Möbius coaster
From ThorxWiki
The world already has the Möbius Loop roller coaster, however the name is a bit of a misnomer. It is realyl just one track which runs parallel to itself and loops the circuit twice to return to the same start position.
bah.
I want to see a true Möbius strip coaster. ie, where the track is suspended by the sides, and the actual rails run both above and below, meaning you complete the same loop twice - once inverted compared to the other.
Track design may be complicated to ensure G-forces at all points are safe and sane for riders? So some heavy lifting math would likely be needed to design this.