Non-passing sight distance – obstacle height convention In defining non-passing (or stopping-related) sight distance, the standard obstacle height commonly adopted for visibility checks is:

Introduction / Context:
Design sight distance checks use standard eye height and obstacle height values to produce conservative, uniform criteria across projects. For non-passing or stopping-related visibility, a low obstacle height represents debris or a small object on the pavement.

Given Data / Assumptions:

• Driver eye height is typically standardized (e.g., around 1.05–1.2 m in many manuals).
• Obstacle height is chosen small to ensure timely stopping for minor hazards.

Concept / Approach:
While different agencies use slightly different values, many traditional problems adopt an obstacle height of about 0.25 m for conservative checks in non-passing sight distance contexts.

Step-by-Step Solution:

Verification / Alternative check:
Some standards use 0.15 m in SSD calculations; when that value is not listed, the next conservative conventional choice from options is 0.25 m.

Why Other Options Are Wrong:
10 cm may be excessively small relative to typical guidance; 50–150 cm represent larger objects and would overstate available sight distance.

Common Pitfalls:
Confusing passing sight distance criteria (two-vehicle meeting) with SSD obstacle-height conventions.

Final Answer:
25 cm