 The original highway numbering system for North Carolina was established in the 1920s.Major routes were multiples of 10, with 10, 20, and 90 running east/west, 30, 40, 50, 70, and 80 running north/south, and 60 running as a diagonal route.These cross-state routes were used as a basis for numbering the two-digit roads that served as the major city-city connectors.