What does a red light indicate on the M-7 exterior Door Lights?

A red light on the M-7 exterior Door Lights indicates that the door is open. This is a critical safety feature that ensures both the crew and passengers are aware of the door status. When the door is open, the red light signals that it is not safe for the train to depart, as passengers may still be boarding or alighting from the train.

The visibility of the red light serves as an important warning to platform personnel and train operators, making it clear that the train is not fully secure for movement. This mechanism helps prevent accidents and enhances overall operational safety. Understanding this function of the red light is essential for anyone involved in train operations, ensuring safety protocols are adhered to.