Eisenhower Interstate System naming rules:
All interstate highways start with the letter I and end in a number.
For north-south interstates, the numbers used are odd. For east-west interstates the numbers are even.
Numbers are assigned by region. For east-west interstates the southern routes use the lower numbers (ex. I-4) and the northern ones use higher numbers (ex. I-92).
For the north-south interstates the lower numbers are in the west and increase toward the east.
All transcontinental (coast-to-coast or border-to-border) interstate numbers end in 0 or 5 (ex. I-65 and I-90).