Nothing in my post excludes Canada. I thought it was a foregone conclusion that the Alaska Highway would take top honors now that a Wal-Mart has opened at Whitehorse. You may have noticed that I said "between Wal-Marts". the Alaska Highway has only one Wal-Mart that I know of at mile 887/1476km. I don't remember seeing that one in August of 2002 but I do remember a post by Charles Watts on that subject. http://www.fiberglassrv.com/board/read.php?TID=845
In the lower forty-eight, the 683 miles of US 50 between Grand Junction, Colorado and Fallon, Nevada would be a top contender.