Nearly all states have traffic data available - most have it in convenient map form rather than tables.
Google "State name, DOT, traffic count" and you should get a good link.
The state-produced bicycle maps vary considerably - for good to poor.
Most offer three shades of roads for suitability with little specific data. (Arizona's is one such)
Many states also offer data for county roads, too.
For example -
Kansas - http://www.ksdot.org/burtransplan/maps/CountMaps/Districts/countmap2011.PDF
Southeast Kansas - http://www.ksdot.org/burtransplan/maps/CountMaps/Districts/d4rs10.PDF
Generally speaking, only busier roads will have paved shoulders.
One has to choose between a fairly busy road with shoulders or a quiet one without.
(Obviously, you want to avoid a busy highway without shoulders, eh?)
Another way to get magical empty roads is to finid routes with short unpaved stretches.
For example - between Archville and Beantown the main highway is 30 miles all paved -
But there is a back road that's 34 miles with 5 miles unpaved. It will usually have almost zero traffic.
ACA tends to route only on paved roads, also avoids rough bituminous surfaces as well.
But with the bumps comes the magic - even abandoned stretches of highway with cracks and grass growing.
I rode along the Mississippi bluffs one fall on an abandoned highway - perfect!