How should a train approach a Subdivision "A" signal displaying Yellow over Red with an illuminated "S"?

When a train approaches a Subdivision "A" signal displaying Yellow over Red with an illuminated "S," the correct response is to approach at the allowable speed and then continue on the main route. The yellow indication typically means that the signal is cautioning the train to prepare for a stop at the next signal. The illuminated "S" signifies that the train should be prepared for a speed restriction ahead.

In this case, the train cannot proceed at its maximum speed but rather must observe the signal's instructions to ensure safety. This approach allows the train to maintain enough momentum while still being prepared to reduce speed if necessary. By approaching at the allowable speed, the train crew can react appropriately depending on what is ahead while also adhering to the regulations and safety protocols for train operation in that segment of track.