South Carolina seems to have adopted this practice as well. They will paint a black rectangle on top of the interchange bridge, and white numbers on the rectangle. So if the freeway bridges over the intersecting road, the number will be on one of the freeway bridges. Or if the intersecting road bridges over the freeway, the number is on the intersecting road's bridge. Basically it's whichever road is on top, so that implies that the numbers are meant to be seen from the air.