What is the primary purpose of the flashing red lights at a railroad crossing?

The primary purpose of the flashing red lights at a railroad crossing is to indicate that a train is approaching. When the lights begin to flash, it serves as a clear warning to drivers and pedestrians that they must stop and wait for the train to pass. This warning is critical for safety, as trains can travel at high speeds and may not be able to stop in time if someone attempts to cross while the lights are activated. The flashing lights are supplemented by gates or signals, depending on the crossing, to enhance safety further.

Regarding the other options, while slowing down approaching vehicles might be a consequence of the lights flashing, it is not the primary function. The warning of potential hazards is more generalized and would apply to various situations, but it is not specific to the action of a train's approach. Lastly, the signal of the crossing being safe contradicts the intent of the flashing lights, which is to indicate that it is not safe to cross the tracks at that moment.