I have used the Surveyor 2.0 method of creating double tracked lines, and it is a big time saver. A couple of hints to do it without many problems:
Build a stretch of single track just as usual. But make sure all the spline point elevations are set to the desired fixed elevation and also perform the straighten track process as needed. You want the elevations and straightened sections to copy from the original to the clone. Also, it is best to not attach the new track to any existing track just yet. This is because you will double click to select the entire newly created track, but you don't want to go beyond the new track. Then it's just a matter of double click, control key held down, and drag with the fine adjustment tool to clone the track.
There will be some fine tuning because the track on the outside of a curve will need to be longer than the track on the inside of a curve. Just a matter of moving spline points a bit.