Symbolism, Imagery, Allegory
You know how everyone lusts after the guy with the Porsche because he looks like he's got it all made?
Well the characters in this book are no different. They dream about being wealthy… and that means they dream about cars.
But they don't all dream about Porsches, although Young Ju, who "dream[s] of an Oldsmobile and a Porsche sitting in a spacious garage lined with shelves and neatly hung tools" (18.31), clearly does.
Uhmma, for instance, really wants an Oldsmobile (which is probably why Young Ju wants one too). For Uhmma, the Oldsmobile is that classic American car that's "big enough to hold a whole family," nothing like a Toyota that, after an accident, is "bent and completely broken" (18.29).
Either way, none of these cars are realities for the Park family, who instead own a station wagon "whose right back door flies open when you take left turns too quick, gets honked at every time it inches up a hill, and leaks black oil all over the street" (18.30).
Cars: in this book, they show what class characters are in and how far they still have—and would still like—to go.