What does a yellow over green signal represent?

A yellow over green signal indicates that the train should proceed on the main route, but with caution. This signal means that the next signal is expected to be red, signaling a stop requirement. Therefore, it's essential for the train operator to be aware of this upcoming change in signal state and to be prepared to stop if necessary. The caution indicates that while the train can continue its journey, the operator should remain alert and ready for any potential changes ahead, ensuring safety and compliance with signal indications.