What shall be done to stop an approaching train?

When it comes to signaling an approaching train to stop, swinging a light horizontally is the correct action. This method is a widely recognized signal among railway personnel, signifying an urgent need for the train to halt. The horizontal swing captures the train operator's attention effectively and communicates the critical message clearly.

In contrast, other signaling methods, such as swinging a light vertically or diagonally, may not convey the same urgency or clarity to train operators. Additionally, swinging a light in circles does not provide a definitive signal and may confuse rather than inform those on the train. Thus, employing a horizontal motion is the most effective way to communicate the need for an immediate stop when a train is approaching.