Final answer:
A train operator should slow down and proceed with caution when seeing an individual wave a green lantern up and down.
Step-by-step explanation:
When a train operator sees an individual step out of the way of the train and wave a green lantern up and down, the train operator should slow down the train and proceed with caution. The green lantern typically signals that the track ahead is clear but that caution should be exercised, possibly due to workers on or near the tracks, or other conditions that require careful operation of the train.
The operator should be aware of the situation, reduce speed, and be prepared to stop if necessary, but does not need to immediately stop the train unless further signals or circumstances indicate the need for it.