What does a solid double yellow line signify?

A solid double yellow line signifies that no passing is allowed in either direction. This traffic marking is used to indicate a clear prohibition against overtaking or passing other vehicles, as it typically represents a roadway with conditions that may be hazardous for such maneuvers, such as curves or limited visibility. The message of safety is paramount in these areas, ensuring that drivers are aware that they must remain in their lanes without attempting to pass other vehicles, regardless of the direction they are traveling in.

The other options mention scenarios that either allow passing or designate specific vehicle types for passing, which does not align with the established meaning of a solid double yellow line in traffic regulations. Thus, understanding this road marking helps promote safer driving practices and adherence to traffic laws.