Interstate numbering works like this: Odd-numbered interstates north-to-south, with the numbers increasing from west to east. (That's why I-5 is on the West Coast and I-95 is on the East Coast.) Even-numbered interstates east-to-west, with the numbers increasing from south to north. (That's why I-10 runs along the Gulf of Mexico and I-80 runs across the upper tier of the country.)
Jan 10 2006, 5:37 PM
As a rule, like-numbered interstates don't cross each other (ie, an odd-numbered freeway won't cross another odd-numbered freeway). One notable exception, though, is I-85, which not only crosses I-77 north of downtown Charlotte, but also multiplexes (or runs concurrently with) I-75 through downtown Atlanta AND terminates at I-65 (at Montgomery) and I-95 (at Petersburg).