In which situation is flag protection not required for a train on the same track?

The correct answer indicates that flag protection is not required if the train is within Automatic Block Signaling (ABS) limits and there are two signals protecting the rear. In this context, ABS systems are designed to manage train movement along a track by utilizing signals to convey movement authority and track conditions. When a train is within these limits and is supported by signals that indicate it is safe, there is a built-in layer of safety that mitigates the need for additional flag protection.

Two signals protecting the rear serve as a clear confirmation that the area behind the train is also secure for operations. This system is structured to allow trains to operate more efficiently while still adhering to safety protocols. It implies that there is adequate protection provided by the ABS signals, which are specifically designed to prevent collisions and accidents on the track.

In situations outside of ABS limits, in maintenance zones, or where signals do not indicate a clear or safe condition, flag protection would typically be necessary to ensure safe operations.