You might ask why someone would want to turn a perfectly good Toyota Prius into a roller coaster that moves at a mere 15mph. I ask why not?
When the Prius begins to brake on the upturn at the end of the track, it stores the kinetic energy generated as electricity, which is able to power all the lights in the room. Pointless? Obviously. But c'mon, it's fun. Expensive fun. [NotCot]