You know who isn't like a rolling stone? A Zax. Both Zax, actually.
The highway in "The Zax" symbolizes the nature of the world. Deep, right? But hear us out. The highway allows the world to grow by connecting one place to another, new people to new areas. If you look closely, the line "Of course the world didn't stand still. The world grew" appears right before the highway is introduced (Zax.29).
This worldly road is also a nice foil for the Zax. Just look at the way it shapes itself around obstacles while the Zax very stubbornly refuse to move any way they don't want to move. The highway helps the world grow and get where it needs to go. Moral of the story: if you want to do the same, be like the highway—not like the Zax.