Rollercoasters are, by and large, designed to give you a vicarious thrill by simulating danger and peril on a seemingly out of control track. Of course, it's all controlled and calculated and safety checked and we know that it won't really kill us.
Unless, of course, you happen to take a ride on the Euthanasia Coaster designed by Royal College of Art PhD student Julijonas Urbonas. Its very function is to kill its riders -- as in make them dead by the time the cars return to the station.
This ghastly amusement ride manages this feat thanks to gravity and force. Amazingly, though, Urbonas claims that the coaster would dispatch its victims humanely. Thanks to the g-forces, the brain would be starved for oxygen and the rider would experience thrills, euphoria, tunnel vision, loss of consciousness, and then death.
Its unlikely that Urbonas' rollercoaster would ever be built, but I'm sure he's happy that we all slowly die waiting in the lines to ride the non-lethal ones.