Check out Michigan's Trail systems. They have about 2700 miles of trails; some of them meet your criteria. Also look at Idaho's Trail of the Coeur d' Alenes.

Rails to Trails

Australia's Rail Trails
https://www.railtrails.org.au/

In this thread, I posted the story of our trip on the longest (or possibly second longest now) rail trail in Victoria. See posts 34, 37 and 38.

2018 - Your Short Tours

Interstate is tough. But for long trails, there are some in MN.

Some specific ones are: The Katy Trail. The Mickelson Trail in SD, which is very scenic but not flat. The Olympian Trail in MT, which is less developed, not flat, but scenic. It connects with the Route of the Hiawatha Trail, which takes you into ID via St. Paul Pass. You can also transfer from the Olympian to the NorPac Trail that will take you across Lookout Pass into ID where you can connect with the Trail of the Couer d'Alene. The NorPac is also more rugged than your typical rail-trail and not flat, but also very pretty. It's technically open to vehicles since and is managed by the U.S.F.S. I saw one car when it rode the MT side. What little traffic there is moves very slowly. The Cd'A trail is paved. And let's not forget the GAP/C&O combination that will take you from Pittsburgh to D.C. In PA there is the D&L system, which has a few gaps in places.

The Silver Comet Trail

Suburban Atlanta, Georgia to Anniston, Alabama

Silver Comet Trail Photos


-Tim-

Quebec has a few trails, the most famous being the 200km Le P'tit Train du Nord. You could make 400-500mile tour with very little road riding, with a shuttle at one end and a train the other. The solid lines are bike paths, the double lines are on road: https://carto.routeverte.com/en

BC has the KVR (Kettle Valley Railway), several hundred Km's of rail trail. https://bcrailtrails.com/
You can also travel across most of BC on a semi off road system of trails as noted in this race https://www.bcepic1000.com/

A pic from the KVR

Google Maps bicycle option
google maps shows most every trail, from short ones in city parks to the longest ones.

Pull down the left side menu and select Bicycling.

You have to zoom in to at least the "10 mile" zoom level before the bike trails display.
Zoom way in on trail to see it's name repeated along the line, then you can google that trail name for more info.

For example, southern PA with the GAP trail heading SE from Pittsburgh.
https://www.google.com/maps/@40.2283.../data=!5m1!1e3

What are the solid or dotted lines?
The trail markings don't all have their previous meanings, and there's no info from google itself on the new markings.

previously,
solid green line: a paved trail
solid brown line: unpaved trail
dotted line: a bike lane on a road.

Now:
dashed green line: unpaved trail?
solid dark green line: might be paved or unpaved trail.. why! See the GAP trail around Ohiopyle, some of it is solid, some dashed, but it's all the same unpaved, crushed stone surface.
solid light green line: bike lane on a road
dotted line: bike friendly road. (some are more "friendly" than others, though.)
solid brown: unpaved trail or dirt path.
The current map legend. Doesn't show the dashed lines here.



Street View!
A few trails have Street View, from a bicycle towed camera.
zoom in, drag the yellow "street view guy" onto the map and see if the trail is included.
For example, the Little Miami Trail near Loveland OH:

There's a huge expanse of rail trails in central Iowa, all interconnected. You could easily spend three days in central Iowa riding dedicated trail.

Long trails not yet mentioned:

The Katy Trail
The GAP Trail, Great Allegheny Passage. There's more trails in the Pittsburgh area, too.
The C&O Canal Trail, connects to the GAP trail
The New River Trail, from Galax WV
The Erie Canal Trail, Rochester NY
The Little Miami Trail, Cincinnati to Xenia OH, with interconnects to many other trails. paved.
The Ohio & Erie Towpath trail, south of Cleveland, including Cuyahoga Valley National Park. And more trail south of Akron OH.


Scenic:
The Virginia Creeper Trail. AbingdonVA. 34 miles, extremely scenic, following a mountain creek valley, with whitewater and many bridge crossings. The round trip, 68 miles, is a full day ride, since there's a lot of elevation gain and many scenic stops along the way.

Since you appear to be in Omaha, NE, you should check your own back yard first. There the Cowboy Trail from Norfolk to Valentine (and you can realistically, but not officially, ride it to Crawford). There is also the Mo-Pac and Homestead Corridor to the southwest of you. There's also the Steamboat Trace running from Nebraska City south to just south of Brownsville.

Further afield, there's the Katy/Rock Island over in Missouri and the Michelson Trail in South Dakota. There's also the Flint Hills, Kanza and Landon Trail in Kansas.

And, although not "rail trails", there's a rather extensive network here in Colorado. You can ride trail from Denver to Loveland Pass and then ride trails from Keystone to almost Grand Junction going west. South of Denver, there are trails that stretch almost to Colorado Springs and trails north along the Poudre and Platte River. You can also ride trail from Denver to Boulder.

And that just scratches the surface.

Check out rails to trails .com.

Around you- Cowboy. Michelson. Katy.
or come to central Iowa and ride hundreds of miles of connected trail.

The Capital Trail in Virginia connects Richmond and Jamestown. 53 miles long.

I have been very interested in this trail, I seem to get mixed reports on trail surface. Maybe because it is a mixed lot.

I really wouldn't be interested in rough trail. Something similar to the Katy or GAP if you have ever ridden them. Maybe even slightly less quality then that would be OK. Any good sections that fit that bill?

The section around Myra Canyon is well maintained and most the rest is adequate. I haven't done those other trails you mention but this is dirt, rock, sand, ruts etc... but not singletrack or technical. I don't think I'd use a road bike perse as thin tires would wallow but a gravel bike or rigid mtb style tourer with 26x1.75 tires would do fine.

Yep, the only caveat to the OPs request being is that there are a lot of connectors between the randomly completed trails, it is hard to ride more than a few dozen miles without following some sort of open-to-motor-vehicle traffic.

That said, I still highly recommend them, and can't wait for the day the Airline Railway and the Iron Belle trail are fully complete.

I just wish Tasmania would get on board.