What does a solid double yellow line indicate?

A solid double yellow line indicates that no passing is allowed in either direction. This marking serves as a vital safety measure, particularly on two-lane roads where visibility may be limited or where it is otherwise unsafe to overtake another vehicle. The presence of this line signifies that drivers should remain in their respective lanes and not attempt to pass other vehicles, as doing so could lead to dangerous situations, such as head-on collisions.

In contrast, options related to passing being allowed or indicating lane changes reflect situations where it is safe or permissible to maneuver within the roadway, which is not the case with solid double yellow lines. The emphasis on the "no passing" rule reinforces the importance of adhering to traffic regulations for maintaining safety on the roads.