My coaster is based on a Mobius Strip. The track has rails on top and bottom. The vehicles ride the upper rails then do a half-twist to an inverted position on the lower rails. Because of the twist, the upper and lower rails form one long track. The vehicles do 2 loops on the track, passing under the station on the first loop and stopping in the station at the end of the second.
I mocked up this ride on a Wild Mouse Coaster scale. The single car vehicles are mounted on a yolk with a vertical rotation. This keeps the riders upright when the vehicle flips to the inverted side of the track and gives it a little swing. Because of the geometry, this also means the vehicles travel backwards when inverted.
As always, there are tons of technical issues to work out with something like this (load and unload being a big one). Also, please forgive the jerky animation. I'm using the animation feature in Google Sketchup and there isn't a lot of fine control there. The flip-overs are especially wonky. I think the idea gets across though.
After I came up with this and figured out how to make it work, I did a little research. Turns out this Mobius Strip idea is not a first but I think my interpretation is unique. THIS is the most common Mobius interpretation. Just wanted to say I'm not stealing it. :-)
Enjoy the ride...