When are drivers required to wait at a railroad crossing?

Drivers are required to wait at a railroad crossing when there is a flashing red light because this signal indicates the imminent approach of a train. The flashing red lights serve as a warning to drivers that they must stop, ensuring safety for both the drivers and any potential passengers in the area. This regulation is in place to prevent accidents that could result from attempting to cross the tracks when a train is approaching, which may not be immediately visible to the driver.

While there are scenarios associated with the other choices, such as the need to be cautious when there are multiple tracks or following direction from a flagger, the flashing red light is the most definitive indication that a driver must come to a complete stop and wait until it is safe to proceed. Waiting for a train to pass is also crucial, but the flashing light represents an immediate and required action regardless of the circumstances surrounding recent train activity or track conditions.