On hill roads where several hairpin bends are necessary, what minimum intervening distance between successive hairpin bends is generally maintained to ensure safety and stability?

Introduction / Context:
Hairpin bends (switchbacks) are sharp 180-degree turns used to rapidly gain elevation on steep terrain. Spacing these bends properly is essential for safety, sight distance, vehicle maneuverability, and slope stability.

Given Data / Assumptions:

• Standard two-lane hill road geometry.
• Typical design vehicles include buses and medium trucks.
• Terrain and right-of-way permit recommended spacing.

Concept / Approach:
Providing a minimum intervening distance helps in accommodating transition lengths, superelevation runoff, driver comfort, and drainage works between curves. A commonly adopted minimum is about 60 m under Indian hill-road practice.

Step-by-Step Solution:

Verification / Alternative check:
Where terrain allows, larger spacing (e.g., 100 m) may be used for improved comfort; however, 60 m is widely accepted as the lower bound.

Why Other Options Are Wrong:
20–40 m are too short for safe transitions and sight distance; 100 m, while safe, is not the typical minimum and may be impractical in steep terrain.

Common Pitfalls:
Placing bends too close due to right-of-way constraints; neglecting super-elevation runoff length between successive hairpins.

Final Answer:
60 m