Hm, maybe every tick (have a set duration between each tick like 1/3 or 1/2 of a second) set the cart’s general left/right to the current rail piece/section’s orientation.
I don 't think it is possible to make a high-performing rollercoaster/cart system by using only the roblox physics engine — using CFrames seems by far the most effective solution.
The easiest ‘‘non-script’’ solution to your problem would, I believe, simply not make the cart exceed 300+ studs per second.
I wish you the best of lucks with your project, in hopes that my answer was able to help you at least a bit. Feel free to reach out if you have any other questions.
Yeah, I think this person should probably work with CFrame correctiob, client movement, get constraints to work, or your solution. I don’t see any other ways because past CFrame it might start to become “hacky” (if that’s a good word).