High Quality Content by WIKIPEDIA articles! This list includes the primary (one- and two- digit) Interstate Highways of the United States, with cross-references to their associated auxiliary (3-digit) routes. Even route numbers are assigned to east–west routes, generally from south (e.g., I-4) to north (I-96), with coast-to-coast and other long-distance routes ending in `0`. Similarly, odd route numbers are assigned to north–south routes, from west (I-5) to east (I-99), with border-to-border and other long distance routes ending in `5`.