What does a solid double yellow line indicate?

A solid double yellow line indicates that no passing is allowed in either direction. This marking is used in areas where visibility is limited or where it is unsafe to overtake another vehicle due to road conditions, traffic, or other factors. It serves as a clear warning to drivers to maintain their lane and refrain from passing, ensuring safety for both the driver and other road users.

In contrast, other options suggest scenarios that do not align with the meaning of a double yellow line. For instance, passing allowed in both directions contradicts the purpose of the double line, while the idea of crossing for left turns or indicating a speed limit change is not accurate for this specific road marking.