What does a solid yellow line indicate?

A solid yellow line serves as a critical road marking indicating a no passing zone. This line indicates that passing other vehicles is prohibited for safety reasons, typically due to lack of visibility or the presence of oncoming traffic. It emphasizes that drivers should not cross over the line to overtake another vehicle, as doing so could lead to dangerous collisions.

The no passing designation is especially important in areas where visibility is limited, such as curves or hills, where it would be unsafe to attempt to pass. This is designed to protect both the driver attempting to pass and the oncoming traffic.

The other options present incorrect contexts for the solid yellow line. For instance, allowing double lane changes or passing contradicts the safety message conveyed by the solid yellow line. Staying in your lane is a general practice across various road markings but is not specifically what the solid yellow line indicates. The term "danger zone" is vague and does not accurately define the meaning of a solid yellow line on the roadway.