Which signal aspect indicates the train may proceed at a maximum speed?

The signal aspect that indicates a train may proceed at a maximum speed is represented by Absolute Medium Clear. This aspect specifically allows for the maximum speed to be attained under favorable conditions, signifying that all is clear ahead for the train to proceed at that speed.

The term "Absolute Slow Clear" is typically associated with a reduced speed, allowing trains to proceed but at a cautionary pace due to potential hazards or limitations down the line. "Flashing Slow Approach" signals a caution, requiring trains to slow down further as they near the signal or potential obstacle. Hence, while Absolute Medium Clear clearly indicates the ability to proceed at maximum speed, Absolute Slow Clear does not.

The inclusion of both Absolute Slow Clear and Absolute Medium Clear in the context of a signal that permits maximum speed would thus be misleading, as not all permit the same conditions for speed. Therefore, the correct identification of the signal aspect that allows maximum speed is solely represented by Absolute Medium Clear.