Buck used the "major cross country" Interstates, which end in the number 0 or 5. On the Interstate Numbering system, even numbered routes go east to west, with small numbers in the south and larger numbers in the north. Odd numbered routes run north and south, with smaller numbers starting in the west. For example, I-5 runs from Washington to California, while I-10 runs from Southern California to Florida. Interstates ending in 5 or 0, like the ones buck used, theoretically run from border to border or from coast to coast - although most of them actually fall a little short of those goals.