I have biked to and from NC on four different cross-country trips including my very first one back in 1987.
I am one of those who plans and then expects to toss some of the plans aside. But it is easier to do it that way than to encounter a closed road over a mountain pass that requires a 100-mile detour and wish you had known it beforehand.
You offer few details about your plans - time of year, length of time allotted, type of bike, camping or motels, your touring style - all of which influence route choice. If you are credit card touring with motels each night, then you may not be able to opt for the more remote roads. If you are camping and you are touring early or late in the season, then you need to use care in route selection to avoid inclement weather as much as possible.
Although I have been on much of the TransAm over the years and many tours, I have never followed any designated route. I like to strike out on my own. The advantages of the Adventure Cycling routes are that you are more likely to meet up with other riders and that there are more bicycle-oriented services.
In general, northern states are more bicycle friendly - with hiker/biker campsites, rail trails, bike stores in small towns, etc. Southern culture still places a premium on the automobile - the adult rider is seen as some odd fellow, at best. I may take flak for this - but with 100,000 miles of touring - there is a difference. Not to mention - - - dogs.
One thing in planning your own route is to consider funnel points - crossings of major rivers and mountain passes are two important considerations. Also, in the West interstate highways were often built on top of the old highway - so there isn't a side road. Riding on the interstate shoulder is legal in most western states and you may have to for short stretches - but it kinda defeats the purpose in my book.
Rivers -
The day of the ferry crossing is now almost a memory - although there remain a few ferries. Older bridges over major rivers are death traps - narrow with heavy traffic. Newer bridges have shoulders or sidewalks, but traffic leading to and from the bridges is often extremely heavy. Ferries let you enjoy the river first-hand while keeping car traffic to a minimum.
Mountain Passes -
The combination of terrain and wilderness areas (where bikes are prohibited) means that road choices in the West can be limited. In Wyoming, you basically have 5 paved choices on a 200-miles north-south line - - Hwy 296 thru Dead Indian Pass, US 16 thru Sylvan Pass, US 26 thru Togwotee Pass, Hwy 28 thru South Pass, and I-80 thru the Great Divide. Since I-80 is insane and Hwy 28 generally doesn't head anywhere that most cyclists are going - that leaves only three.
There are two important factors in any route consideration - traffic count (usually known as AADT - average annual daily traffic) and shoulder width. Obviously, if there is almost no traffic you don't need shoulders. If there is lots of traffic, you have to have shoulders to ride safely. Most states provide AADT info on their DOT websites. Most states do not provide shoulder width data - but there is Google Streetview - albeit cumbersome. Many states have a bicycle/pedestrian coordinator - and there may be a bicycle map. These vary in usefulness from Oregon's which is superb (but not available online) to Arizona's which is just a few pretty colored lines on the page.
For me - I use a rough AADT measure -
500 or less - divine
500-1000 - excellent
1000-2000 - O.K.
2000-4000 - tricky without shoulder
4000-8000 - shoulder essential
Over 8000 - exhaust hell even with a shoulder
The difference between county roads and state/U.S. highways is the manner in which they interact with the landscape. County roads tend to have lower speed limits because they lay on the land - not cut through it. They curve around ponds, go over hills, wind along streams. Yes, it means more pedaling - but, for me, the quality is where it is at.
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I'll toss out an idea at you since I know NC well from my early cycling days in the 1980s.
What about riding from the Outer Banks to the San Juan Islands of Washington? You can start your trip with a ferry ride from the Outer Banks/Ocracoke and end it with a ferry ride out to the San Juans.
http://www.crazyguyonabike.com/doc/p...=2A&size=large
http://www.crazyguyonabike.com/doc/p...=AC&size=large
There is some really nice riding in southern Virginia that misses the built-up areas of the NC Piedmont, then you can basically follow the NC/VA and KY/TN borders to Mammoth Cave hooking up with the TransAm crossing of the Ohio River at Cave in Rock - - an excellent river crossing.
http://www.crazyguyonabike.com/doc/p...=4z&size=large
The TransAm route across southern Missouri is one goat hill after another - just ask anyone who has done it. I might suggest the Katy Trail along the Missouri River west of St. Louis - and a crossing of the Mississippi on the restored historic Eads Bridge with a full view of the city and the Gateway Arch. (The Eads Bridge is built on top of stone arches so you have a 360 panorama.)
http://files.myopera.com/musickna/al...s%20bridge.JPG
Personally - I prefer crossing Nebraska to Kansas. Nebraska's terrain outside of the very flat Platte is one of rolling sandhills. Kansas can be flatter than a pancake on a sizzling summer grill. So if you took something like the Lewis & Clark from St. Louis to Plattsmouth, you could light out across Nebraska for the Black Hills (a cool reprieve from the Great Plains) and then Wyoming.
The TransAm has a big zig in the West from Pueblo to Yellowstone. If you are going to do a zig, I would suggest from Yellowstone to Glacier so your can take in some of the finest scenery to be found and ride Going to the Sun Road. Then you can continue on the Northern Tier out to the San Juans.
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If you are riding east to west, I would suggest a start date no later than early June. (Unless, of course, you are going to do century days every day.) That way you beat the worst of the heat in the East and may get through the Plains without too many scorching days. Also, by late summer the high country in the West is snow free - although you will miss most of the wildflowers and may have forest fire season to consider. (I had to detour around the Yellowstone fires in 1988.)
Anyhoo - feel free to e-mail me directly if you have any questions - - J
PS - Do you know how many Chapel Hillians it takes to change a light bulb?
Thirty-one. One to change the bulb - -
And the other thirty to talk about how nice the old one used to be.