I'm not even familiar with 60! Maybe I drove part of it when I was in Arizona last year
That would have been US60, not an interstate. Arizona has I10 and I40 running east/west.
I know the original US highway system (laid out in the ‘20s) starts in the east and increases going west. So I95 roughly follows US1. (I95 actually starts at US1 in Miami.)
I don’t know much about the east/west highways, but I wouldn’t be surprised if there was a similar pattern.
nacl