What must be established on the adjacent controlled track before performing work ahead of the trailing end of the train?

Establishing on-track safety through a train approach warning is crucial before performing work ahead of the trailing end of the train because it ensures that personnel are alerted to the possibility of an approaching train. This warning system serves to communicate real-time information to workers, allowing them to take necessary precautions and maintain a safe working environment. It is a vital part of on-track safety because it minimizes the risk of injury from train movements by providing time for workers to clear the area or enact safety protocols.

While having standard operating procedures, communication with the train operator, and checking for train schedules are all important components of a comprehensive safety plan, they do not specifically address the immediate need for a warning system that deals directly with train approach, which is essential for ensuring the safety of workers in the vicinity of moving trains.