A:  I would guess that the majority of engineers working with roller coasters have mechanical degrees. Most of us here have EE degrees, or Computer Science/Software degrees because we do the "control system" part of the coaster design. Specifically, we design the systems that keep the trains from getting dangerously close on multi-train systems. We also do the operator controls, track switch operations, and other "control system" functions. Some companies offer structural/civil engineering services for coaster designs, with regard to the foundations and other infrastructure items. But, for the classic potential energy = kinetic energy fun part of the coaster design, its the ME's that are in the middle of the action. There are only a few coaster companies, and I expect getting started with one would be a challenge because lots of other people think it is fun. Consider a job with one of the Disney engineering organizations like Walt Disney Imagineering. That is were I started years ago. Good Luck.