In double colour light territory, what does green over flashing yellow signify?

In double colour light territory, a signal displaying green over flashing yellow indicates that a train is to proceed with caution while preparing for a possible change in the signal ahead. This signals to the driver that they can continue at a medium speed but should be prepared to respond to a more restrictive signal that may come up shortly.

The flashing yellow specifically indicates that the next signal could show a cautionary aspect, which requires the driver to maintain a level of vigilance and be ready to act as necessary, such as reducing speed if the situation demands. The combination of green over flashing yellow thus provides a clear instruction for ongoing movement while alerting the operator to upcoming changes in the signalling.

Understanding this signalling configuration is crucial for maintaining safety within railway operations, as it ensures that trains are monitored effectively and can react appropriately to upcoming signals.