The southeast US is not as dense as the northeast, but TN, NC, SC, GA, AL, and FL have 55 million or so people in them, the majority living in or near major metro areas. Connecting those major metros using the existing interstate corridors as the general path, you'd get most of the remaining population within a short distance of this intercity railway. If the metros themselves invested in better intrametro (I'd say intracity, but it would be a misnomer) transit systems that connected to the intercity system it could be effective for the region.
