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?
-
A15%
-
B12%
-
C10%
-
D7%
-
E6%
Answer
Correct Answer: 7%
Explanation
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:
Recognize that higher super-elevation improves balance on dry roads but can be unsafe on ice.Adopt a lower cap in snow-bound regions; 7% is the practical upper limit used in many design guides.Hence select 7% from the options.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%