It probably was inevitable that someone would try to tie aerial flight and a rollercoaster together; Kittyhawk was only eight years in the past.
The invention further contemplates a pond or body of water for the car to alight upon when descending, thereby avoiding all shock and adding further to the variety and amusement of the pleasure seeker.You don't have to build a working prototype to secure a patent. If Mr. Aitken had, he might have found the challenge of devising a railway car capable of transporting three people down a steep slope, into the air, and to "alight upon" a body of water an insurmountable one.
Any type of wing device designed to create lift would have also done so on the initial downhill, destabilizing the craft.
Seat belts were not mentioned.
So you've either got a prematurely-flying deathtrap bathtub smashing down the side of the structure, or a successful launch into the air in a rickety wing-laden bathtub slamming into the lake from what appears to be about 30 feet in the air, assuming you're still in the damned thing when it lands. So many possible scenarios.