In the Walmart by me, the self-checkout is the usual fare (a large square area with about 10 stations), but right next to that are the regular aisles with conveyors, and two (three?) of them are self-checkout, but most people don't notice them because they look like any other cashier aisle, and are kinda' separated a bit with a candy rack between them and the square (boxed) area.
So while there is a line for the box, there's usually at least one of those tucked-away SC aisles open. Best kept open-air secret at the store.