I'm from Montana, and I live in New Mexico, so I thought I knew something about empty. Far West Texas still had a lesson or two for me though. My wife and I drove over to Carlsbad on business but stayed to see the caverns again, and then decided to drive down 285 to Big Bend, which we had never seen. It's a bit like rolling yourself down some hundred mile long bowling lanes - start out pointing the right way and you can go a lo-on-ng way before you need to correct your steering.
There are big stretches in Montana with no people, of course, but most areas have some relief - mountains, hills, forests, lakes and rivers. That part of Texas - not so much. That all changes as you approach Big Bend though, with real mountains, limestone arroyos that are really canyons, and a real canyon for the Rio Grande. In my town, the big river has been thoroughly domesticated by dams and is often reduced to a muddy trickle, but while we were there, it was a real river, small but swift through the Big Bend.
It was probably the least populated National Park that I've been in - we drove for hours on the main roads hardly seeing another car. A nice but isolated place.