US Interstate Highways

Authorized by the Federal-Aid Highway Act of 1956 under President Eisenhower, the system was inspired in part by the 1919 Army convoy that took 62 days to cross the country, and by the German autobahn network Eisenhower saw during World War II.

Even-numbered routes run east–west (I-10 south, I-90 north); odd-numbered routes run north–south (I-5 west, I-95 east). Three-digit interstates are spurs (odd first digit) or loops (even first digit) of their parent route.