For a Broad Gauge (B.G.) single-track railway tunnel, what should be the typical clear height above top of rails (TOR) to accommodate rolling stock and services?

Difficulty: Easy

5.5 m to 5.8 m
5.8 m to 6.2 m
6.7 m to 7.3 m
7.3 m to 7.5 m
6.2 m to 6.5 m

Correct Answer: 6.7 m to 7.3 m

Explanation:

Introduction / Context:
Tunnel vertical clearance must safely envelope the dynamic outline of trains, overhead equipment (if electrified), ventilation ducts, and maintenance space. For B.G. single track, a clear-height band has emerged from practice to balance safety, equipment needs, and excavation economy.

Given Data / Assumptions:

Gauge: Broad Gauge (single track).
Reference: height above top of rails (TOR).
Assume standard rolling stock and typical service provisions.

Concept / Approach:
The 6.7–7.3 m band accommodates train sway, overhead fixtures, and cable/duct allowances without excessive over-excavation. Lower bands may suffice in specific non-electrified contexts, but the stated range is a robust general guideline in planning and exam contexts, particularly where room for ventilation ducts or emergency systems is needed.

Step-by-Step Solution:

Identify TOR as the vertical datum for clearances.Include dynamic envelope, OHE (if applicable), and safety margins.Select the recognized safe band: 6.7 m to 7.3 m above TOR.

Verification / Alternative check:

Cross-sections of typical B.G. tunnels with OHE and walkways fit within this envelope while preserving aerodynamic and smoke clearance considerations.

Why Other Options Are Wrong:

Bands below 6.7 m risk inadequate space for equipment and safe clearances.Values beyond 7.3 m are conservative and raise excavation costs without generic justification.

Common Pitfalls:

Forgetting to check special rolling stock or emergency ventilation requirements that might push toward the upper end of the band.

Final Answer:

6.7 m to 7.3 m

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For a Broad Gauge (B.G.) single-track railway tunnel, what should be the typical clear height above top of rails (TOR) to accommodate rolling stock and services?

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