For hill roads, what is the maximum super-elevation (rate of transverse tilt) that should not be exceeded to ensure safety and vehicle stability?

Introduction / Context:
Super-elevation is the transverse inclination provided on horizontal curves to counteract the centrifugal force on vehicles. On hill roads, geometric constraints and low-speed regimes allow a higher limiting super-elevation than in plains, but it must still be capped for safety and comfort, especially in wet or icy conditions.

Given Data / Assumptions:

• Facility: hill roads with horizontal curves.
• Objective: determine the codal upper limit of super-elevation.
• Vehicles travel at moderate speeds; friction and drainage considerations apply.

Concept / Approach:
IRC recommendations permit a higher limit for hill roads compared to plain terrain to accommodate sharper curves, typically up to 10%. This value balances vehicle stability, skid resistance, and construction practicality on mountainous alignments.

Step-by-Step Solution:
Select hill-road context.Apply the IRC limiting value for e_max on hill roads.Adopt e_max = 10% for design checks and detailing.

Verification / Alternative check:
Empirical practice across Indian hill highways adopts 10% as the ceiling, whereas plains frequently limit e to about 7% due to higher design speeds and comfort constraints.

Why Other Options Are Wrong:

• 5%, 7%, 8%: lower than allowed in hills; may be uneconomical on tight curves.
• 15%: too steep for comfort and safety in most conditions.

Common Pitfalls:

• Providing excessive e on stretches prone to snow/ice, which can cause downslope skidding.
• Ignoring transition lengths for super-elevation runoff.

Final Answer:
10%