The Tennessean ran Washington, Lynchburg, Roanoke, briston, Johnson city, Morristown, Knoxville, Chattanooga, Huntsvville AL, sheffield AL, Memphis. It took right at 24 hours, and that was the premier fast train on the route. Add another 4 for New York to Wahington. At one time, say up to the early 1950's, if that late, there was on overnight sleeper on the Tennessee Central, Knoxville, Harriman, Crossville, Cookeville, Lebanon, Nashville. Leanon to nashville is now the route of teh only commuter line into Nashville. They spent $30 million on the track to get it up to 60 mph for most of the distance, a speed limit that had never been achieved in the past. by the way, that $30 milion prbably represented more work for the dollar than any other publically funded railroad upgrade within the last 50 years.
The railroad is gone between Harriman and Cookeville and betweeen Bruceton adn Memphis. Columbia - Jackson never was, and is not on any sort of reasonable route between Nashville and Jackson, whethere road or rail.
Here again, we are looking at a completely new line in order to achieve any meaningful speed, as much of the line is in Appalachia and is anything but straight.
While we are dreaming, let's rebuild Saluda grade straighter adn flatter. In a lot of ways, both freight and passenger this makes reasonable sense operationally and for passenger access to Asheville, but teh economics are not there, as it would be a very costly proposition to do.