Final answer:
The implied main idea of the passage is that despite rushing, Justin had missed his train, as inferred from the description of his actions and his reaction upon arriving at the platform.
Step-by-step explanation:
The implied main idea of the passage where Justin is described racing to catch his train is that despite rushing, Justin had missed his train. This idea is evident not just from his hurried actions and the observation of train officials, but from the climactic moment when Justin witnesses the train leaving without him. This idea is implied rather than stated outright and requires the reader to infer Justin's situation from the presented details.