The
Silver Comet /
Chief Ladiga trails run 94 miles from suburban Atlanta, GA to Anniston, AL. They're rail trails, so they're pretty straight and flat. According to Wikipedia, combined they form the second-longest
paved trail in the country, after the Paul Bunyan Trail in MN.
Of course, Atlanta is currently working on connecting the Silver Comet up to other trails in the metro area (the Beltline, PATH400, Big Creek Greenway, Atlanta-Stone Mountain Trail, South River Trail, etc.) so in another 5-10 years (hopefully) you'd be able to ride from Anniston, AL to Conyers, GA, a distance of about 140 miles, almost all on dedicated bike trials. (The route would look something like
this.) In fact, if you wanted to do that route today, the only sketchy parts would be the segments along Atlanta Rd/Marietta Blvd and on Howell Mill Rd -- pretty much all the other on-street portions are reasonably decent to cycle on.