Couple of things - -
Low-traffic roads usually do not imply a great deal of accommodations.
The really sweet low-traffic roads have considerable distances between services.
Also - -
What time of year makes a huge difference.
And whether or not you are willing to do dirt/gravel or bike trails.
Right off the bat -
Coastal Washington, eastern Oregon, Sawtooth Mtns of Idaho, to Jackson, Wyoming.
Lots of sweet empty roads - sufficient services.
