Thank you again for all your input.
I've got a lot to play with over the next couple of months. I do enjoy planning out routes, just wish Google Maps could be relied on when it comes to minor roads, so many times I have ended up on farmers properties here in Australia.

A suggestion at least until you get past Chicago is to use the mode of "auto avoid highways". The reason is there are some more remote unpaved roads you can find yourself on in New Mexico. Going up the Rio Grande River there is likely one spot (between Belen and and Socorro) where the most straightforward route is on side of I-25. The signage in New Mexico can be confusing telling you both that you are prohibited and to use the shoulder. In more populated regions other techniques may work better.

I cycled ~19000 km around Australia in 2001 - https://mvermeulen.org/oneyear/australia.htm before Google Maps was launched and so mostly use combination of local maps and most of my time was spent in sparsely populated regions and on sealed roads. The lower 48 US states have 10x the population in the same area as Australia but there will still be some sparsely populated regions along the way.
https://cimg9.ibsrv.net/gimg/bikefor...ff91b1f9d5.jpg

When I am in doubt on google maps, I switch to satellite view instead of map view. (But that does require a fast internet connection to speed things up.) If I can see a road on an air photo, that tells me if there is shoulder or not, or if the road even exists. This works poorly in heavy forest, for obvious reasons. But where there is a clear view of the sky when you are on the road, the reverse is true too.

And sometimes if you see a lot of vehicles in that air photo, that is a busy road.

A few weeks ago I was mapping out a route between a couple bike trails where I will need to go by road for several days. Did that by Google Maps, mostly with satellite view. I tried to find roads with almost no cars visible in the air photo maps, and if there were some cars, I looked for shoulder width.

Google maps has errors for sure. My condo association property is posted as No Trespassing because we are near a large school and have had a lot of vandalism on our property, small scale theft problems, excessive litter, etc. Google Maps has plotted two bike paths through our property, disregarding the no trespassing signs.

That however does not help if there is road construction because of the age of the air photo or if a bridge is closed. A closed bridge on an air photo might look open. And of course, when you plotted the route you may not know that there would be a closure in the next few months.

On the route I was plotting a few weeks ago, I also used satellite view to see air photos to double check some of the campgrounds I saw on Open Steet Maps. Some of those marked RV parks on the Open Street Maps, when I located those on Google maps I found they did not exist, or maybe existed and had a website, one was listed as permanently closed, some had tent sites, but some were mobile home parks with permanent residences only. And many were day camps for kids, not campgrounds at all.

One thought came to mind. If you are going from South USA, heading Northeast, Natchez Trace might be a nice piece of your route. It is a 440 mile highway that is operated by the National Park Service in USA. No commercial traffic allowed. Virtually no shoulder, but bicycles are allowed to ride in the traffic lane.

I did a bike tour on most of the Trace a year ago. I put a brief summary here:
https://www.bikeforums.net/touring/1...p-summary.html

That said, the downside of that route is that once you get to Nashville and that route ends, you are in hilly terrain and may have difficulty finding a good route north and east of there. There is no Amtrak route from Nashville. The map in my write up is the route we actually took, we did not do the first 100 miles of it, which starts at a community on the Mississippi River.

Natchez Trace to Duck River, Tennessee. ACA Great Rivers South to Cave-in-Rock. Underground Railroad (or maybe Ohio to Erie), Northern Tier, Bob's your uncle. YMMV

Might enjoy playing with:

https://cycle.travel/