Geometric design in hills (snow-free): select the minimum radius of curvature typically adopted for National/State highways in hilly regions that are free from snow.
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A60 m
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B50 m
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C33 m
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D30 m
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E25 m
Answer
Correct Answer: 30 m
Explanation
Introduction / Context:Horizontal curvature is constrained by terrain, speed, friction, and super-elevation limits. In hilly regions (snow-free), lower design speeds are permitted, allowing smaller radii—but not so small as to compromise safety and comfort.
Given Data / Assumptions:
- Hilly terrain, snow-free (so higher super-elevation caps than snow-bound areas).
- National/State highway class.
- Low-to-moderate design speeds common for hill roads.
Concept / Approach:Minimum radius is guided by the balance of centrifugal force with side friction and super-elevation. For low design speeds typical in hill roads, practical minimum radii around 30 m are used for absolute controls, with higher values desirable where feasible.
Step-by-Step Solution:
Acknowledge lower speeds permit smaller R while respecting max e and f.Select the smallest safe and commonly adopted absolute minimum in the list.Choose 30 m as the accepted minimum for snow-free hill conditions among the given choices.Verification / Alternative check:Check against typical design tables: absolute minimum radii reduce as design speed reduces; 30 m often appears as the lower bound for constrained hill alignments.
Why Other Options Are Wrong:25 m is generally too small for highway classes; 33–60 m are feasible but the question asks for minimum—30 m matches the common absolute control for this context.
Common Pitfalls:Confusing desirable minimum with absolute minimum; ignoring snow-bound limitations on super-elevation.
Final Answer:30 m