Train operators must NOT advance the controller beyond which setting while operating from the leading car?

When operating from the leading car of a train, it is essential for train operators to adhere to specific safety protocols regarding the settings on the controller. The correct answer indicates that the train operator must not advance the controller beyond the series setting.

The series setting is typically used for low-speed operations or for starting the train effectively. Advancing the controller beyond this setting can result in increased power that may cause the train to lurch forward unexpectedly, leading to potential safety hazards, especially in low-speed environments, such as stations or junctions. This setting helps in controlling the train's traction and ensuring stability during operations.

By limiting the controller to the series setting, operators can ensure a safer start and maintain better control over the train's acceleration and braking. This adherence to the series setting prevents unwanted rapid acceleration or loss of control, which is crucial in avoiding accidents and ensuring the safety of both passengers and crew.