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.

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:

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