To reduce impact on the nose of crossing, wing rails are “ramped” so that the nose sits slightly lower than the wing rails. By how much is the nose typically kept lower?

Introduction / Context:
At a crossing (frog), wheel transfer from wing rail to nose can cause impact. A small vertical offset (ramping) is used so the wing rail carries the wheel slightly before the nose engages, protecting the nose from direct hammering.

Given Data / Assumptions:

• Standard BG turnout and crossing practice.
• Typical workshop/maintenance tolerances apply.

Concept / Approach:

Providing a small lead height to wing rails reduces impact on the nose. A commonly adopted nominal difference is about 6 mm, balancing reduced impact with smooth transition.

Step-by-Step Solution:

Verification / Alternative check:

Turnout maintenance manuals specify permissible height differences and ramp lengths; 6 mm appears as a standard nominal figure.

Why Other Options Are Wrong:

3–5 mm may be insufficient in many practices; >6 mm could cause a perceptible step and ride deterioration.

Common Pitfalls:

Assuming no ramping is needed; over-ramping causing dynamic shock.

Final Answer:

6 mm