Lol seven pople voted lock this topic and let it die
And
EIGHT people voted Epic or good...
The first step and probably the closest thing we'll ever have to a rollercoaster is a vehicle which can be guided along a track 100% of the time. The box train is fine, but it comes off the rails occasionally.
Alternatively: A vehicle driven by ONE person (in say a box at the side) and the action of moving has a value of 0 for all velocities, and the animation moves the carts and the mountpoints, giving the idea that the player is in a rollercoaster.