line, i.e., 150 mm on each side, ensuring full bearing under dynamic loads.

Why Other Options Are Wrong:

• 165 mm, 175 mm, 185 mm: Wider seats may be used in special designs, but the standard provision is 150 mm each side.

Common Pitfalls:
Confusing total seat width with distance from centre line; mixing the 1 in 20 rail seat cant with track superelevation (cant) on curves.

Final Answer:
150 mm