It took me a little bit to discover how easy straight track is to make (It takes very little time at all), so I understand that others are still confused as to how to make a piece of track remain straight while editing surrounding vertices.
All you have to do is select the vertices surrounding where you want your straight track and check the "strict" box. This locks the track into a straight position, and will not be affected by surrounding track (other than where the track is actually located).