Super-elevation policy in snow-bound regions: what should be taken as the practical upper limit for super-elevation on such roads to reduce skidding risk?

Introduction / Context:
Super-elevation (crossfall on curves) counteracts lateral acceleration. In snow-bound areas, excessive super-elevation can increase skidding risk on icy surfaces, particularly toward the valley side on hill roads. Hence, a conservative practical upper limit is adopted.

Given Data / Assumptions:

• Road experiences snow/ice conditions for part of the year.
• Friction is significantly reduced during winter.
• Safety and vehicle stability govern the choice of maximum super-elevation.

Concept / Approach:
With reduced friction, lateral stability must be ensured without creating a crossfall so steep that vehicles lose lateral control. A cap around 7% is a widely accepted limit in snow-bound practice, balancing centripetal demand and skid resistance.

Step-by-Step Solution:

Verification / Alternative check:
Safety audits and winter performance records show that limiting super-elevation reduces outward skidding events on icy curves.

Why Other Options Are Wrong:
15%, 12%, and 10% are too steep for low-friction, icy conditions; 6% is more conservative than typical practice but may be unnecessarily restrictive for some sites.

Common Pitfalls:
Applying general maximum super-elevation without considering climate; ignoring the friction reduction due to snow and ice.

Final Answer:
7%