A wonderful image is used to describe his getting down from the train: Like a word dropped from a long sentence .The uniqueness of the image lies in the highly evocative visual picture of an old man dropping off from the train as though he is no longer relevant to the train which will now move forward with other people to their destinations.The old man is just a word in the syntax of life. The sentence that is long enough to carry several words forward each contributing to its overall meaning now drops off one stray word, which is no longer required.
The other interesting image is the eyes and vision, which occurs in the poem again and again. The suburbs slide past his unseeing eyes is a pretty image. The second one is his eyes dimmed by age fade homeward.
Above all we may look at the dexterous use of words to convey the “twilight” atmosphere in the poem : evening train, yellow light, unseeing eyes , his eyes dimmed by age fade homeward ,gray