What makes a successful roller coaster is the rail that hold it so when it might make a loopy loop, it will not fall over and squish all the people to the ground.
But before someone makes a roller coaster they always have to use a test dummy (a robot) so you can test the roller coaster out.
Here is what I found:
"A roller coaster is an amusement ride developed for amusement parks and modern theme parks. LaMarcus Adan Thompson obtained a patent regarding roller coasters on January 20, 1885, which were made out of wood, but this patent is considerably later than the "Russian mountains" described below. In essence a specialized railroad system, a roller coaster consists of a track that rises in designed patterns, sometimes with one or more inversions that briefly turn the rider upside down. The track does not necessarily have to be a complete circuit, as shuttle roller coasters demonstrate. Most roller coasters have multiple cars in which passengers sit and are restrained. Two or more cars hooked together are called a train. Some roller coasters, notably wild mouse roller coasters, run with single cars."
Hope this helped! :D :)
I included a picture so you can see the railing in how it is to not let the people fall when they are riding. :)
