Do It Yourself Rollercoaster

This came to me in a dream. It was a rollercoaster for cars. You could drive your car on this track, and signs told you how fast you had to go to do certain things, like the loop. Yes, you could actually drive through an upside-down loop if you had enough speed.

Now, obviously the technical challenges aren't nearly as much of a problem as the safety and legal liability issues. This is not an idea that will become reality (although it was REALLY fun). It does make me wonder about the possibility of a self-directed multiple-route rollercoaster ride, though. There might be a safe and fun way to make that work.