State Roads in the US state of Indiana are numbered rationally: in general, odd one-digit and two-digit highways are north–south highways, numbers increasing toward the west; even one-digit and two-digit highways are east-west highways, numbers increasing toward the south, the opposite of the Interstate Highway System. Three-digit routes are related, as a rule, to the single-digit or two-digit parent US or State Road; thus State Road 205 (SR 205) is related to SR 5 and SR 120 is related to U.S. Highway 20 (US 20).