What does a solid double yellow line signify?

A solid double yellow line signifies that no passing is permitted in either direction. This marking is used on roads to indicate that it is unsafe to overtake another vehicle, often due to factors like limited visibility or heavy traffic conditions. The double lines reinforce the message that both lanes of traffic should remain in their respective paths without attempting to pass, enhancing the safety of all road users.

In contrast, the other options provide misleading interpretations of the solid double yellow line's meaning. For example, passing allowed with caution implies that drivers may navigate around other vehicles under certain conditions, which is not the case with a solid double line. Moreover, while two-way traffic may occur on the same road where a double yellow line is present, the line itself does not indicate this concept; instead, it's more about signaling the prohibition of passing. Lastly, the option regarding only right turns permitted does not apply here, as the line's purpose is strictly related to passing and doesn't dictate turning maneuvers.