What does a single broken white line on the highway mean?

Answer: D — Traffic flows in the same direction

A single broken white line on the highway indicates that traffic flows in the same direction on both sides of the line, and it also allows for lane changes. Drivers are permitted to cross this line to change lanes, as long as it is safe to do so. This marking helps to delineate lanes without imposing restrictions, making it clear that multiple lanes are designated for the same direction of travel. The other options correspond to different traffic indicators. A solid line would suggest a restriction against passing, while "do not enter" typically indicates areas where vehicles cannot legally enter. A one-way street is marked differently to indicate that traffic must travel in a single direction only, making it important for drivers to recognize these distinctions to ensure safe and compliant driving.