Hill roads – minimum vertical clearance What is the minimum vertical clearance that should be provided under overhanging cliffs or other obstructions above the surface of a hill road?

Introduction / Context:
Adequate vertical clearance on hill roads ensures safe passage of buses, trucks, and emergency vehicles and reduces collision risk with overhangs or structures.

Given Data / Assumptions:

• Standard vehicle envelopes for intercity traffic.
• Provision under rock overhangs or built structures on hill alignments.

Concept / Approach:
Typical guidance adopts a minimum of about 4.5 m for safe clearance in such locations, considering vehicle heights, dynamic movements, and construction tolerances.

Step-by-Step Solution:
Select the value meeting standard clearances.4.5 m satisfies typical heavy vehicle envelopes.

Verification / Alternative check:
Bridge and underpass clearances on highways commonly use similar minimum values in many jurisdictions.

Why Other Options Are Wrong:

• 3 m and 4 m: inadequate for buses and trucks.
• 5 m and 6 m: safe but not the minimum standard; they increase cost and excavation need.

Common Pitfalls:
Ignoring allowances for resurfacing thickness or snow compaction which reduce effective clearance if not considered.

Final Answer:
4.5 m