No-passing (overtaking) zones: On which road element are passing (overtaking) zones generally not provided because of restricted sight distance and safety concerns?

Introduction / Context:
No-passing zones are portions of roadway where overtaking is prohibited for safety due to limited sight distance or complex maneuvers. Identifying where to restrict passing is an essential part of traffic control and road marking design.

Given Data / Assumptions:

• Focus on geometric elements that limit sight distance.
• Two-lane undivided highways are typical contexts for passing zones.

Concept / Approach:
Horizontal curves frequently limit sight distance due to roadside obstructions and curvature itself. Crest vertical curves can also reduce sight distance, but properly designed crests ensure stopping sight distance; passing sight distance requirements are much longer and are especially hard to meet on horizontal curves, making them common locations for no-passing markings.

Step-by-Step Solution:
Evaluate sight distance on each element: horizontal curves often provide the least.Apply passing sight distance criteria: rarely satisfied on sharp horizontals.Therefore, designate no-passing zones on horizontal curves.

Verification / Alternative check:
Marking manuals and IRC guidelines show continuous centerlines (no-passing) at horizontal curves, near intersections, on approaches to summits where PSD is inadequate, and on bridges. Among the options, horizontal curves are the most general answer.

Why Other Options Are Wrong:

• Summit curves: sometimes allow passing if sight distance is ample; not “generally” prohibited in all cases.
• Two-lane highways anywhere: incorrect—many straight sections provide adequate PSD.
• All the above/none: do not reflect practice-based distinctions.

Common Pitfalls:

• Confusing stopping sight distance sufficiency with passing sight distance sufficiency.
• Ignoring roadside vegetation/barriers that further restrict horizontal curve SSD/PSD.

Final Answer:
horizontal curves