In the children's literature I'm reading, transportation often serves its literal purpose: moving characters in the story from one place to another. Even when having transportation in the story lets the characters discuss other things, the trip has the same purpose it would in real life.
In other cases, however, transportation's role is clearly metaphorical. Author Jacob Abbott developed an extended metaphor with a steamboat in his 1832 work Young Christian. Abbott informs the young reader that according to the Bible, a person's time on each is merely a period of probation. He then proceeds to illustrate this with what he calls "familiar examples, drawn from the actual business of life" (307). Abbott selects the steamboat as a metaphor and notes that any steamboat must be "proved" before it can be put into service. He enumerates the things which could possibly go wrong with a ship—such as poor materials or poor construction—and notes that the engineer must carefully inspect every portion of the vast new machine in over to ensure that it is working properly. The engineer in this story takes days, even weeks, to insure that every joint, bearing, valve, and gauge is in proper working order. After the engineer is satisfied with the quality of the work, only then can people climb on board.
For Abbott, the steamboat embodies both power and restraint. he tells his young readers: "And though she has within her bosom a furnace glowing with furious fires, and a reservoir of death—the elements of most dreadful ruin and conflagration—of destruction the most complete, and agony the most unutterable; and though her strength is equal to the united energy of two thousand men, she restrains it all" (310). But the technology was not invoked to scare the reader. Rather, the steamboat served as a metaphor for the readers themselves. By the end of the story, the purpose of the metaphor is clear to the reader. Each of us, Abbott tells us, has within us "susceptibilities and powers, of which you have little present conception, energies, which are hereafter to operate in producing fulness of enjoyment or horrors of suffering, of which you now but little conceive" (311). Just as the engineer had to closely inspect the steamboat before launching it and taking lives into his care, so too should the reader inspect him or herself and change anything which needs fixing. Like a mechanic readying a steamship, American youth were to inspect hand modify their hearts. Abbott admonished his readers: "You are on trial—on probation now. You will enter upon active service in another world" (311). The steamboat—what must have been commonly known to his young readers by the 1830s—served as a lesson in how to prepare oneself for life after death.