What does a crossbuck sign with a flashing red light indicate at a roadway?

• It signifies a pedestrian crossing zone and advises drivers to slow down and yield to pedestrians.
• It indicates the presence of a nearby train station where passengers can board or alight trains.
• It indicates that the railroad crossing is under construction; drivers must not proceed.
• It signals drivers and pedestrians about an upcoming railway crossing and advises them to be prepared to stop for approaching trains.
  Explanation:

  "At many crossings, the crossbuck sign has flashing red lights and bells. When the lights begin to flash, stop immediately! A train is approaching."