Human-powered roller coaster, welcome to the Dumb Ideas Club
This really takes the stupidity cake. Looking at the first few pictures, I thought the "Skycycle" in Okayama, Japan, was a sort of bike-ride-meets-skyway. You know, something that you could pedal around on at a nice, leisurely pace to get a birds' eye view of sights on the ground. But, no. It's a roller coaster. You get on it, and you pedal, and you go wheeeeeee.
This is scary for a number of reasons. Okay, so it might be eco-friendly because it's all done by manpower. But personally, I like my roller coasters to be automated. You never know what will happen when you put idiots in the driver's seat (and there are a lot of idiots out there). Plus, take a look at the seats on this thing. They don't look suitable for a golf cart, let alone a roller coaster.
Environmentally sustainable technology is awesome, but please, let's keep it safe. For a future "green roller coaster," how about some biofuels? Hmm?