It depends on what part of the country your in, terrain, activity levels within that particular area, if it's a BLM crossing or cut-through road to a destination or not, etc. etc. Conditions can change dramatically year to year.
If you're main area of interest is staying within designated dispersed camping areas then those will generally be the better of the lot and maps are available from the local BLM offices. It's good to stop in for updated maps every year.
If you want more off the beaten track... Generally what you'll find is somewhat of a network of fairly decent roads with "spur" roads off of those that will greatly vary in travelability. Of course... some of those "decent roads" may be gated, or if there is no state sponsored activity in the area that year you may find it in disrepair or... in forested areas... covered in blow downs (With permission, they are generally more than happy for anyone willing to clear them). One thing to also be aware of. Many "back roads" are dead ends (or terminate in a "landing").
You have to be prepared to do your own scouting. Be it on foot, vehicle, or by air (where permitted).
To answer your question... Couldn't say!