What must not be exceeded according to track warrant, track bulletin, or radio speed restriction?

The correct answer is that the specified speed until the rear of the train clears the restricted area must not be exceeded. This means that operators must adhere to the speed outlined in the track warrant, track bulletin, or any radio speed restrictions to ensure safety and compliance within the designated area.

This rule is critical as it helps prevent accidents and ensures that trains operate safely in areas where there may be work crews, maintenance activities, or other types of restrictions in place. Ensuring that the speed does not exceed the maximum specified until the entire train has cleared the restriction maintains safe operational conditions for both the train and any personnel working in proximity to the tracks.

The other options provide different contexts that are not applicable as the primary focus in this context is on the specific speed restrictions in operational scenarios. The train crew's set speed, the maximum allowed by federal regulations, and the overall authorized train speed are all essential for operations, but they do not account for the specific situation being addressed here, which deals with constrained areas requiring careful attention to the speed of the moving train until it fully exits that area.