Here's a first go. Built a two oval racetrack, then changed it with 087 snake, 072, 057 curves on lower level, 072, 057, 042 on upper level 10" elevated with tunnel at one end, bridge over snake.
Keeps those biggies from wigglin' around on 'lil turns.
Concept ok?
Go flat?
Switches and other features will be on top level.