I did the transamerica bike route (https://www.adventurecycling.org/routes-and-maps/adventure-cycling-route-network/transamerica-trail/ https://www.adventurecyc

I did the transamerica bike route (https://www.adventurecycling.org/routes-and-maps/adventure-cycling-route-network/transamerica-trail/ https://www.adventurecycling.org/routes-and-maps/adventure-c...) a few years ago. That route is mostly on roads with some trail sections. It makes for an interesting tradeoff: if you optimize for low traffic roads without worrying too much about about strictly staying on trails you can stay away from cars fairly successfully. In comparison, if you optimize for staying on trails as much as possible you may end up riding on busy roads connecting the trail segments. There's no right answers, life's built on tradeoffs, etc.