When may drivers cross the tracks of an unguarded railroad crossing marked by a flashing light after a train has passed?

The correct answer is based on the specific safety protocols surrounding unguarded railroad crossings. Drivers must wait until the flashing red light goes out before proceeding across the tracks. This sign indicates that the train has cleared the area, but it is also essential to ensure that no other trains are approaching from either direction.

The flashing red light serves as a critical warning signal that alerts drivers to the potential danger of a train nearby. It is designed to ensure that drivers do not cross until it is truly safe to do so. Although a train may have passed, there might still be another train coming, and the flashing light remains active to prevent accidents.

The other options may seem plausible, but they do not adequately address the safety precautions necessary at railroad crossings. For example, the idea of crossing as soon as the train clears does not account for any additional trains that may be approaching. Similarly, a flashing green light is not a standard signal used at railroad crossings; thus, it does not indicate safety for crossing. Lastly, while verifying that no trains are approaching is a smart practice, the definitive rule is to wait until the flashing red light is no longer illuminated to ensure maximum safety on the tracks.