Symbolism, Imagery, Allegory
Throughout Feathers, characters constantly refer to how they live on "this" side of the highway, and how there's an "other" side of the highway where they never go. It is clear that the town in which Frannie lives is split into clear boundaries.
The highway is the geographic representation of the split that already lives inside people's minds. The residents of the town believe that there is a clear-cut place where someone "belongs" based on their skin color. That's why when Jesus Boy comes to their school a lot of the other kids push back, saying that he belongs on the "other" side of the highway:
She made a face, wiping her hand against her shirt like the smell was still on it. "Anyway, it's strange—you don't see white boys at this school. Much as I hate to say it, Trevor's right—the boy belongs across the highway with the other white people." (2.29)
People aren't legally bound to stay on one side of the highway versus the other—the geographic divide just happens to mirror the social and race-based divide that people already believe in. By crossing the highway and living in the black side of town, Jesus Boy and his family are challenging the idea that people belong in a certain place with no exceptions.