Difficulty: Easy
Correct Answer: 4.9 m to 5.5 m
Explanation:
Introduction / Context:Tunnel cross-sections for railways must provide safe clearances for dynamic envelope, electrification equipment (if any), maintenance walkways, and aerodynamic effects. For Broad Gauge single track, standard practice converges to a moderate width band that balances construction economy with operational safety.
Given Data / Assumptions:
Concept / Approach:Clear width reflects track centerline allowances, sway, and lateral clearances. Typical guidance for B.G. single track sits in the 4.9–5.5 m range, accommodating dynamic sway and minor maintenance space while keeping excavation volumes reasonable. Larger widths are reserved for special provisions (walkways both sides, heavy electrification fixtures) or future-proofing decisions.
Step-by-Step Solution:
Define the dynamic envelope and lateral clearances for B.G. stock.Include tolerances for track alignment, construction, and side drainage.Select the established width band: 4.9 m to 5.5 m.Verification / Alternative check:
Cross-section checks for typical B.G. rolling stock show this band sufficient for non-electrified and many electrified corridors with compact fittings.Why Other Options Are Wrong:
4.2–4.8 m: may under-provide lateral clearance.5.5–5.8 m or larger: wider than typical baseline; increases excavation without necessity in many cases.Common Pitfalls:
Ignoring special allowances (walkways, cable trays) that may push designers toward the top of the band.Final Answer:
4.9 m to 5.5 m
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