It’s quite rare to see a fully functioning roller coaster, especially one this large and complex and using 100% off-the-shelf LEGO elements. It does a look a little fragile at times, with the whole structure wobbling away in the high speed turns, but I’m pretty sure builder Hoezer2 has got it all figured out and it’s gonna hold up. The construction not only has the look and feel of a real roller coaster, but the turns and runs actually have a top speed of 10.3 kmh (6.4 mph) thanks to the use of Mindstorms EV3 motors and sensors.
I still can’t quite grasp how those carriages stay fixed to the tracks, which has always been my number one fear of roller coasters. But in the world of LEGO, minifigures don’t feel pain so it’s all good if they have to endure the occasional derailment.
The wheels on a rollercoaster do not ride on top of the rails like a train does, or they _would_ fly off the track almost instantly. If you look closely at the way the rails are constructed, the primary contact surface is actually on the inside of the rail. The wheels would then be oriented such that they have flanges on both top and bottom, which lock them onto the rails. Of course, a LEGO coaster weighs so little that you might be able to get away with that, but a real coaster will need to have load-bearing wheels that are oriented like those on a train, and secondary guide wheels that are oriented to hold the cars down against the track.