What should a train operator do if they observe a white light being moved rapidly up and down?

The presence of a white light being moved rapidly up and down is an important signal that typically indicates an emergency situation or a warning from personnel on or near the tracks. The appropriate response for a train operator in this case is to blow two short blasts of the whistle. This action serves to acknowledge the warning being conveyed and to alert any nearby personnel of the train's presence as a precaution.

In this scenario, blowing two short blasts is a standard communication protocol that demonstrates awareness of the signal and helps to ensure safety. It is essential for train operators to respond to such signals appropriately to prevent accidents and maintain safe operations.

Other options, such as stopping the train immediately or increasing speed, would be inappropriate responses to this specific signal. Stopping immediately could potentially cause unexpected issues, while increasing speed would clearly be dangerous and irresponsible in the face of a warning signal.