Which signal indicates that a train is approaching?

The indication that a train is approaching primarily involves a combination of flashing lights and an audible alert, such as a bell or horn. This system is designed to ensure that pedestrians and vehicles are clearly warned of an oncoming train, as it provides both visual and auditory signals. The flashing lights attract attention and signal imminent danger, while the bell or horn serves to alert those who may not be looking directly at the crossing. This dual approach is crucial for safety, as it enhances the likelihood that individuals in the vicinity will be aware of the approaching train and take appropriate precautionary measures.

In contrast, while a single steady light could signify various conditions, it does not convey the urgency associated with a train's approach. Similarly, a flag waved by a worker is typically employed in specific operational contexts rather than as a standard warning for an approaching train. A loud whistle from the train might signal its presence, but it is not as universally recognized or effective as the established system of flashing lights and sound alerts at crossings. Thus, the combination of flashing lights and a bell or horn is the most effective and widely understood indication of a train approaching, highlighting the importance of clear communication in ensuring public safety near railway crossings.