You could probably travel in either, but the difference is construction time. Drilling the tunnels and setting up supports takes much longer than building an above ground tube, so it's unlikely to see many tunnels outside of large population areas.
You could probably travel in either, but the difference is construction time. Drilling the tunnels and setting up supports takes much longer than building an above ground tube, so it's unlikely to see many tunnels outside of large population areas.
RE: Austin to Dallas