When I toured in New Zealand, I got an AA membership to get a hold of maps that showed all the alternative routes to the main highways. Many of these were dirt and gravel roads however the alternative was, at least on the north island, crazy drivers. On the south island, the traffic was down to about a vehicle an hour. The only truly crazy drivers I encountered on the south island were a tour bus company that would not move over the center line regardless of the fact that the two of us were the only things on that stretch of hwy. The downside was the surface of the "metaled" or gravel roads was aggregate of a size we call "inch and a half binder". It wouldn't wash off the road like smaller rock would.
Interstates, in addition to wide, flat tire potential, trash filled, shoulders, have generally easier grades.However they also have grinding boredom and with that drivers who are not likely to be paying close attention to their driving. Not to mention they tend to isolate traveling from the territory you are traveling through. I also avoid them unless the alternative is worse.
Dirt roads are a possible alternative except for rain and wash boarding. Having a bike with a suspension frame or front fork might help. Speed is the downside of dirt but the upside is peace and quiet.