I have had good luck using Google along with state gazetters. I just returned form a 448 mile tour around parts of TN and this was invaluable. I encountered 4 roads that where closed that I had to work around to reach my destination. This could be a problem on multi state routes as you have to have one for each state. I have been know to tear out the pages I would need and just take them.
This is not a perfect plan. I did end up on two roads, for a short time, that where a nightmare to ride on. I use to street view and satalite views from Google to help me plan on roads to use.
I also like to do research on places to stop, see, and bike shops for repairs should this become nessary.