What does it mean if the red lights at a marked railroad crossing are flashing?

When the red lights at a marked railroad crossing are flashing, it indicates that a train is approaching the crossing. This is a safety feature designed to alert drivers and pedestrians that they need to stop and not proceed through the crossing until the lights stop flashing. The flashing lights serve as a critical warning signal, allowing people time to react and avoid a potentially dangerous collision with a train.

Other options suggest different scenarios that do not align with the function of the flashing red lights. For example, indicating that it is safe to cross would contradict the warning provided by the flashing lights, and stating there is no train activity also goes against the signal's purpose. Lastly, the notion that the crossing is closed does not accurately reflect the immediate need for caution prompted by the lights' activation.