According to this article https://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_(one-_and_two-digit)_Interstates https://en.wikipedia.org/wiki/Interst

According to this article https://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_(one-_and_two-digit)_Interstates https://en.wikipedia.org/wiki/Interstate_Highway_System#Prim... there is no encoding in separate digits, only the whole number being odd or even has meaning. E.g I-10, I-14, I-30, I-70, I-72 etc are east-west and I-25, I-45,I-65, I-83 etc are north-south.