(I'm thinking of starting a "did you know" category, and putting random tidbits in it like this. Anyone have any strong feelings about this? :contact: me and let me know!) How are interstate highways numbered in the United States? Believe it or not this is something the goventment does that makes sense. All east-west interstate highways are even-numbered and increase from south to north. So, east-west Interstate 80 is north of I-70. North-south interstates are odd-numbered and increase from west to east. City bypasses and spurs have triple digits and are numbered odd or even depending on their directional orientation. (And thanks to my friend Rich for providing this interesting tidbit).