Four-lane divided highways: To prevent head-on collisions between vehicles moving in opposite directions, which measure is primarily adopted on such roads?

Introduction / Context:
Head-on collisions are among the most severe crash types because closing speeds are high. Highway engineers therefore design four-lane facilities as divided carriageways so opposing streams are fully separated. The question asks which measure specifically addresses head-on collisions on four-lane roads.

Given Data / Assumptions:

• A four-lane road carries two lanes in each direction.
• Opposing streams are to be separated to prevent encroachment into the opposite carriageway.
• Standard traffic control devices like markings may supplement, but not replace, physical separation for high-speed facilities.

Concept / Approach:

Centerline (or lane) markings provide guidance but cannot physically block errant vehicles. A raised, landscaped, or barrier median forms a continuous longitudinal separator. This median (also called a physical divider) is the primary design element to prevent head-on conflicts by eliminating opposing traffic face-to-face interaction on the same carriageway.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals for divided highways emphasize a central median or continuous longitudinal barrier as the definitive treatment for eliminating head-on conflicts on multi-lane high-speed facilities. Markings alone are insufficient at higher speeds or volumes.

Why Other Options Are Wrong:

• Markings on the road: provide delineation but no physical separation; cannot reliably prevent head-on crashes.
• Area dividers: a vague term for pavement markings/islands; not a continuous physical separator.
• None of these: incorrect because medians are the standard solution.

Common Pitfalls:

• Confusing lane markings with medians; markings help guidance, not physical crash prevention.
• Assuming urban channelization islands are equivalent to highway medians; islands are intermittent and local.

Final Answer:

Medians of wide area are provided.