Under what condition is it legal for a driver to pass another vehicle on a two-lane road?

Passing another vehicle on a two-lane road is legal when there is a single broken yellow line. This marking indicates that the lane is open for passing and that it is permissible for a driver to cross the line to overtake a slower vehicle, provided it is safe to do so. When approaching a single broken yellow line, drivers should ensure that the road ahead is clear of oncoming traffic and that it is safe to execute the maneuver.

The other options indicate situations that typically would not legally allow a driver to pass. A double yellow line denotes that passing is not allowed due to safety concerns, often because of limited visibility. A speed limit over 55 mph does not inherently permit passing; it is the road markings that dictate legality. Lastly, while a clear road is generally needed to safely pass, it is the presence of a single broken yellow line that specifically communicates that passing is permitted. Thus, ensuring both the roadway marking and the conditions are met is crucial for safe driving practices.