What is the primary purpose of a solid yellow line on the road?

The primary purpose of a solid yellow line on the road is to separate lanes of traffic moving in opposite directions. This line serves as a critical safety measure, indicating that overtaking or passing is not permitted when the solid yellow line is present. It helps prevent head-on collisions by clearly designating where vehicles should operate in relation to oncoming traffic. When drivers see a solid yellow line, it signals them to stay in their lane and be cautious of opposing traffic, which is essential for safe driving conditions on roads that do not have physical barriers separating opposing lanes. Other options, such as indicating a speed limit, separating lanes of traffic moving in the same direction, or indicating a parking lane, do not accurately reflect the function of a solid yellow line.