How does the extended metaphor in "The Railway Train" function in the
poem?

The basic metaphor for this poem is the comparison of a train to a horse “I like to see it laugh miles and let the valleys up” The interesting thing in this poem is that the word train in the word horse or never mentioned to the reader has to read the poem thoroughly this is a metaphor in which both the literal and figurative are not mentioned

hope this helped lolz