Here in my part of Ohio everyone I know just refers the freeways as either
"I-##" or "##" if its a State Route, we say "SR-##" or again "##" which I guess you would have to know the nearby freeways to know which is a State Route and which is the Interstate.
"I-##" or "##" if its a State Route, we say "SR-##" or again "##" which I guess you would have to know the nearby freeways to know which is a State Route and which is the Interstate.