In Indiana, Mopeds are treated as bicycles. Except on bike trails, where motors of any kind are prohibited. So any road you could ride your bike on, mopeds are okay. Interstates are illegal in every state i'm pretty sure, and who would want to anyway?
Google maps has a option now that shows how to get from Point A to Point B without taking any highways. I've used that for journeys into unknown territory and it works pretty well.